DS004-2.2 APR 03

CYGNAL Integrated Products, Inc.

Page 1

PRELIMINARY

Mixed-Signal ISP FLASH MCU Family

C8051F300/1/2/3

C8051F304/5

ANALOG PERIPHERALS
-

8-Bit ADC

Up to 500 ksps

Up to 8 External Inputs

Programmable Amplifier Gains of 4, 2, 1, & 0.5

VREF from External Pin or VDD

Built-in Temperature Sensor

External Conversion Start Input

Comparator

Programmable Hysteresis and Response Time

Configurable as Interrupt or Reset Source

Low Current (

< 0.5µA)

ON-CHIP DEBUG
-

On-Chip Debug Circuitry Facilitates Full Speed,
Non-Intrusive In-System Debug (No Emulator
Required!)

Provides Breakpoints, Single Stepping, Inspect/Modify
Memory and Registers

Superior Performance to Emulation Systems Using
ICE-Chips, Target Pods, and Sockets

Complete Development Kit: $99

SUPPLY VOLTAGE 2.7V TO 3.6V
-

Typical Operating Current: 5mA @ 25 MHz;

11µA @ 32 kHz

Typical Stop Mode Current: 0.1 µA

Temperature Range: -40°C to +85°C

HIGH SPEED 8051 µC Core
-

Pipe-lined Instruction Architecture; Executes 70% of
Instructions in 1 or 2 System Clocks

Up to 25 MIPS Throughput with 25 MHz Clock

Expanded Interrupt Handler

MEMORY
-

256 Bytes Internal Data RAM

8k Bytes FLASH; In-System Programmable in 512 byte
Sectors

DIGITAL PERIPHERALS
-

8 Port I/O; All 5 V tolerant with High Sink Current

Hardware Enhanced UART and SMBusTM Serial Ports

Three General Purpose 16-Bit Counter/Timers

16-Bit Programmable Counter Array (PCA) with Three
Capture/Compare Modules

Real Time Clock Mode using PCA or Timer and External
Clock Source

CLOCK SOURCES
-

Internal Oscillator: 24.5 MHz with ±2% Accuracy Sup-
ports UART Operation

External Oscillator: Crystal, RC, C, or Clock (1 or 2 Pin
Modes)

Can Switch Between Clock Sources on-the-fly; Useful in
Power Saving Modes

11-PIN MICRO LEAD PACKAGE
-

3x3mm PWB Footprint; Actual MLP Size:

ANALOG

PERIPHERALS

8-bit

500ksps

ADC

PGA

8KB

ISP FLASH

256 B SRAM

POR

DEBUG

CIRCUITRY

INTERRUPTS

8051 CPU

(25MIPS)

TEMP

SENSOR

DIGITAL I/O

PROGRAMMABLE PRECISION INTERNAL

OSCILLATOR

HIGH-SPEED CONTROLLER CORE

U
X

ort

SSBAR

UART

SMBus

PCA

Timer 0

Timer 1

Timer 2

VOLTAGE

COMPARATOR

WDT

DS004-2.2 APR 03

Page 3

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

TABLE OF CONTENTS

1. SYSTEM OVERVIEW .........................................................................................................11

1.1. CIP-51TM Microcontroller Core ......................................................................................14

1.1.1. Fully 8051 Compatible ..........................................................................................14
1.1.2. Improved Throughput ............................................................................................14
1.1.3. Additional Features................................................................................................15

1.2. On-Chip Memory ............................................................................................................16
1.3. On-Chip Debug Circuitry ................................................................................................17
1.4. Programmable Digital I/O and Crossbar .........................................................................18
1.5. Serial Ports.......................................................................................................................18
1.6. Programmable Counter Array .........................................................................................19
1.7. 8-Bit Analog to Digital Converter (C8051F300/2 Only) ................................................20
1.8. Comparator ......................................................................................................................21

2. ABSOLUTE MAXIMUM RATINGS ..................................................................................22
3. GLOBAL DC ELECTRICAL CHARACTERISTICS ......................................................23
4. PINOUT AND PACKAGE DEFINITIONS........................................................................24
5. ADC0 (8-BIT ADC, C8051F300/2).......................................................................................31

5.1. Analog Multiplexer and PGA..........................................................................................32
5.2. Temperature Sensor.........................................................................................................33
5.3. Modes of Operation.........................................................................................................35

5.3.1. Starting a Conversion.............................................................................................35
5.3.2. Tracking Modes .....................................................................................................36
5.3.3. Settling Time Requirements ..................................................................................37

5.4. Programmable Window Detector ....................................................................................41

5.4.1. Window Detector In Single-Ended Mode .............................................................41
5.4.2. Window Detector In Differential Mode.................................................................42

6. VOLTAGE REFERENCE (C8051F300/2)..........................................................................45
7. COMPARATOR0 ..................................................................................................................47
8. CIP-51 MICROCONTROLLER..........................................................................................53

8.1. INSTRUCTION SET ......................................................................................................55

8.1.1. Instruction and CPU Timing..................................................................................55
8.1.2. MOVX Instruction and Program Memory.............................................................55

8.2. MEMORY ORGANIZATION........................................................................................59

8.2.1. Program Memory ...................................................................................................59
8.2.2. Data Memory .........................................................................................................60
8.2.3. General Purpose Registers .....................................................................................60
8.2.4. Bit Addressable Locations .....................................................................................60
8.2.5. Stack

...................................................................................................................61

8.2.6. Special Function Registers.....................................................................................61
8.2.7. Register Descriptions .............................................................................................64

8.3. Interrupt Handler .............................................................................................................67

8.3.1. MCU Interrupt Sources and Vectors .....................................................................67
8.3.2. External Interrupts .................................................................................................68
8.3.3. Interrupt Priorities..................................................................................................68

Page 4

DS004-2.2 APR 03

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

8.3.4. Interrupt Latency....................................................................................................68
8.3.5. Interrupt Register Descriptions ..............................................................................70

8.4. Power Management Modes .............................................................................................75

8.4.1. Idle Mode ...............................................................................................................75
8.4.2. Stop Mode..............................................................................................................75

9. RESET SOURCES ................................................................................................................77

9.1. Power-On Reset...............................................................................................................78
9.2. Power-Fail Reset / VDD Monitor....................................................................................78
9.3. External Reset..................................................................................................................79
9.4. Missing Clock Detector Reset .........................................................................................79
9.5. Comparator0 Reset ..........................................................................................................79
9.6. PCA Watchdog Timer Reset ...........................................................................................79
9.7. FLASH Error Reset .........................................................................................................79
9.8. Software Reset.................................................................................................................80

10. FLASH MEMORY ................................................................................................................83

10.1. Programming The FLASH Memory ...............................................................................83

10.1.1. FLASH Lock and Key Functions ..........................................................................83
10.1.2. FLASH Erase Procedure........................................................................................83
10.1.3. FLASH Write Procedure .......................................................................................84

10.2. Non-volatile Data Storage ...............................................................................................85
10.3. Security Options ..............................................................................................................85

11. OSCILLATORS.....................................................................................................................89

11.1. Programmable Internal Oscillator ...................................................................................89
11.2. External Oscillator Drive Circuit.....................................................................................91
11.3. System Clock Selection...................................................................................................91
11.4. External Crystal Example................................................................................................93
11.5. External RC Example ......................................................................................................93
11.6. External Capacitor Example............................................................................................93

12. PORT INPUT/OUTPUT .......................................................................................................95

12.1. Priority Crossbar Decoder ...............................................................................................96
12.2. Port I/O Initialization.......................................................................................................98
12.3. General Purpose Port I/O...............................................................................................101

13. SMBUS..................................................................................................................................103

13.1. Supporting Documents ..................................................................................................104
13.2. SMBus Configuration....................................................................................................104
13.3. SMBus Operation ..........................................................................................................105

13.3.1. Arbitration............................................................................................................105
13.3.2. Clock Low Extension...........................................................................................106
13.3.3. SCL Low Timeout ...............................................................................................106
13.3.4. SCL High (SMBus Free) Timeout.......................................................................106

13.4. Using the SMBus...........................................................................................................107

13.4.1. SMBus Configuration Register............................................................................108
13.4.2. SMB0CN Control Register ..................................................................................111
13.4.3. Data Register........................................................................................................114

13.5. SMBus Transfer Modes.................................................................................................115

DS004-2.2 APR 03

Page 5

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

13.5.1. Master Transmitter Mode ....................................................................................115
13.5.2. Master Receiver Mode.........................................................................................116
13.5.3. Slave Receiver Mode ...........................................................................................117
13.5.4. Slave Transmitter Mode.......................................................................................118

13.6. SMBus Status Decoding................................................................................................119

14. UART0 ..................................................................................................................................123

14.1. Enhanced Baud Rate Generation...................................................................................124
14.2. Operational Modes ........................................................................................................125

14.2.1. 8-Bit UART .........................................................................................................125
14.2.2. 9-Bit UART .........................................................................................................126

14.3. Multiprocessor Communications...................................................................................127

15. TIMERS................................................................................................................................133

15.1. Timer 0 and Timer 1......................................................................................................133

15.1.1. Mode 0: 13-bit Counter/Timer.............................................................................133
15.1.2. Mode 1: 16-bit Counter/Timer.............................................................................134
15.1.3. Mode 2: 8-bit Counter/Timer with Auto-Reload .................................................135
15.1.4. Mode 3: Two 8-bit Counter/Timers (Timer 0 Only) ...........................................136

15.2. Timer 2

.......................................................................................................................141

15.2.1. 16-bit Timer with Auto-Reload ...........................................................................141
15.2.2. 8-bit Timers with Auto-Reload............................................................................142

16. PROGRAMMABLE COUNTER ARRAY .......................................................................145

16.1. PCA Counter/Timer.......................................................................................................146
16.2. Capture/Compare Modules............................................................................................147

16.2.1. Edge-triggered Capture Mode .............................................................................148
16.2.2. Software Timer (Compare) Mode........................................................................149
16.2.3. High Speed Output Mode ....................................................................................150
16.2.4. Frequency Output Mode ......................................................................................151
16.2.5. 8-Bit Pulse Width Modulator Mode ....................................................................152
16.2.6. 16-Bit Pulse Width Modulator Mode ..................................................................153

16.3. Watchdog Timer Mode..................................................................................................154

16.3.1. Watchdog Timer Operation .................................................................................154
16.3.2. Watchdog Timer Usage .......................................................................................155

16.4. Register Descriptions for PCA ......................................................................................156

17. C2 INTERFACE ..................................................................................................................161

17.1. C2 Interface Registers ...................................................................................................161
17.2. C2 Pin Sharing...............................................................................................................163

DS004-2.2 APR 03

Page 7

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

LIST OF FIGURES AND TABLES

1. SYSTEM OVERVIEW

Table 1.1.

Product Selection Guide ......................................................................................12

Figure 1.1. C8051F300/2 Block Diagram..............................................................................12
Figure 1.2. C8051F301/3/4/5 Block Diagram .......................................................................13
Figure 1.3. Comparison of Peak MCU Execution Speeds.....................................................14
Figure 1.4. On-Chip Clock and Reset ....................................................................................15
Figure 1.5. On-chip Memory Map (C8051F300/1/2/3 shown)..............................................16
Figure 1.6. Development/In-System Debug Diagram ...........................................................17
Figure 1.7. Digital Crossbar Diagram....................................................................................18
Figure 1.8. PCA Block Diagram............................................................................................19
Figure 1.9. PCA Block Diagram............................................................................................19
Figure 1.10. 8-Bit ADC Block Diagram..................................................................................20
Figure 1.11. Comparator Block Diagram ................................................................................21

2. ABSOLUTE MAXIMUM RATINGS

Table 2.1.

Absolute Maximum Ratings*..............................................................................22

3. GLOBAL DC ELECTRICAL CHARACTERISTICS

Table 3.1.

Global DC Electrical Characteristics...................................................................23

4. PINOUT AND PACKAGE DEFINITIONS

Table 4.1.

Pin Definitions for the C8051F300/1/2/3/4/5......................................................24

Figure 4.1. MLP-11 Pinout Diagram (Top View) .................................................................25
Figure 4.2. MLP-11 Package Drawing ..................................................................................26
Table 4.2.

MLP-11 Package Diminsions..............................................................................26

Figure 4.3. Typical MLP-11 Solder Mask .............................................................................27
Figure 4.4. Typical MLP-11 Landing Diagram .....................................................................28

5. ADC0 (8-BIT ADC, C8051F300/2)

Figure 5.1. ADC0 Functional Block Diagram .......................................................................31
Figure 5.2. Typical Temperature Sensor Transfer Function..................................................33
Figure 5.3. Temperature Sensor Error with 1-Point Calibration (VREF = 2.40 V) ..............34
Figure 5.4. 8-Bit ADC Track and Conversion Example Timing...........................................36
Figure 5.5. ADC0 Equivalent Input Circuits .........................................................................37
Figure 5.6. AMX0SL: AMUX0 Channel Select Register (C8051F300/2)............................38
Figure 5.7. ADC0CF: ADC0 Configuration Register (C8051F300/2)..................................39
Figure 5.8. ADC0: ADC0 Data Word Register (C8051F300/2) ...........................................39
Figure 5.9. ADC0CN: ADC0 Control Register (C8051F300/2) ...........................................40
Figure 5.10. ADC Window Compare Examples, Single-Ended Mode ...................................41
Figure 5.11. ADC Window Compare Examples, Differential Mode ......................................42
Figure 5.12. ADC0GT: ADC0 Greater-Than Data Byte Register (C8051F300/2) .................43
Figure 5.13. ADC0LT: ADC0 Less-Than Data Byte Register (C8051F300/2) ......................43
Table 5.1.

ADC0 Electrical Characteristics..........................................................................44

6. VOLTAGE REFERENCE (C8051F300/2)

Figure 6.1. Voltage Reference Functional Block Diagram....................................................45
Figure 6.2. REF0CN: Reference Control Register ................................................................46
Table 6.1.

External Voltage Reference Circuit Electrical Characteristics ...........................46

Page 8

DS004-2.2 APR 03

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

7. COMPARATOR0

Figure 7.1. Comparator0 Functional Block Diagram ............................................................47
Figure 7.2. Comparator Hysteresis Plot .................................................................................48
Figure 7.3. CPT0CN: Comparator0 Control Register ...........................................................49
Figure 7.4. CPT0MX: Comparator0 MUX Selection Register..............................................50
Figure 7.5. CPT0MD: Comparator0 Mode Selection Register..............................................51
Table 7.1.

Comparator0 Electrical Characteristics ...............................................................52

8. CIP-51 MICROCONTROLLER

Figure 8.1. CIP-51 Block Diagram ........................................................................................53
Table 8.1.

CIP-51 Instruction Set Summary.........................................................................55

Figure 8.2. Program Memory Maps.......................................................................................59
Figure 8.3. Data Memory Map ..............................................................................................60
Table 8.2.

Special Function Register (SFR) Memory Map..................................................62

Table 8.3.

Special Function Registers ..................................................................................62

Figure 8.4. DPL: Data Pointer Low Byte ..............................................................................64
Figure 8.5. DPH: Data Pointer High Byte .............................................................................64
Figure 8.6. SP: Stack Pointer .................................................................................................65
Figure 8.7. PSW: Program Status Word ................................................................................65
Figure 8.8. ACC: Accumulator..............................................................................................66
Figure 8.9. B: B Register .......................................................................................................66
Table 8.4.

Interrupt Summary...............................................................................................69

Figure 8.10. IE: Interrupt Enable .............................................................................................70
Figure 8.11. IP: Interrupt Priority ............................................................................................71
Figure 8.12. EIE1: Extended Interrupt Enable 1 .....................................................................72
Figure 8.13. EIP1: Extended Interrupt Priority 1.....................................................................73
Figure 8.14. IT01CF: INT0/INT1 Configuration Register ......................................................74
Figure 8.15. PCON: Power Control Register ..........................................................................76

9. RESET SOURCES

Figure 9.1. Reset Sources.......................................................................................................77
Figure 9.2. Power-On and VDD Monitor Reset Timing .......................................................78
Table 9.1.

User Code Space Address Limits ........................................................................79

Table 9.2.

Reset Electrical Characteristics ...........................................................................80

Figure 9.3. RSTSRC: Reset Source Register.........................................................................81

10. FLASH MEMORY

Table 10.1. FLASH Electrical Characteristics .......................................................................84
Table 10.2. Security Byte Decoding.......................................................................................85
Figure 10.1. FLASH Program Memory Map ..........................................................................85
Figure 10.2. PSCTL: Program Store R/W Control ..................................................................86
Figure 10.3. FLKEY: FLASH Lock and Key Register ...........................................................87
Figure 10.4. FLSCL: FLASH Scale Register ..........................................................................87

11. OSCILLATORS

Figure 11.1. Oscillator Diagram ..............................................................................................89
Figure 11.2. OSCICL: Internal Oscillator Calibration Register ..............................................90
Figure 11.3. OSCICN: Internal Oscillator Control Register ...................................................90
Table 11.1. Internal Oscillator Electrical Characteristics.......................................................91

DS004-2.2 APR 03

Page 9

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

Figure 11.4. OSCXCN: External Oscillator Control Register.................................................92

12. PORT INPUT/OUTPUT

Figure 12.1. Port I/O Functional Block Diagram ....................................................................95
Figure 12.2. Port I/O Cell Block Diagram...............................................................................95
Figure 12.3. Crossbar Priority Decoder with XBR0 = 0x00 ...................................................96
Figure 12.4. Crossbar Priority Decoder with XBR0 = 0x44 ...................................................97
Figure 12.5. XBR0: Port I/O Crossbar Register 0 ...................................................................99
Figure 12.6. XBR1: Port I/O Crossbar Register 1 ...................................................................99
Figure 12.7. XBR2: Port I/O Crossbar Register 2 .................................................................100
Figure 12.8. P0: Port0 Register..............................................................................................101
Figure 12.9. P0MDIN: Port0 Input Mode Register ...............................................................101
Figure 12.10. P0MDOUT: Port0 Output Mode Register.......................................................102
Table 12.1. Port I/O DC Electrical Characteristics ..............................................................102

13. SMBUS

Figure 13.1. SMBus Block Diagram .....................................................................................103
Figure 13.2. Typical SMBus Configuration ..........................................................................104
Figure 13.3. SMBus Transaction ...........................................................................................105
Table 13.1. SMBus Clock Source Selection.........................................................................108
Figure 13.4. Typical SMBus SCL Generation.......................................................................108
Table 13.2. Minimum SDA Setup and Hold Times .............................................................109
Figure 13.5. SMB0CF: SMBus Clock/Configuration Register .............................................110
Figure 13.6. SMB0CN: SMBus Control Register .................................................................112
Table 13.3. Sources for Hardware Changes to SMB0CN ....................................................113
Figure 13.7. SMB0DAT: SMBus Data Register ...................................................................114
Figure 13.8. Typical Master Transmitter Sequence...............................................................115
Figure 13.9. Typical Master Receiver Sequence ...................................................................116
Figure 13.10. Typical Slave Receiver Sequence ...................................................................117
Figure 13.11. Typical Slave Transmitter Sequence ...............................................................118
Table 13.4. SMBus Status Decoding....................................................................................119

14. UART0

Figure 14.1. UART0 Block Diagram.....................................................................................123
Figure 14.2. UART0 Baud Rate Logic ..................................................................................124
Figure 14.3. UART Interconnect Diagram ............................................................................125
Figure 14.4. 8-Bit UART Timing Diagram ...........................................................................125
Figure 14.5. 9-Bit UART Timing Diagram ...........................................................................126
Figure 14.6. UART Multi-Processor Mode Interconnect Diagram .......................................127
Figure 14.7. SCON0: Serial Port 0 Control Register.............................................................128
Figure 14.8. SBUF0: Serial (UART0) Port Data Buffer Register .........................................129
Table 14.1. Timer Settings for Standard Baud Rates Using The Internal Oscillator ...........130
Table 14.2. Timer Settings for Standard Baud Rates Using an External Oscillator.............130
Table 14.3. Timer Settings for Standard Baud Rates Using an External Oscillator.............131
Table 14.4. Timer Settings for Standard Baud Rates Using an External Oscillator.............131
Table 14.5. Timer Settings for Standard Baud Rates Using an External Oscillator.............132
Table 14.6. Timer Settings for Standard Baud Rates Using an External Oscillator.............132

15. TIMERS

Page 10

DS004-2.2 APR 03

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

Figure 15.1. T0 Mode 0 Block Diagram................................................................................134
Figure 15.2. T0 Mode 2 Block Diagram................................................................................135
Figure 15.3. T0 Mode 3 Block Diagram................................................................................136
Figure 15.4. TCON: Timer Control Register.........................................................................137
Figure 15.5. TMOD: Timer Mode Register...........................................................................138
Figure 15.6. CKCON: Clock Control Register......................................................................139
Figure 15.7. TL0: Timer 0 Low Byte ....................................................................................140
Figure 15.8. TL1: Timer 1 Low Byte ....................................................................................140
Figure 15.9. TH0: Timer 0 High Byte ...................................................................................140
Figure 15.10. TH1: Timer 1 High Byte .................................................................................140
Figure 15.11. Timer 2 16-Bit Mode Block Diagram .............................................................141
Figure 15.12. Timer 2 8-Bit Mode Block Diagram ...............................................................142
Figure 15.13. TMR2CN: Timer 2 Control Register ..............................................................143
Figure 15.14. TMR2RLL: Timer 2 Reload Register Low Byte ............................................144
Figure 15.15. TMR2RLH: Timer 2 Reload Register High Byte ...........................................144
Figure 15.16. TMR2L: Timer 2 Low Byte ............................................................................144
Figure 15.17. TMR2H Timer 2 High Byte ............................................................................144

16. PROGRAMMABLE COUNTER ARRAY

Figure 16.1. PCA Block Diagram..........................................................................................145
Figure 16.2. PCA Counter/Timer Block Diagram .................................................................146
Table 16.1. PCA Timebase Input Options............................................................................146
Figure 16.3. PCA Interrupt Block Diagram...........................................................................147
Table 16.2. PCA0CPM Register Settings for PCA Capture/Compare Modules..................147
Figure 16.4. PCA Capture Mode Diagram ............................................................................148
Figure 16.5. PCA Software Timer Mode Diagram................................................................149
Figure 16.6. PCA High Speed Output Mode Diagram ..........................................................150
Figure 16.7. PCA Frequency Output Mode ...........................................................................151
Figure 16.8. PCA 8-Bit PWM Mode Diagram ......................................................................152
Figure 16.9. PCA 16-Bit PWM Mode ...................................................................................153
Figure 16.10. PCA Module 2 with Watchdog Timer Enabled ..............................................154
Table 16.3. Watchdog Timer Timeout Intervals ................................................................155
Figure 16.11. PCA0CN: PCA Control Register ....................................................................156
Figure 16.12. PCA0MD: PCA Mode Register ......................................................................157
Figure 16.13. PCA0CPMn: PCA Capture/Compare Mode Registers ...................................158
Figure 16.14. PCA0L: PCA Counter/Timer Low Byte .........................................................159
Figure 16.15. PCA0H: PCA Counter/Timer High Byte ........................................................159
Figure 16.16. PCA0CPLn: PCA Capture Module Low Byte ................................................160
Figure 16.17. PCA0CPHn: PCA Capture Module High Byte ...............................................160

17. C2 INTERFACE

Figure 17.1. C2ADD: C2 Address Register ..........................................................................161
Figure 17.2. DEVICEID: C2 Device ID Register .................................................................161
Figure 17.3. REVID: C2 Revision ID Register .....................................................................162
Figure 17.4. FPCTL: C2 FLASH Programming Control Register ........................................162
Figure 17.5. FPDAT: C2 FLASH Programming Data Register ............................................162
Figure 17.6. Typical C2 Pin Sharing .....................................................................................163

DS004-2.2 APR 03

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PRELIMINARY

C8051F300/1/2/3

C8051F304/5

SYSTEM OVERVIEW

C8051F300/1/2/3/4/5 devices are fully integrated mixed-signal System-on-a-Chip MCUs. Highlighted features are
listed below. Refer to Table 1.1 on page 12 for specific product feature selection.

High-speed pipelined 8051-compatible microcontroller core (up to 25 MIPS)

In-system, full-speed, non-intrusive debug interface (on-chip)

True 8-bit 500 ksps 11-channel ADC with programmable gain pre-amplifier and analog multiplexer

Precision programmable 25 MHz internal oscillator

2/4/8k bytes of on-chip FLASH memory

256 bytes of on-chip RAM

SMBus/I

C and Enhanced UART serial interfaces implemented in hardware

Three general-purpose 16-bit timers

Programmable Counter/Timer Array (PCA) with three capture/compare modules and Watchdog Timer function

On-chip Power-On Reset, VDD Monitor, and Temperature Sensor

On-chip Voltage Comparator

Byte-wide I/O Port (5V tolerant)

With on-chip Power-On Reset, VDD monitor, Watchdog Timer, and clock oscillator, the C8051F300/1/2/3/4/5
devices are truly stand-alone System-on-a-Chip solutions. The FLASH memory can be reprogrammed even in-cir-
cuit, providing non-volatile data storage, and also allowing field upgrades of the 8051 firmware. User software has
complete control of all peripherals, and may individually shut down any or all peripherals for power savings.

The on-chip Cygnal 2-Wire (C2) Development Interface allows non-intrusive (uses no on-chip resources), full speed,
in-circuit debugging using the production MCU installed in the final application. This debug logic supports inspec-
tion and modification of memory and registers, setting breakpoints, single stepping, run and halt commands. All ana-
log and digital peripherals are fully functional while debugging using C2. The two C2 interface pins can be shared
with user functions, allowing in-system debugging without occupying package pins.

Each device is specified for 2.7 V-to-3.6 V operation over the industrial temperature range (-45°C to +85°C). The
Port I/O and /RST pins are tolerant of input signals up to 5 V. The C8051F300/1/2/3/4/5 are available in the 11-pin
MLP package shown in Figure 4.2.

Page 12

DS004-2.2 APR 03

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

Table 1.1. Product Selection Guide

(Peak)

ASH

r
y

Cali

r
ated

I
n

ter

s
cillat

SMB

s
/
I

UAR

i
mer

(
16-

t
)

r
o

ramm

abl

t
e
r

rray

Dig

ital

r
t

I
/O

i
t

e
mp

eratur

s
o

arators

Packag

C8051F300

256

MLP-11

C8051F301

256

MLP-11

C8051F302

256

MLP-11

C8051F303

256

MLP-11

C8051F304

256

MLP-11

C8051F305

256

MLP-11

Figure 1.1. C8051F300/2 Block Diagram

Port 0

Latch

UART

8kbyte

FLASH

256 byte

SRAM

POR

SFR Bus

8
0
5
1

Timer 0, 1

PCA/
WDT

8-bit
500ksps
ADC

M
U

AIN0-AIN7

VREF

X
B
A
R

Port I/O Mode

& Config.

XBAR

Control

Reset

XTAL1

XTAL2

External

Oscillator

Circuit

System Clock

Precision

Internal

Oscillator

Clock & Reset

Configuration

Analog/Digital

Power

Debug HW

VDD

ADC

Config. &

Control

SMBus

C2D

CP0

PGA

Temp

CP0

P0.0/VREF

P0.1

P0.2/XTAL1

P0.3/XTAL2

P0.4/TX

P0.5/RX

P0.6/CNVSTR

P0.7/C2D

VDD

GND

/RST/C2CK

Brown-

Out

VDD

CNVSTR

Page 14

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PRELIMINARY

C8051F300/1/2/3

C8051F304/5

1.1.

CIP-51TM Microcontroller Core

1.1.1.

Fully 8051 Compatible

The C8051F300/1/2/3/4/5 family utilizes Cygnal's proprietary CIP-51 microcontroller core. The CIP-51 is fully com-
patible with the MCS-51TM instruction set; standard 803x/805x assemblers and compilers can be used to develop soft-
ware. The CIP-51 core offers all the peripherals included with a standard 8052, including two standard 16-bit
counter/timers, one enhanced 16-bit counter/timer with external oscillator input, a full-duplex UART with extended
baud rate configuration, 256 bytes of internal RAM, 128 byte Special Function Register (SFR) address space, and a
byte-wide I/O Port.

1.1.2.

Improved Throughput

The CIP-51 employs a pipelined architecture that greatly increases its instruction throughput over the standard 8051
architecture. In a standard 8051, all instructions except for MUL and DIV take 12 or 24 system clock cycles to exe-
cute with a maximum system clock of 12-to-24 MHz. By contrast, the CIP-51 core executes 70% of its instructions in
one or two system clock cycles, with only four instructions taking more than four system clock cycles.

The CIP-51 has a total of 109 instructions. The table below shows the total number of instrutions that require each
execution time.

With the CIP-51's maximum system clock at 25 MHz, it has a peak throughput of 25 MIPS. Figure 1.3 shows a com-
parison of peak throughputs for various 8-bit microcontroller cores with their maximum system clocks.

Clocks to Execute

2/3

3/4

4/5

Number of Instructions

ADuC812

8051

(16MHz clk)

Philips

80C51

(33MHz clk)

Microchip

PIC17C75x

(33MHz clk)

Cygnal
CIP-51

(25MHz clk)

Figure 1.3. Comparison of Peak MCU Execution Speeds

DS004-2.2 APR 03

Page 15

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

1.1.3.

Additional Features

The C8051F300/1/2/3/4/5 SoC family includes several key enhancements to the CIP-51 core and peripherals to
improve performance and ease of use in end applications.

The extended interrupt handler provides 12 interrupt sources into the CIP-51 (as opposed to 7 for the standard 8051),
allowing numerous analog and digital peripherals to interrupt the controller. An interrupt driven system requires less
intervention by the MCU, giving it more effective throughput. The extra interrupt sources are very useful when build-
ing multi-tasking, real-time systems.

Eight reset sources are available: power-on reset circuitry (POR), an on-chip VDD monitor (forces reset when power
supply voltage drops below 2.7 V), a Watchdog Timer, a Missing Clock Detector, a voltage level detection from
Comparator0, a forced software reset, an external reset pin, and an illegal FLASH read/write protection circuit. Each
reset source except for the POR, Reset Input Pin, or FLASH protection may be disabled by the user in software. The
WDT may be permanently enabled in software after a power-on reset during MCU initialization.

The internal oscillator is available as a factory calibrated 24.5 MHz ±2% (C8051F300/1 devices); an uncalibrated
version is available on C8051F302/3/4/5 devices. On all C8051F300/1/2/3/4/5 devices, the internal oscillator period
may be user programmed in ~0.5% increments. An external oscillator drive circuit is also included, allowing an
external crystal, ceramic resonator, capacitor, RC, or CMOS clock source to generate the system clock. If desired, the
system clock source may be switched on-the-fly to the external oscillator circuit. An external oscillator can be
extremely useful in low power applications, allowing the MCU to run from a slow (power saving) external crystal
source, while periodically switching to the fast (up to 25 MHz) internal oscillator as needed.

PCA

WDT

Missing

Clock

Detector

(one-

shot)

(Software Reset)

System Reset

Reset
Funnel

P0.x

P0.y

SWRSF

Internal

Oscillator

System
Clock

CIP-51

Microcontroller

Core

Extended Interrupt

Handler

Clock Select

WDT

Ena

l
e

MCD

Ena

l
e

XTAL1

XTAL2

External

Oscillator

Drive

Illegal

FLASH

Operation

+
-

Comparator 0

C0RSEF

/RST

(wired-OR)

Power On

Reset

+
-

VDD

Supply
Monitor

Enable

'0'

Figure 1.4. On-Chip Clock and Reset

Page 16

DS004-2.2 APR 03

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

1.2.

On-Chip Memory

The CIP-51 has a standard 8051 program and data address configuration. It includes 256 bytes of data RAM, with the
upper 128 bytes dual-mapped. Indirect addressing accesses the upper 128 bytes of general purpose RAM, and direct
addressing accesses the 128 byte SFR address space. The lower 128 bytes of RAM are accessible via direct and indi-
rect addressing. The first 32 bytes are addressable as four banks of general purpose registers, and the next 16 bytes
can be byte addressable or bit addressable.

The C8051F300/1/2/3 includes 8k bytes of FLASH program memory (the C8051F304 includes 4k bytes; the
C8051F305 includes 2k bytes). This memory may be reprogrammed in-system in 512 byte sectors, and requires no
special off-chip programming voltage. See Figure 1.5 for the C8051F300/1/2/3 system memory map.

PROGRAM MEMORY

(Direct and Indirect

Addressing)

0x00

0x7F

Upper 128 RAM

(Indirect Addressing

Only)

0x80

0xFF

Special Function

(Direct Addressing Only)

DATA MEMORY

General Purpose

Registers

0x1F

0x20

0x2F

Bit Addressable

Lower 128 RAM
(Direct and Indirect
Addressing)

0x30

INTERNAL DATA ADDRESS SPACE

8k bytes

FLASH

(In-System

Programmable in 512

Byte Sectors)

0x0000

RESERVED

0x1E00

0x1DFF

Figure 1.5. On-chip Memory Map (C8051F300/1/2/3 shown)

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Page 17

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

1.3.

On-Chip Debug Circuitry

The C8051F300/1/2/3/4/5 devices include on-chip Cygnal 2-Wire (C2) debug circuitry that provides non-intrusive,
full speed, in-circuit debugging of the production part installed in the end application.

Cygnal's debugging system supports inspection and modification of memory and registers, breakpoints, and single
stepping. No additional target RAM, program memory, timers, or communications channels are required. All the dig-
ital and analog peripherals are functional and work correctly while debugging. All the peripherals (except for the
ADC and SMBus) are stalled when the MCU is halted, during single stepping, or at a breakpoint in order to keep
them synchronized.

The C8051F300DK development kit provides all the hardware and software necessary to develop application code
and perform in-circuit debugging with the C8051F300/1/2/3/4/5 MCUs. The kit includes software with a developer's
studio and debugger, an integrated 8051 assembler, and an RS-232 to C2 serial adapter. It also has a target application
board with the associated MCU installed and large prototyping area, plus the RS-232 and C2 cables, and wall-mount
power supply. The Development Kit requires a Windows 95/98/NT/ME/2000 computer with one available RS-232
serial port. As shown in Figure 1.6, the PC is connected via RS-232 to the Serial Adapter. A six-inch ribbon cable
connects the Serial Adapter to the user's application board, picking up the two C2 pins and VDD and GND. The
Serial Adapter takes its power from the application board; it requires roughly 20 mA at 2.7-3.6V. For applications
where there is not sufficient power available from the target board, the provided power supply can be connected
directly to the Serial Adapter.

The Cygnal IDE interface is a vastly superior developing and debugging configuration, compared to standard MCU
emulators that use on-board "ICE Chips" and require the MCU in the application board to be socketed. Cygnal's
debug paradigm increases ease of use and preserves the performance of the precision analog peripherals.

TARGET PCB

RS-232

Serial

Adapter

VDD

GND

C2 (x2), VDD, GND

WINDOWS 95/98/NT/ME/2000

CYGNAL Integrated

Development Environment

C8051F300

Figure 1.6. Development/In-System Debug Diagram

Page 18

DS004-2.2 APR 03

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

1.4.

Programmable Digital I/O and Crossbar

C8051F300/1/2/3/4/5 devices include a byte-wide I/O Port that behaves like a typical 8051 Port with a few enhance-
ments. Each Port pin may be configured as an analog input or a digital I/O pin. Pins selected as digital I/Os may addi-
tionally be configured for push-pull or open-drain output. The "weak pull-ups" that are fixed on typical 8051 devices
may be globally disabled, providing power savings capabilities.

Perhaps the most unique Port I/O enhancement is the Digital Crossbar. This is essentially a digital switching network
that allows mapping of internal digital system resources to Port I/O pins (See Figure 1.7). On-chip counter/timers,
serial buses, HW interrupts, comparator output, and other digital signals in the controller can be configured to appear
on the Port I/O pins specified in the Crossbar Control registers. This allows the user to select the exact mix of general
purpose Port I/O and digital resources needed for the particular application.

1.5.

Serial Ports

The C8051F300/1/2/3/4/5 Family includes an SMBus/I

C interface and a full-duplex UART with enhanced baud rate

configuration. Each of the serial buses is fully implemented in hardware and makes extensive use of the CIP-51's
interrupts, thus requiring very little CPU intervention.

Figure 1.7. Digital Crossbar Diagram

XBR0, XBR1,

XBR2 Registers

Digital

Crossbar

Priority

Decoder

SYSCLK

t
e

r
nal

i
gital

nals

)

Highest

Priority

Lowest

Priority

I/O

Cells

P0.0

P0.7

P0MDOUT,

P0MDIN Registers

SMBus

UART

T0, T1

PCA

Port Latch

(P0.0-P0.7)

CP0

Outputs

DS004-2.2 APR 03

Page 19

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

1.6.

Programmable Counter Array

An on-chip Programmable Counter/Timer Array (PCA) is included in addition to the three 16-bit general purpose
counter/timers. The PCA consists of a dedicated 16-bit counter/timer time base with three programmable cap-
ture/compare modules. The PCA clock is derived from one of six sources: the system clock divided by 12, the system
clock divided by 4, Timer 0 overflows, an External Clock Input (ECI), the system clock, or the external oscillator
clock source divided by 8. The external clock source selection is useful for real-time clock functionality, where the
PCA is clocked by an external source while the internal oscillator drives the system clock.

Each capture/compare module can be configured to operate in one of six modes: Edge-Triggered Capture, Software
Timer, High Speed Output, 8- or 16-bit Pulse Width Modulator, or Frequency Output. Additionally, Capture/Compare
Module 2 offers watchdog timer (WDT) capabilities. Following a system reset, Module 2 is configured and enabled
in WDT mode. The PCA Capture/Compare Module I/O and External Clock Input may be routed to Port I/O via the
Digital Crossbar.

16-Bit Counter/Timer

CE
X1

ECI

Digital Crossbar

EX2

EX0

Port I/O

Capture/Compare

Module 1

Capture/Compare

Module 0

Capture/Compare

Module 2

PCA

CLOCK

MUX

SYSCLK/12

SYSCLK/4

Timer 0 Overflow

ECI

SYSCLK

External Clock/8

Figure 1.8. PCA Block Diagram

Page 20

DS004-2.2 APR 03

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

1.7.

8-Bit Analog to Digital Converter (C8051F300/2 Only)

The C8051F300/2 includes an on-chip 8-bit SAR ADC with a 10-channel differential input multiplexer and program-
mable gain amplifier. With a maximum throughput of 500 ksps, the ADC offers true 8-bit accuracy with an INL of
±1LSB. The ADC system includes a configurable analog multiplexer that selects both positive and negative ADC
inputs. Each Port pin is available as an ADC input; additionally, the on-chip Temperature Sensor output and the
power supply voltage (VDD) are available as ADC inputs. User firmware may shut down the ADC to save power.

The integrated programmable gain amplifier (PGA) amplifies the the ADC input by 0.5, 1, 2, or 4 as defined by user
software. The gain stage is especially useful when different ADC input channels have widely varied input voltage
signals, or when it is necessary to "zoom in" on a signal with a large DC offset.

Conversions can be started in five ways: a software command, an overflow of Timer 0, 1, or 2, or an external convert
start signal. This flexibility allows the start of conversion to be triggered by software events, a periodic signal (timer
overflows), or external HW signals. Conversion completions are indicated by a status bit and an interrupt (if enabled).
The resulting 8-bit data word is latched into an SFR upon completion of a conversion.

Window compare registers for the ADC data can be configured to interrupt the controller when ADC data is either
within or outside of a specified range. The ADC can monitor a key voltage continuously in background mode, but not
interrupt the controller unless the converted data is within/outside the specified range.

Figure 1.9. 8-Bit ADC Block Diagram

VDD

9-to-1

AMUX

Temp

Sensor

10-to-1

AMUX

VDD

P0.0

P0.1

P0.2

P0.3

P0.4

P0.5

P0.6

P0.7

P0.0

P0.1

P0.2

P0.3

P0.4

P0.5

P0.6

P0.7

DGND

Programmable Gain

Amplifier

Start

Conversion

Window Compare

Logic

Window
Compare
Interrupt

+
-

Configuration, Control, and Data Registers

Analog Multiplexer

T0 Overflow

TMR2 Overflow

T1 Overflow

Software Write

External
Convert Start

8-Bit
SAR

ADC

End of
Conversion
Interrupt

ADC Data

Page 24

DS004-2.2 APR 03

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

PINOUT AND PACKAGE DEFINITIONS

Table 4.1. Pin Definitions for the C8051F300/1/2/3/4/5

Pin Number

Name

Type

Description

VREF /

P0.0

A In

D I/O or
A In

External Voltage Reference Input.

Port 0.0. See

Section 12

for complete description.

P0.1

D I/O or
A In

Port 0.1. See

Section 12

for complete description.

VDD

Power Supply Voltage.

XTAL1 /

P0.2

A In

D I/O or
A In

Crystal Input. This pin is the external oscillator circuit return for a
crystal or ceramic resonator. See

Section 11.2

Port 0.2. See

Section 12

for complete description.

XTAL2 /

P0.3

A Out

D I/O

Crystal Input/Output. For an external crystal or resonator, this pin
is the excitation driver. This pin is the external clock input for
CMOS, capacitor, or RC network configurations. See

Section

11.2

Port 0.3. See

Section 12

for complete description.

P0.4

D I/O or
A In

Port 0.4. See

Section 12

for complete description.

P0.5

D I/O or
A In

Port 0.5. See

Section 12

for complete description.

C2CK /

/RST

D I/O

Clock signal for the C2 Development Interface.

Device Reset. Open-drain output of internal POR or VDD moni-
tor. An external source can initiate a system reset by driving this
pin low for at least 10 µs.

P0.6 /

CNVSTR

D I/O or
A In

D I/O

Port 0.6. See

Section 12

for complete description.

ADC External Convert Start Input Strobe.

C2D /

P0.7

D I/O

D I/O or
A In

Data signal for the C2 Development Interface.

Port 0.7. See

Section 12

for complete description.

GND

Ground.

DS004-2.2 APR 03

Page 31

PRELIMINARY

C8051F300/2

ADC0 (8-BIT ADC, C8051F300/2)

The ADC0 subsystem for the C8051F300/2 consists of two analog multiplexers (referred to collectively as AMUX0)
with 11 total input selections, a differential programmable gain amplifier (PGA), and a 500 ksps, 8-bit successive-
approximation-register ADC with integrated track-and-hold and programmable window detector (see block diagram
in Figure 5.1). The AMUX0, PGA, data conversion modes, and window detector are all configurable under software
control via the Special Function Registers shown in Figure 5.1. ADC0 operates in both Single-ended and Differential
modes, and may be configured to measure any Port pin, the Temperature Sensor output, or VDD with respect to any
Port pin or GND. The ADC0 subsystem is enabled only when the AD0EN bit in the ADC0 Control register
(ADC0CN) is set to logic 1. The ADC0 subsystem is in low power shutdown when this bit is logic 0.

Figure 5.1. ADC0 Functional Block Diagram

AMUX0

+
-

VDD

ADC0CF

8-Bit
SAR

ADC

SYSC

ADC

ADC0CN

I
N

Timer 0 Overflow

Timer 2 Overflow

Timer 1 Overflow

Start

Conversion

000

AD0BUSY (W)

VDD

ADC0GT

ADC0LT

9-to-1

AMUX

AD0WINT

Temp

Sensor

10-to-1

AMUX

VDD

P0.0

P0.1

P0.2

P0.3

P0.4

P0.5

P0.6

P0.7

P0.0

P0.1

P0.2

P0.3

P0.4

P0.5

P0.6

P0.7

GND

001

010

011

1xx

CNVSTR Input

Comb.

Logic

AMX0SL

Page 32

DS004-2.2 APR 03

PRELIMINARY

C8051F300/2

5.1.

Analog Multiplexer and PGA

The analog multiplexers (AMUX0) select the positive and negative inputs to the PGA, allowing any Port pin to be
measured relative to any other Port pin or GND. Additionally, the on-chip temperature sensor or the positive power
supply (VDD) may be selected as the positive PGA input. When GND is selected as the negative input, ADC0
operates in Single-ended Mode; all other times, ADC0 operates in Differential Mode. The ADC0 input channels
are selected in the AMX0SL register as described in Figure 5.6.

The conversion code format differs in Single-ended versus Differential modes, as shown below. When in Single-
ended Mode (negative input is selected GND), conversion codes are represented as 8-bit unsigned integers. Inputs are
measured from `0' to VREF * 255/256. Example codes are shown below.

When in Differential Mode (negative input is not selected as GND), conversion codes are represented as 8-bit signed
2's complement numbers. Inputs are measured from -VREF to VREF * 127/128. Example codes are shown below.

Important Note About ADC0 Input Configuration: Port pins selected as ADC0 inputs should be configured as
analog inputs and should be skipped by the Digital Crossbar. To configure a Port pin for analog input, set to `0' the
corresponding bit in register P0MDIN. To force the Crossbar to skip a Port pin, set to `1' the corresponding bit in reg-
ister XBR0. See

Section "12. Port Input/Output" on page 95

for more Port I/O configuration details.

The PGA amplifies the AMUX0 output signal as defined by the AMP0GN1-0 bits in the ADC0 Configuration regis-
ter (Figure 5.7). The PGA is software-programmable for gains of 0.5, 1, 2, or 4. The gain defaults to 0.5 on reset.

Input Voltage

ADC0 Output (Conversion Code)

VREF * 255/256

0xFF

VREF * 128/256

0x80

VREF * 64/256

0x40

0x00

Input Voltage

ADC0 Output (Conversion Code)

VREF * 127/128

0x7F

VREF * 64/128

0x40

0x00

-VREF * 64/128

0xC0

- VREF

0x80

DS004-2.2 APR 03

Page 33

PRELIMINARY

C8051F300/2

5.2.

Temperature Sensor

The typical temperature sensor transfer function is shown in Figure 5.2. The output voltage (V

TEMP

) is the positive

PGA input when the temperature sensor is selected by bits AMX0P2-0 in register AMX0SL; this voltage will be
amplified by the PGA according to the user-programmed PGA settings.

The uncalibrated temperature sensor output is extremely linear and suitable for relative temperature measurements
(see Table 5.1 for linearity specifications). For absolute temperature measurements, gain and/or offset calibration is
recommended. Typically a 1-point calibration includes the following steps:

Step 1. Control/measure the ambient temperature (this temperature must be known).
Step 2. Power the device, and delay for a few seconds to allow for self-heating.
Step 3. Perform an ADC conversion with the temperature sensor selected as the positive input and GND

selected as the negative input.

Step 4. Calculate the offset and/or gain characteristics, and store these values in non-volatile memory for

use with subsequent temperature sensor measurements.

Figure 5.3 shows the typical temperature sensor error assuming a 1-point calibration at 25 °C. Note that parameters
which affect ADC measurement, in particular the voltage reference value, will also affect temperature mea-
surement.

Figure 5.2. Typical Temperature Sensor Transfer Function

-50

100

(Celsius)

TEMP

= 3.35*(TEMP

) + 897 mV

700

800

900

1000

1100

(mV)

1200

DS004-2.2 APR 03

Page 35

PRELIMINARY

C8051F300/2

5.3.

Modes of Operation

ADC0 has a maximum conversion speed of 500 ksps. The ADC0 conversion clock is a divided version of the system
clock, determined by the AD0SC bits in the ADC0CF register (system clock divided by (AD0SC + 1) for
0

AD0SC 31).

5.3.1.

Starting a Conversion

A conversion can be initiated in one of five ways, depending on the programmed states of the ADC0 Start of Conver-
sion Mode bits (AD0CM2-0) in register ADC0CN. Conversions may be initiated by one of the following:

Writing a `1' to the AD0BUSY bit of register ADC0CN

A Timer 0 overflow (i.e. timed continuous conversions)

A Timer 2 overflow

A Timer 1 overflow

A rising edge on the CNVSTR input signal (pin P0.6)

Writing a `1' to AD0BUSY provides software control of ADC0 whereby conversions are performed "on-demand".
During conversion, the AD0BUSY bit is set to logic 1 and reset to logic 0 when the conversion is complete. The fall-
ing edge of AD0BUSY triggers an interrupt (when enabled) and sets the ADC0 interrupt flag (AD0INT). Note: When
polling for ADC conversion completions, the ADC0 interrupt flag (AD0INT) should be used. Converted data is avail-
able in the ADC0 data register, ADC0, when bit AD0INT is logic 1. Note that when Timer 2 overflows are used as
the conversion source, Timer 2 Low Byte overflows are used if Timer 2 is in 8-bit mode; Timer 2 High byte over-
flows are used if Timer 2 is in 16-bit mode. See

Section "15. Timers" on page 133

for timer configuration.

Important Note About Using CNVSTR: The CNVSTR input pin also functions as Port pin P0.6. When the
CNVSTR input is used as the ADC0 conversion source, Port pin P0.6 should be skipped by the Digital Crossbar. To
configure the Crossbar to skip P0.6, set to `1' Bit6 in register XBR0. See

Section "12. Port Input/Output" on

page 95

for details on Port I/O configuration.

Page 36

DS004-2.2 APR 03

PRELIMINARY

C8051F300/2

5.3.2.

Tracking Modes

The AD0TM bit in register ADC0CN controls the ADC0 track-and-hold mode. In its default state, the ADC0 input is
continuously tracked except when a conversion is in progress. When the AD0TM bit is logic 1, ADC0 operates in
low-power track-and-hold mode. In this mode, each conversion is preceded by a tracking period of 3 SAR clocks
(after the start-of-conversion signal). When the CNVSTR signal is used to initiate conversions in low-power tracking
mode, ADC0 tracks only when CNVSTR is low; conversion begins on the rising edge of CNVSTR (see Figure 5.4).
Tracking can also be disabled (shutdown) when the device is in low power standby or sleep modes. Low-power track-
and-hold mode is also useful when AMUX or PGA settings are frequently changed, due to the settling time require-
ments described in

Section "5.3.3. Settling Time Requirements" on page 37

Figure 5.4. 8-Bit ADC Track and Conversion Example Timing

Write '1' to AD0BUSY,

Timer 0, Timer 2, Timer 1 Overflow

(AD0CM[2:0]=000, 001, 010, 011)

AD0TM=1

Track

Convert

Low Power Mode

AD0TM=0

Track or

Convert

Track

Low Power

or Convert

SAR Clocks

10 11 12

SAR Clocks

B. ADC Timing for Internal Trigger Source

CNVSTR

(AD0CM[2:0]=1xx)

AD0TM=1

A. ADC Timing for External Trigger Source

SAR Clocks

Track or Convert

Convert

Track

AD0TM=0

Track

Convert

Low Power Mode

Low Power

or Convert

DS004-2.2 APR 03

Page 37

PRELIMINARY

C8051F300/2

5.3.3.

Settling Time Requirements

When the ADC0 input configuration is changed (i.e., a different AMUX0 or PGA selection is made), a minimum
tracking time is required before an accurate conversion can be performed. This tracking time is determined by the
AMUX0 resistance, the ADC0 sampling capacitance, any external source resistance, and the accuracy required for
the conversion. Note that in low-power tracking mode, three SAR clocks are used for tracking at the start of every
conversion. For most applications, these three SAR clocks will meet the minimum tracking time requirements.

Figure 5.5 shows the equivalent ADC0 input circuits for both Differential and Single-ended modes. Notice that the
equivalent time constant for both input circuits is the same. The required ADC0 settling time for a given settling
accuracy (SA) may be approximated by Equation 5.1. When measuring the Temperature Sensor output or VDD with
respect to GND, R

TOTAL

reduces to R

MUX

. See Table 5.1 for ADC0 minimum settling time (track/hold time) require-

ments.

Where:
SA is the settling accuracy, given as a fraction of an LSB (for example, 0.25 to settle within 1/4 LSB)
t is the required settling time in seconds
R

TOTAL

is the sum of the AMUX0 resistance and any external source resistance.

n is the ADC resolution in bits (8).

Equation 5.1. ADC0 Settling Time Requirements

-------

TOTAL

SAMPLE

MUX

= 5k

Input

= R

MUX

* C

SAMPLE

MUX

= 5k

SAMPLE

= 5pF

SAMPLE

= 5pF

MUX Select

Differential Mode

P0.x

P0.y

MUX

= 5k

SAMPLE

= 5pF

Input

= R

MUX

* C

SAMPLE

MUX Select

Single-Ended Mode

P0.x

Note: When the PGA gain is set to 0.5, C

SAMPLE

= 3pF

Figure 5.5. ADC0 Equivalent Input Circuits

DS004-2.2 APR 03

Page 39

PRELIMINARY

C8051F300/2

Figure 5.7. ADC0CF: ADC0 Configuration Register (C8051F300/2)

Bits7-3:

AD0SC4-0: ADC0 SAR Conversion Clock Period Bits.
SAR Conversion clock is derived from system clock by the following equation, where AD0SC refers
to the 5-bit value held in bits AD0SC4-0. SAR Conversion clock requirements are given in Table 5.1.

Bit2:

UNUSED. Read = 0b; Write = don't care.

Bits1-0:

AMP0GN1-0: ADC0 Internal Amplifier Gain (PGA).
00: Gain = 0.5
01: Gain = 1
10: Gain = 2
11: Gain = 4

R/W

Reset Value

AD0SC4

AD0SC3

AD0SC2

AD0SC1

AD0SC0

AMP0GN1 AMP0GN0 11111000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xBC

AD0SC

SYSCLK

CLK

SAR

----------------------

Figure 5.8. ADC0: ADC0 Data Word Register (C8051F300/2)

Bits7-0:

ADC0 Data Word.
ADC0 holds the output data byte from the last ADC0 conversion. When in Single-ended mode,
ADC0 holds an 8-bit unsigned integer. When in Differential mode, ADC0 holds a 2's complement
signed 8-bit integer.

R/W

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xBE

Page 40

DS004-2.2 APR 03

PRELIMINARY

C8051F300/2

Figure 5.9. ADC0CN: ADC0 Control Register (C8051F300/2)

Bit7:

AD0EN: ADC0 Enable Bit.
0: ADC0 Disabled. ADC0 is in low-power shutdown.
1: ADC0 Enabled. ADC0 is active and ready for data conversions.

Bit6:

AD0TM: ADC0 Track Mode Bit.
0: Normal Track Mode: When ADC0 is enabled, tracking is continuous unless a conversion is in
progress.
1: Low-power Track Mode: Tracking Defined by AD0CM2-0 bits (see below).

Bit5:

AD0INT: ADC0 Conversion Complete Interrupt Flag.
0: ADC0 has not completed a data conversion since the last time AD0INT was cleared.
1: ADC0 has completed a data conversion.

Bit4:

AD0BUSY: ADC0 Busy Bit.
Read: Unused.
Write:
0: No Effect.
1: Initiates ADC0 Conversion if AD0CM2-0 = 000b

Bit3:

AD0WINT: ADC0 Window Compare Interrupt Flag.
0: ADC0 Window Comparison Data match has not occurred since this flag was last cleared.
1: ADC0 Window Comparison Data match has occurred.

Bits2-0:

AD0CM2-0: ADC0 Start of Conversion Mode Select.
When AD0TM = 0:
000: ADC0 conversion initiated on every write of `1' to AD0BUSY.
001: ADC0 conversion initiated on overflow of Timer 0.
010: ADC0 conversion initiated on overflow of Timer 2.
011: ADC0 conversion initiated on overflow of Timer 1.
1xx: ADC0 conversion initiated on rising edge of external CNVSTR.
When AD0TM = 1:
000: Tracking initiated on write of `1' to AD0BUSY and lasts 3 SAR clocks, followed by conversion.
001: Tracking initiated on overflow of Timer 0 and lasts 3 SAR clocks, followed by conversion.
010: Tracking initiated on overflow of Timer 2 and lasts 3 SAR clocks, followed by conversion.
011: Tracking initiated on overflow of Timer 1 and lasts 3 SAR clocks, followed by conversion.
1xx: ADC0 tracks only when CNVSTR input is logic low; conversion starts on rising CNVSTR
edge.

R/W

Reset Value

AD0EN

AD0TM

AD0INT AD0BUSY AD0WINT AD0CM2

AD0CM1

AD0CM0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

(bit addressable)

0xE8

DS004-2.2 APR 03

Page 41

PRELIMINARY

C8051F300/2

5.4.

Programmable Window Detector

The ADC Programmable Window Detector continuously compares the ADC0 output to user-programmed limits, and
notifies the system when a desired condition is detected. This is especially effective in an interrupt-driven system,
saving code space and CPU bandwidth while delivering faster system response times. The window detector interrupt
flag (AD0WINT in register ADC0CN) can also be used in polled mode. The ADC0 Greater-Than (ADC0GT) and
Less-Than (ADC0LT) registers hold the comparison values. Example comparisons for Single-ended and Differential
modes are shown in Figure 5.10 and Figure 5.11, respectively. Notice that the window detector flag can be pro-
grammed to indicate when measured data is inside or outside of the user-programmed limits depending on the con-
tents of the ADC0LT and ADC0GT registers.

5.4.1.

Window Detector In Single-Ended Mode

Figure 5.10 shows two example window comparisons for Single-ended mode, with ADC0LT = 0x20 and
ADC0GT = 0x10. Notice that in Single-ended mode, the codes vary from 0 to VREF*(255/256) and are represented
as 8-bit unsigned integers. In the left example, an AD0WINT interrupt will be generated if the ADC0 conversion
word (ADC0) is within the range defined by ADC0GT and ADC0LT (if 0x10

< ADC0 < 0x20). In the right example,

and AD0WINT interrupt will be generated if ADC0 is outside of the range defined by ADC0GT and ADC0LT
(if ADC0

< 0x10 or ADC0 > 0x20).

Figure 5.10. ADC Window Compare Examples, Single-Ended Mode

0xFF

0x21

0x20

0x1F

0x11

0x10

0x0F

0x00

Input Voltage
(P0.x - GND)

REF x (255/256)

REF x (32/256)

REF x (16/256)

AD0WINT=1

AD0WINT

not affected

AD0WINT

not affected

ADC0LT

ADC0GT

0xFF

0x21

0x20

0x1F

0x11

0x10

0x0F

0x00

Input Voltage
(P0.x - GND)

REF x (255/256)

REF x (32/256)

REF x (16/256)

AD0WINT

not affected

ADC0GT

ADC0LT

AD0WINT=1

ADC0

Page 42

DS004-2.2 APR 03

PRELIMINARY

C8051F300/2

5.4.2.

Window Detector In Differential Mode

Figure 5.11 shows two example window comparisons for differential mode, with ADC0LT = 0x10 (+16d) and
ADC0GT = 0xFF (-1d). Notice that in Differential mode, the codes vary from -VREF to VREF*(127/128) and are
represented as 8-bit 2's complement signed integers. In the left example, an AD0WINT interrupt will be generated if
the ADC0 conversion word (ADC0L) is within the range defined by ADC0GT and ADC0LT (if 0xFF (-1d) < ADC0
< 0x10 (16d)). In the right example, an AD0WINT interrupt will be generated if ADC0 is outside of the range defined
by ADC0GT and ADC0LT (if ADC0 < 0xFF (-1d) or ADC0 > 0x10 (+16d)).

Figure 5.11. ADC Window Compare Examples, Differential Mode

0x7F (127d)

0x11 (17d)

0x10 (16d)

0x0F (15d)

0x00 (0d)

0xFF (-1d)

0xFE (-2d)

0x80 (-128d)

-REF

Input Voltage

(P0.x - P0.y)

REF x (127/128)

REF x (16/128)

REF x (-1/256)

0x7F (127d)

0x11 (17d)

0x10 (16d)

0x0F (15d)

0x00 (0d)

0xFF (-1d)

0xFE (-2d)

0x80 (-128d)

-REF

Input Voltage

(P0.x - P0.y)

REF x (127/128)

REF x (16/128)

REF x (-1/256)

AD0WINT=1

AD0WINT

not affected

AD0WINT

not affected

ADC0LT

ADC0GT

AD0WINT

not affected

ADC0GT

ADC0LT

AD0WINT=1

ADC0

Page 44

DS004-2.2 APR 03

PRELIMINARY

C8051F300/2

Table 5.1. ADC0 Electrical Characteristics

VDD = 3.0 V, VREF = 2.40 V (REFSL=0), PGA Gain = 1, -40°C to +85°C unless otherwise specified

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

DC ACCURACY

Resolution

bits

Integral Nonlinearity

±0.5

±1

LSB

Differential Nonlinearity

Guaranteed Monotonic

±0.5

±1

LSB

Offset Error

Note 1

0.5±0.6

LSB

Full Scale Error

Differential mode; See Note 1

-1±0.5

LSB

Offset Temperature Coefficient

TBD

ppm/°C

DYNAMIC PERFORMANCE (10 kHz sine-wave Differential input, 1 dB below Full Scale, 500 ksps)

Signal-to-Noise Plus Distortion

Total Harmonic Distortion

Up to the 5

harmonic

-56

Spurious-Free Dynamic Range

CONVERSION RATE

SAR Conversion Clock

MHz

Conversion Time in SAR Clocks

clocks

Track/Hold Acquisition Time

300

Throughput Rate

500

ksps

ANALOG INPUTS

Input Voltage Range

VREF

Input Capacitance

TEMPERATURE SENSOR

Linearity

Notes 1, 2, 3

±0.5

°C

Gain

Notes 1, 2, 3

3350
±110

µV / °C

Offset

Notes 1, 2, 3 (Temp = 0 °C)

897±31

POWER SPECIFICATIONS

Power Supply Current (VDD sup-
plied to ADC0)

Operating Mode, 500 ksps

400

900

µA

Power Supply Rejection

±0.3

mV/V

Note 1: Represents one standard deviation from the mean.
Note 2: Measured with PGA Gain = 2.
Note 3: Includes ADC offset, gain, and linearity variations.

DS004-2.2 APR 03

Page 45

PRELIMINARY

C8051F300/2

VOLTAGE REFERENCE (C8051F300/2)

The voltage reference MUX on C8051F300/2 devices is configurable to use an externally connected voltage refer-
ence or the power supply voltage, VDD (see Figure 6.1). The REFSL bit in the Reference Control register (REF0CN)
selects the reference source. For an external source, REFSL should be set to `0'; For VDD as the reference source,
REFSL should be set to `1'.

The BIASE bit enables the internal voltage bias generator, which is used by the ADC, Temperature Sensor, and Inter-
nal Oscillator. This bit is forced to logic 1 when any of the aforementioned peripherals is enabled. The bias generator
may be enabled manually by writing a `1' to the BIASE bit in register REF0CN; see Figure 6.2 for REF0CN register
details. The electrical specifications for the voltage reference circuit are given in Table 6.1.

Important Note About the VREF Input: Port pin P0.0 is used as the external VREF input. When using an external
voltage reference, P0.0 should be configured as analog input and skipped by the Digital Crossbar. To configure P0.0
as analog input, set to `1' Bit0 in register P0MDIN. To configure the Crossbar to skip P0.0, set to `1' Bit0 in register
XBR0. Refer to

Section "12. Port Input/Output" on page 95

for complete Port I/O configuration details. The exter-

nal reference voltage must be within the range 0

VREF VDD.

On C8051F300/2 devices, the temperature sensor connects to the highest order input of the ADC0 positive input mul-
tiplexer (see

Section "5.1. Analog Multiplexer and PGA" on page 32

for details). The TEMPE bit in register

REF0CN enables/disables the temperature sensor. While disabled, the temperature sensor defaults to a high imped-
ance state and any ADC0 measurements performed on the sensor result in meaningless data.

Figure 6.1. Voltage Reference Functional Block Diagram

Internal
VREF
(to ADC)

To Analog Mux

VDD

VREF

VDD

External

Voltage

Reference

Circuit

GND

REF0CN

BIASE

Temp Sensor

Bias Generator

To ADC, Internal
Oscillator,
Temperature Sensor

IOSCEN

DS004-2.2 APR 03

Page 47

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

COMPARATOR0

C8051F300/1/2/3/4/5 devices include an on-chip programmable voltage comparator, which is shown in Figure 7.1.
Comparator0 offers programmable response time and hysteresis, an analog input multiplexer, and two outputs that are
optionally available at the Port pins: a synchronous "latched" output (CP0), or an asynchronous "raw" output
(CP0A). The asynchronous CP0A signal is available even when the system clock is not active. This allows
Comparator0 to operate and generate an output with the device in STOP mode. When assigned to a Port pin, the
Comparator0 output may be configured as open drain or push-pull (see

Section "12.2. Port I/O Initialization" on

page 98

). Comparator0 may also be used as a reset source (see

Section "9.5. Comparator0 Reset" on page 79

The inputs for Comparator0 are selected in the CPT0MX register (Figure 7.4). The CMX0P1-CMX0P0 bits select the
Comparator0 positive input; the CMX0N1-CMX0N0 bits select the Comparator0 negative input.

Important Note About Comparator Inputs: The Port pins selected as comparator inputs should be configured as
analog inputs in their associated Port configuration register, and configured to be skipped by the Crossbar (for details
on Port configuration, see

Section "12.3. General Purpose Port I/O" on page 101

VDD

CPT

Reset

Decision

Tree

Crossbar

Interrupt

Logic

SET

CLR

SET

CLR

(SYNCHRONIZER)

GND

CP0 +

P0.0

P0.2

P0.4

P0.6

CP0 -

P0.1

P0.3

P0.5

P0.7

CP0EN

CP0OUT

CP0RIF

CP0FIF

CP0HYP1

CP0HYP0

CP0HYN1

CP0HYN0

CMX0N1

CMX0N0

CMX0P1

CMX0P0

T0MD

CP0MD1

CP0MD0

CP0

Rising-edge

Interrupt Flag

CP0

Falling-edge

Interrupt Flag

CP0

CP0A

Figure 7.1. Comparator0 Functional Block Diagram

Page 48

DS004-2.2 APR 03

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

The output of Comparator0 can be polled in software, used as an interrupt source, and/or routed to a Port pin. When
routed to a Port pin, the Comparator0 output is available asynchronous or synchronous to the system clock; the asyn-
chronous output is available even in STOP mode (with no system clock active). When disabled, the Comparator0 out-
put (if assigned to a Port I/O pin via the Crossbar) defaults to the logic low state, and its supply current falls to less
than 100 nA. See

Section "12.1. Priority Crossbar Decoder" on page 96

for details on configuring the

Comparator0 output via the digital Crossbar. Comparator0 inputs can be externally driven from -0.25 V to
(VDD) + 0.25 V without damage or upset. The complete electrical specifications for Comparator0 are given in
Table 7.1.

The Comparator0 response time may be configured in software via the CP0MD1-0 bits in register CPT0MD (see
Figure 7.5). Selecting a longer response time reduces the amount of power consumed by Comparator0. See Table 7.1
for complete timing and power consumption specifications.

The hysteresis of Comparator0 is software-programmable via its Comparator0 Control register (CPT0CN). The user
can program both the amount of hysteresis voltage (referred to the input voltage) and the positive and negative-going
symmetry of this hysteresis around the threshold voltage.

The Comparator0 hysteresis is programmed using Bits3-0 in the Comparator0 Control Register CPT0CN (shown in
Figure 7.3). The amount of negative hysteresis voltage is determined by the settings of the CP0HYN bits. As shown
in Figure 7.2, settings of 20, 10 or 5 mV of negative hysteresis can be programmed, or negative hysteresis can be dis-
abled. In a similar way, the amount of positive hysteresis is determined by the setting the CP0HYP bits.

Positive Hysteresis Voltage

(Programmed with CP0HYP Bits)

Negative Hysteresis Voltage

(Programmed by CP0HYN Bits)

VIN-

VIN+

INPUTS

CIRCUIT CONFIGURATION

CP0+

CP0-

CP0

VIN+

VIN-

OUT

Positive Hysteresis

Disabled

Maximum

Positive Hysteresis

Negative Hysteresis

Disabled

Maximum

Negative Hysteresis

OUTPUT

Figure 7.2. Comparator Hysteresis Plot

DS004-2.2 APR 03

Page 49

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

Comparator0 interrupts can be generated on both rising-edge and falling-edge output transitions. (For Interrupt
enable and priority control, see

Section "8.3. Interrupt Handler" on page 67

). The CP0FIF flag is set to logic 1

upon a Comparator0 falling-edge interrupt, and the CP0RIF flag is set to logic 1 upon the Comparator0 rising-edge
interrupt. Once set, these bits remain set until cleared by software. The output state of Comparator0 can be obtained at
any time by reading the CP0OUT bit. Comparator0 is enabled by setting the CP0EN bit to logic 1, and is disabled by
clearing this bit to logic 0.

Figure 7.3. CPT0CN: Comparator0 Control Register

Bit7:

CP0EN: Comparator0 Enable Bit.
0: Comparator0 Disabled.
1: Comparator0 Enabled.

Bit6:

CP0OUT: Comparator0 Output State Flag.
0: Voltage on CP0+ < CP0-.
1: Voltage on CP0+ > CP0-.

Bit5:

CP0RIF: Comparator0 Rising-Edge Interrupt Flag.
0: No Comparator0 Rising Edge Interrupt has occurred since this flag was last cleared.
1: Comparator0 Rising Edge Interrupt has occurred.

Bit4:

CP0FIF: Comparator0 Falling-Edge Interrupt Flag.
0: No Comparator0 Falling-Edge Interrupt has occurred since this flag was last cleared.
1: Comparator0 Falling-Edge Interrupt has occurred.

Bits3-2:

CP0HYP1-0: Comparator0 Positive Hysteresis Control Bits.
00: Positive Hysteresis Disabled.
01: Positive Hysteresis = 5 mV.
10: Positive Hysteresis = 10 mV.
11: Positive Hysteresis = 20 mV.

Bits1-0:

CP0HYN1-0: Comparator0 Negative Hysteresis Control Bits.
00: Negative Hysteresis Disabled.
01: Negative Hysteresis = 5 mV.
10: Negative Hysteresis = 10 mV.
11: Negative Hysteresis = 20 mV.

R/W

Reset Value

CP0EN

CP0OUT

CP0RIF

CP0FIF

CP0HYP1 CP0HYP0 CP0HYN1 CP0HYN0 00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xF8

Page 52

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PRELIMINARY

C8051F300/1/2/3

C8051F304/5

Table 7.1. Comparator0 Electrical Characteristics

VDD = 3.0 V, -40°C to +85°C unless otherwise specified.

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Response Time:

Mode 0, Vcm

= 1.5 V

CP0+ - CP0- = 100 mV

100

CP0+ - CP0- = -100 mV

250

Response Time:

Mode 1, Vcm

= 1.5 V

CP0+ - CP0- = 100 mV

175

CP0+ - CP0- = -100 mV

500

Response Time:

Mode 2, Vcm

= 1.5 V

CP0+ - CP0- = 100 mV

320

CP0+ - CP0- = -100 mV

1100

Response Time:

Mode 3, Vcm

= 1.5 V

CP0+ - CP0- = 100 mV

1050

CP0+ - CP0- = -100 mV

5200

Common-Mode Rejection Ratio

1.5

mV/V

Positive Hysteresis 1

CP0HYP1-0 = 00

Positive Hysteresis 2

CP0HYP1-0 = 01

Positive Hysteresis 3

CP0HYP1-0 = 10

Positive Hysteresis 4

CP0HYP1-0 = 11

Negative Hysteresis 1

CP0HYN1-0 = 00

Negative Hysteresis 2

CP0HYN1-0 = 01

Negative Hysteresis 3

CP0HYN1-0 = 10

Negative Hysteresis 4

CP0HYN1-0 = 11

Inverting or Non-Inverting Input
Voltage Range

-0.25

VDD +

0.25

Input Capacitance

Input Bias Current

-5

0.001

Input Offset Voltage

-5

POWER SUPPLY

Power Supply Rejection

0.1

mV/V

Power-up Time

µs

Supply Current at DC

Mode 0

7.6

µA

Mode 1

3.2

µA

Mode 2

1.3

µA

Mode 3

0.4

µA

Vcm is the common-mode voltage on CP0+ and CP0-.

DS004-2.2 APR 03

Page 53

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

CIP-51 MICROCONTROLLER

The MCU system controller core is the CIP-51 microcontroller. The CIP-51 is fully compatible with the MCS-51TM
instruction set; standard 803x/805x assemblers and compilers can be used to develop software. The MCU family has
a superset of all the peripherals included with a standard 8051. Included are three 16-bit counter/timers (see descrip-
tion in

Section 15

), an enhanced full-duplex UART (see description in

Section 14

), 256 bytes of internal RAM,

128 byte Special Function Register (SFR) address space (

Section 8.2.6

), and one byte-wide I/O Port (see description

Section 12

). The CIP-51 also includes on-chip debug hardware (see description in

Section 17

), and interfaces

directly with the analog and digital subsystems providing a complete data acquisition or control-system solution in a
single integrated circuit.

The CIP-51 Microcontroller core implements the standard 8051 organization and peripherals as well as additional
custom peripherals and functions to extend its capability (see Figure 8.1 for a block diagram). The CIP-51 includes
the following features:

Fully Compatible with MCS-51 Instruction Set

Extended Interrupt Handler

25 MIPS Peak Throughput with 25 MHz Clock

Reset Input

0 to 25 MHz Clock Frequency

Power Management Modes

256 Bytes of Internal RAM

On-chip Debug Logic

Byte-Wide I/O Port

Program and Data Memory Security

DATA BUS

TMP1

TMP2

PRGM. ADDRESS REG.

PC INCREMENTER

ALU

PSW

DATA BUS

MEMORY

INTERFACE

MEM_ADDRESS

PIPELINE

BUFFER

DATA POINTER

INTERRUPT
INTERFACE

SYSTEM_IRQs

EMULATION_IRQ

MEM_CONTROL

CONTROL

LOGIC

A16

PROGRAM COUNTER (PC)

STOP

CLOCK

RESET

IDLE

POWER CONTROL

SFR
BUS

INTERFACE

SFR_ADDRESS

SFR_CONTROL

SFR_WRITE_DATA

SFR_READ_DATA

B REGISTER

ACCUMULATOR

MEM_WRITE_DATA

MEM_READ_DATA

SRAM

ADDRESS

SRAM

(256 X 8)

STACK POINTER

Figure 8.1. CIP-51 Block Diagram

Page 54

DS004-2.2 APR 03

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

Performance
The CIP-51 employs a pipelined architecture that greatly increases its instruction throughput over the standard 8051
architecture. In a standard 8051, all instructions except for MUL and DIV take 12 or 24 system clock cycles to exe-
cute, and usually have a maximum system clock of 12 MHz. By contrast, the CIP-51 core executes 70% of its instruc-
tions in one or two system clock cycles, with no instructions taking more than eight system clock cycles.

With the CIP-51's maximum system clock at 25 MHz, it has a peak throughput of 25 MIPS. The CIP-51 has a total of
109 instructions. The table below shows the total number of instrutions that require each execution time.

Programming and Debugging Support
In-system programming of the FLASH program memory and communication with on-chip debug support logic is
accomplished via the Cygnal 2-Wire Development Interface (C2). Note that the re-programmable FLASH can also be
read and changed a single byte at a time by the application software using the MOVC and MOVX instructions. This
feature allows program memory to be used for non-volatile data storage as well as updating program code under soft-
ware control.

The on-chip debug support logic facilitates full speed in-circuit debugging, allowing the setting of hardware break-
points, starting, stopping and single stepping through program execution (including interrupt service routines), exam-
ination of the program's call stack, and reading/writing the contents of registers and memory. This method of on-chip
debugging is completely non-intrusive, requiring no RAM, Stack, timers, or other on-chip resources. C2 details can
be found in

Section "17. C2 Interface" on page 161

The CIP-51 is supported by development tools from Cygnal Integrated Products and third party vendors. Cygnal pro-
vides an integrated development environment (IDE) including editor, macro assembler, debugger and programmer.
The IDE's debugger and programmer interface to the CIP-51 via the C2 interface to provide fast and efficient in-sys-
tem device programming and debugging. Third party macro assemblers and C compilers are also available.

Clocks to Execute

2/3

3/4

4/5

Number of Instructions

DS004-2.2 APR 03

Page 55

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

8.1.

INSTRUCTION SET

The instruction set of the CIP-51 System Controller is fully compatible with the standard MCS-51TM instruction set.
Standard 8051 development tools can be used to develop software for the CIP-51. All CIP-51 instructions are the
binary and functional equivalent of their MCS-51TM counterparts, including opcodes, addressing modes and effect on
PSW flags. However, instruction timing is different than that of the standard 8051.

8.1.1.

Instruction and CPU Timing

In many 8051 implementations, a distinction is made between machine cycles and clock cycles, with machine cycles
varying from 2 to 12 clock cycles in length. However, the CIP-51 implementation is based solely on clock cycle tim-
ing. All instruction timings are specified in terms of clock cycles.

Due to the pipelined architecture of the CIP-51, most instructions execute in the same number of clock cycles as there
are program bytes in the instruction. Conditional branch instructions take one less clock cycle to complete when the
branch is not taken as opposed to when the branch is taken. Table 8.1 is the CIP-51 Instruction Set Summary,
which includes the mnemonic, number of bytes, and number of clock cycles for each instruction.

8.1.2.

MOVX Instruction and Program Memory

The MOVX instruction is typically used to access external data memory (Note: the C8051F300/1/2/3/4/5 does not
support external data or program memory). In the CIP-51, the MOVX instruction accesses the on-chip program mem-
ory space implemented as re-programmable FLASH memory. This feature provides a mechanism for the CIP-51 to
update program code and use the program memory space for non-volatile data storage. Refer to

Section "10. FLASH

Memory" on page 83

for further details.

Table 8.1. CIP-51 Instruction Set Summary

Mnemonic

Description

Bytes

Clock

Cycles

ARITHMETIC OPERATIONS

ADD A, Rn

Add register to A

ADD A, direct

Add direct byte to A

ADD A, @Ri

Add indirect RAM to A

ADD A, #data

Add immediate to A

ADDC A, Rn

Add register to A with carry

ADDC A, direct

Add direct byte to A with carry

ADDC A, @Ri

Add indirect RAM to A with carry

ADDC A, #data

Add immediate to A with carry

SUBB A, Rn

Subtract register from A with borrow

SUBB A, direct

Subtract direct byte from A with borrow

SUBB A, @Ri

Subtract indirect RAM from A with borrow

SUBB A, #data

Subtract immediate from A with borrow

INC A

Increment A

INC Rn

Increment register

INC direct

Increment direct byte

INC @Ri

Increment indirect RAM

DEC A

Decrement A

DEC Rn

Decrement register

DEC direct

Decrement direct byte

DEC @Ri

Decrement indirect RAM

INC DPTR

Increment Data Pointer

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PRELIMINARY

C8051F300/1/2/3

C8051F304/5

MUL AB

Multiply A and B

DIV AB

Divide A by B

DA A

Decimal adjust A

LOGICAL OPERATIONS

ANL A, Rn

AND Register to A

ANL A, direct

AND direct byte to A

ANL A, @Ri

AND indirect RAM to A

ANL A, #data

AND immediate to A

ANL direct, A

AND A to direct byte

ANL direct, #data

AND immediate to direct byte

ORL A, Rn

OR Register to A

ORL A, direct

OR direct byte to A

ORL A, @Ri

OR indirect RAM to A

ORL A, #data

OR immediate to A

ORL direct, A

OR A to direct byte

ORL direct, #data

OR immediate to direct byte

XRL A, Rn

Exclusive-OR Register to A

XRL A, direct

Exclusive-OR direct byte to A

XRL A, @Ri

Exclusive-OR indirect RAM to A

XRL A, #data

Exclusive-OR immediate to A

XRL direct, A

Exclusive-OR A to direct byte

XRL direct, #data

Exclusive-OR immediate to direct byte

CLR A

Clear A

CPL A

Complement A

RL A

Rotate A left

RLC A

Rotate A left through Carry

RR A

Rotate A right

RRC A

Rotate A right through Carry

SWAP A

Swap nibbles of A

DATA TRANSFER

MOV A, Rn

Move Register to A

MOV A, direct

Move direct byte to A

MOV A, @Ri

Move indirect RAM to A

MOV A, #data

Move immediate to A

MOV Rn, A

Move A to Register

MOV Rn, direct

Move direct byte to Register

MOV Rn, #data

Move immediate to Register

MOV direct, A

Move A to direct byte

MOV direct, Rn

Move Register to direct byte

MOV direct, direct

Move direct byte to direct byte

MOV direct, @Ri

Move indirect RAM to direct byte

MOV direct, #data

Move immediate to direct byte

MOV @Ri, A

Move A to indirect RAM

MOV @Ri, direct

Move direct byte to indirect RAM

MOV @Ri, #data

Move immediate to indirect RAM

Table 8.1. CIP-51 Instruction Set Summary

Mnemonic

Description

Bytes

Clock

Cycles

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MOV DPTR, #data16

Load DPTR with 16-bit constant

MOVC A, @A+DPTR

Move code byte relative DPTR to A

MOVC A, @A+PC

Move code byte relative PC to A

MOVX A, @Ri

Move external data (8-bit address) to A

MOVX @Ri, A

Move A to external data (8-bit address)

MOVX A, @DPTR

Move external data (16-bit address) to A

MOVX @DPTR, A

Move A to external data (16-bit address)

PUSH direct

Push direct byte onto stack

POP direct

Pop direct byte from stack

XCH A, Rn

Exchange Register with A

XCH A, direct

Exchange direct byte with A

XCH A, @Ri

Exchange indirect RAM with A

XCHD A, @Ri

Exchange low nibble of indirect RAM with A

BOOLEAN MANIPULATION

CLR C

Clear Carry

CLR bit

Clear direct bit

SETB C

Set Carry

SETB bit

Set direct bit

CPL C

Complement Carry

CPL bit

Complement direct bit

ANL C, bit

AND direct bit to Carry

ANL C, /bit

AND complement of direct bit to Carry

ORL C, bit

OR direct bit to carry

ORL C, /bit

OR complement of direct bit to Carry

MOV C, bit

Move direct bit to Carry

MOV bit, C

Move Carry to direct bit

JC rel

Jump if Carry is set

2/3

JNC rel

Jump if Carry is not set

2/3

JB bit, rel

Jump if direct bit is set

3/4

JNB bit, rel

Jump if direct bit is not set

3/4

JBC bit, rel

Jump if direct bit is set and clear bit

3/4

PROGRAM BRANCHING

ACALL addr11

Absolute subroutine call

LCALL addr16

Long subroutine call

RET

Return from subroutine

RETI

Return from interrupt

AJMP addr11

Absolute jump

LJMP addr16

Long jump

SJMP rel

Short jump (relative address)

JMP @A+DPTR

Jump indirect relative to DPTR

JZ rel

Jump if A equals zero

2/3

JNZ rel

Jump if A does not equal zero

2/3

CJNE A, direct, rel

Compare direct byte to A and jump if not equal

3/4

CJNE A, #data, rel

Compare immediate to A and jump if not equal

3/4

CJNE Rn, #data, rel

Compare immediate to Register and jump if not equal

3/4

Table 8.1. CIP-51 Instruction Set Summary

Mnemonic

Description

Bytes

Clock

Cycles

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CJNE @Ri, #data, rel

Compare immediate to indirect and jump if not equal

4/5

DJNZ Rn, rel

Decrement Register and jump if not zero

2/3

DJNZ direct, rel

Decrement direct byte and jump if not zero

3/4

NOP

No operation

Table 8.1. CIP-51 Instruction Set Summary

Mnemonic

Description

Bytes

Clock

Cycles

Notes on Registers, Operands and Addressing Modes:

Rn - Register R0-R7 of the currently selected register bank.

@Ri - Data RAM location addressed indirectly through R0 or R1.

rel - 8-bit, signed (two's complement) offset relative to the first byte of the following instruction. Used by SJMP
and all conditional jumps.

direct - 8-bit internal data location's address. This could be a direct-access Data RAM location (0x00-0x7F) or an
SFR (0x80-0xFF).

#data - 8-bit constant

#data16 - 16-bit constant

bit - Direct-accessed bit in Data RAM or SFR

addr11 - 11-bit destination address used by ACALL and AJMP. The destination must be within the same 2K-byte
page of program memory as the first byte of the following instruction.

addr16 - 16-bit destination address used by LCALL and LJMP. The destination may be anywhere within the 8K-
byte program memory space.

There is one unused opcode (0xA5) that performs the same function as NOP.
All mnemonics copyrighted © Intel Corporation 1980.

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8.2.

MEMORY ORGANIZATION

The memory organization of the CIP-51 System Controller is similar to that of a standard 8051. There are two sepa-
rate memory spaces: program memory and data memory. Program and data memory share the same address space but
are accessed via different instruction types. The CIP-51 memory organization is shown in Figure 8.2 and Figure 8.3.

8.2.1.

Program Memory

The CIP-51 core has a 64k-byte program memory space. The C8051F300/1/2/3 implements 8192 bytes of this pro-
gram memory space as in-system, re-programmable FLASH memory, organized in a contiguous block from
addresses 0x0000 to 0x1FFF. Note: 512 bytes (0x1E00 - 0x1FFF) of this memory are reserved for factory use and are
not available for user program storage. The C8051F304 implements 4096 bytes of re-programmable FLASH program
memory space; the C8051F305 implements 2048 bytes of re-programmable FLASH program memory space.
Figure 8.2 shows the program memory maps for C8051F300/1/2/3/4/5 devices.

Program memory is normally assumed to be read-only. However, the CIP-51 can write to program memory by setting
the Program Store Write Enable bit (PSCTL.0) and using the MOVX instruction. This feature provides a mechanism
for the CIP-51 to update program code and use the program memory space for non-volatile data storage. Refer to

Sec-

tion "10. FLASH Memory" on page 83

for further details.

FLASH

(In-System

Programmable in 512

Byte Sectors)

0x0000

RESERVED

0x1000

0x0FFF

C8051F304

(4k FLASH)

C8051F300/1/2/3

(8k FLASH)

FLASH

(In-System

Programmable in 512

Byte Sectors)

0x0000

RESERVED

0x1E00

0x1DFF

FLASH

(In-System

Programmable in 512

Byte Sectors)

0x0000

RESERVED

0x0800

0x07FF

C8051F305

(2k FLASH)

Figure 8.2. Program Memory Maps

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8.2.2.

Data Memory

The CIP-51 includes 256 bytes of internal RAM mapped into the data memory space from 0x00 through 0xFF. The
lower 128 bytes of data memory are used for general purpose registers and scratch pad memory. Either direct or indi-
rect addressing may be used to access the lower 128 bytes of data memory. Locations 0x00 through 0x1F are addres-
sable as four banks of general purpose registers, each bank consisting of eight byte-wide registers. The next 16 bytes,
locations 0x20 through 0x2F, may either be addressed as bytes or as 128 bit locations accessible with the direct
addressing mode.

The upper 128 bytes of data memory are accessible only by indirect addressing. This region occupies the same
address space as the Special Function Registers (SFR) but is physically separate from the SFR space. The addressing
mode used by an instruction when accessing locations above 0x7F determines whether the CPU accesses the upper
128 bytes of data memory space or the SFRs. Instructions that use direct addressing will access the SFR space.
Instructions using indirect addressing above 0x7F access the upper 128 bytes of data memory. Figure 8.3 illustrates
the data memory organization of the CIP-51.

8.2.3.

General Purpose Registers

The lower 32 bytes of data memory, locations 0x00 through 0x1F, may be addressed as four banks of general-purpose
registers. Each bank consists of eight byte-wide registers designated R0 through R7. Only one of these banks may be
enabled at a time. Two bits in the program status word, RS0 (PSW.3) and RS1 (PSW.4), select the active register bank
(see description of the PSW in Figure 8.7). This allows fast context switching when entering subroutines and inter-
rupt service routines. Indirect addressing modes use registers R0 and R1 as index registers.

8.2.4.

Bit Addressable Locations

In addition to direct access to data memory organized as bytes, the sixteen data memory locations at 0x20 through
0x2F are also accessible as 128 individually addressable bits. Each bit has a bit address from 0x00 to 0x7F. Bit 0 of
the byte at 0x20 has bit address 0x00 while bit 7 of the byte at 0x20 has bit address 0x07. Bit 7 of the byte at 0x2F has
bit address 0x7F. A bit access is distinguished from a full byte access by the type of instruction used (bit source or
destination operands as opposed to a byte source or destination).

Figure 8.3. Data Memory Map

(Direct and Indirect

Addressing)

0x00

0x7F

Upper 128 RAM

(Indirect Addressing

Only)

0x80

0xFF

Special Function

(Direct Addressing Only)

General Purpose

Registers

0x1F

0x20

0x2F

Bit Addressable

Lower 128 RAM
(Direct and Indirect
Addressing)

0x30

INTERNAL DATA ADDRESS SPACE

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The MCS-51TM assembly language allows an alternate notation for bit addressing of the form XX.B where XX is the
byte address and B is the bit position within the byte. For example, the instruction:

MOV

C, 22.3h

moves the Boolean value at 0x13 (bit 3 of the byte at location 0x22) into the Carry flag.

8.2.5.

Stack

A programmer's stack can be located anywhere in the 256-byte data memory. The stack area is designated using the
Stack Pointer (SP, 0x81) SFR. The SP will point to the last location used. The next value pushed on the stack is placed
at SP+1 and then SP is incremented. A reset initializes the stack pointer to location 0x07. Therefore, the first value
pushed on the stack is placed at location 0x08, which is also the first register (R0) of register bank 1. Thus, if more
than one register bank is to be used, the SP should be initialized to a location in the data memory not being used for
data storage. The stack depth can extend up to 256 bytes.

8.2.6.

Special Function Registers

The direct-access data memory locations from 0x80 to 0xFF constitute the special function registers (SFRs). The
SFRs provide control and data exchange with the CIP-51's resources and peripherals. The CIP-51 duplicates the SFRs
found in a typical 8051 implementation as well as implementing additional SFRs used to configure and access the
sub-systems unique to the MCU. This allows the addition of new functionality while retaining compatibility with the
MCS-51TM instruction set. Table 8.2 lists the SFRs implemented in the CIP-51 System Controller.

The SFR registers are accessed anytime the direct addressing mode is used to access memory locations from 0x80 to
0xFF. SFRs with addresses ending in 0x0 or 0x8 (e.g. P0, TCON, SCON0, IE, etc.) are bit-addressable as well as
byte-addressable. All other SFRs are byte-addressable only. Unoccupied addresses in the SFR space are reserved for
future use. Accessing these areas will have an indeterminate effect and should be avoided. Refer to the corresponding
pages of the datasheet, as indicated in Table 8.3, for a detailed description of each register.

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Table 8.3. Special Function Registers

SFRs are listed in alphabetical order. All undefined SFR locations are reserved
Register

Address

Description

Page No.

ACC

0xE0

Accumulator

ADC0CF

0xBC

ADC0 Configuration

ADC0CN

0xE8

ADC0 Control

ADC0GT

0xC4

ADC0 Greater-Than Compare Word

ADC0LT

0xC6

ADC0 Less-Than Compare Word

ADC0

0xBE

ADC0 Data Word

AMX0SL

0xBB

ADC0 Multiplexer Channel Select

0xF0

B Register

CKCON

0x8E

Clock Control

139

CPT0CN

0xF8

Comparator0 Control

CPT0MD

0x9D

Comparator0 Mode Selection

CPT0MX

0x9F

Comparator0 MUX Selection

DPH

0x83

Data Pointer High

DPL

0x82

Data Pointer Low

EIE1

0xE6

Extended Interrupt Enable 1

EIP1

0xF6

External Interrupt Priority 1

Table 8.2. Special Function Register (SFR) Memory Map

CPT0CN

PCA0L

PCA0H

PCA0CPL0 PCA0CPH0

P0MDIN

EIP1

ADC0CN

PCA0CPL1 PCA0CPH1 PCA0CPL2 PCA0CPH2

RSTSRC

ACC

XBR0

XBR1

XBR2

IT01CF

EIE1

PCA0CN

PCA0MD

PCA0CPM0 PCA0CPM1 PCA0CPM2

PSW

REF0CN

TMR2CN

TMR2RLL TMR2RLH

TMR2L

TMR2H

SMB0CN

SMB0CF

SMB0DAT

ADC0GT

ADC0LT

AMX0SL

ADC0CF

ADC0

OSCXCN

OSCICN

OSCICL

FLSCL

FLKEY

P0MDOUT

SCON0

SBUF0

CPT0MD

CPT0MX

TCON

TMOD

TL0

TL1

TH0

TH1

CKCON

PSCTL

DPL

DPH

PCON

0(8)

1(9)

2(A)

3(B)

4(C)

5(D)

6(E)

7(F)

(bit addressable)

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Register

Address

Description

Page

FLKEY

0xB7

FLASH Lock and Key

FLSCL

0xB6

FLASH Scale

0xA8

Interrupt Enable

0xB8

Interrupt Priority

IT01CF

0xE4

INT0/INT1 Configuration Register

OSCICL

0xB3

Internal Oscillator Calibration

OSCICN

0xB2

Internal Oscillator Control

OSCXCN

0xB1

External Oscillator Control

0x80

Port 0 Latch

101

P0MDIN

0xF1

Port 0 Input Mode Configuration

101

P0MDOUT

0xA4

Port 0 Output Mode Configuration

102

PCA0CN

0xD8

PCA Control

156

PCA0MD

0xD9

PCA Mode

157

PCA0CPH0

0xFC

PCA Capture 0 High

160

PCA0CPH1

0xEA

PCA Capture 1 High

160

PCA0CPH2

0xEC

PCA Capture 2 High

160

PCA0CPL0

0xFB

PCA Capture 0 Low

160

PCA0CPL1

0xE9

PCA Capture 1 Low

160

PCA0CPL2

0xEB

PCA Capture 2 Low

160

PCA0CPM0

0xDA

PCA Module 0 Mode Register

158

PCA0CPM1

0xDB

PCA Module 1 Mode Register

158

PCA0CPM2

0xDC

PCA Module 2 Mode Register

158

PCA0H

0xFA

PCA Counter High

159

PCA0L

0xF9

PCA Counter Low

159

PCON

0x87

Power Control

PSCTL

0x8F

Program Store R/W Control

PSW

0xD0

Program Status Word

REF0CN

0xD1

Voltage Reference Control

RSTSRC

0xEF

Reset Source Configuration/Status

SBUF0

0x99

UART 0 Data Buffer

129

SCON0

0x98

UART 0 Control

128

SMB0CF

0xC1

SMBus Configuration

110

SMB0CN

0xC0

SMBus Control

112

SMB0DAT

0xC2

SMBus Data

114

0x81

Stack Pointer

TMR2CN

0xC8

Timer/Counter 2 Control

143

TCON

0x88

Timer/Counter Control

137

TH0

0x8C

Timer/Counter 0 High

140

TH1

0x8D

Timer/Counter 1 High

140

TL0

0x8A

Timer/Counter 0 Low

140

TL1

0x8B

Timer/Counter 1 Low

140

TMOD

0x89

Timer/Counter Mode

138

TMR2RLH

0xCB

Timer/Counter 2 Reload High

144

TMR2RLL

0xCA

Timer/Counter 2 Reload Low

144

TMR2H

0xCD

Timer/Counter 2 High

144

TMR2L

0xCC

Timer/Counter 2 Low

144

Table 8.3. Special Function Registers

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8.2.7.

Register Descriptions

Following are descriptions of SFRs related to the operation of the CIP-51 System Controller. Reserved bits should not
be set to logic l. Future product versions may use these bits to implement new features in which case the reset value
of the bit will be logic 0, selecting the feature's default state. Detailed descriptions of the remaining SFRs are included
in the sections of the datasheet associated with their corresponding system function.

Register

Address

Description

Page

XBR0

0xE1

Port I/O Crossbar Control 0

XBR1

0xE2

Port I/O Crossbar Control 1

XBR2

0xE3

Port I/O Crossbar Control 2

100

0x97, 0xAE, 0xAF, 0xB4,
0xB6, 0xBF, 0xCE, 0xD2,
0xD3, 0xD4, 0xD5, 0xD6,
0xD7, 0xDD, 0xDE, 0xDF,
0xF5

Reserved

Table 8.3. Special Function Registers

Figure 8.4. DPL: Data Pointer Low Byte

Bits7-0:

DPL: Data Pointer Low.
The DPL register is the low byte of the 16-bit DPTR. DPTR is used to access indirectly addressed
FLASH memory.

R/W

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0x82

Figure 8.5. DPH: Data Pointer High Byte

Bits7-0:

DPH: Data Pointer High.
The DPH register is the high byte of the 16-bit DPTR. DPTR is used to access indirectly addressed
FLASH memory.

R/W

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0x83

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Figure 8.6. SP: Stack Pointer

Bits7-0:

SP: Stack Pointer.
The Stack Pointer holds the location of the top of the stack. The stack pointer is incremented before
every PUSH operation. The SP register defaults to 0x07 after reset.

R/W

Reset Value

00000111

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0x81

Figure 8.7. PSW: Program Status Word

Bit7:

CY: Carry Flag.
This bit is set when the last arithmetic operation resulted in a carry (addition) or a borrow (subtrac-
tion). It is cleared to logic 0 by all other arithmetic operations.

Bit6:

AC: Auxiliary Carry Flag
This bit is set when the last arithmetic operation resulted in a carry into (addition) or a borrow from
(subtraction) the high order nibble. It is cleared to logic 0 by all other arithmetic operations.

Bit5:

F0: User Flag 0.
This is a bit-addressable, general purpose flag for use under software control.

Bits4-3:

RS1-RS0: Register Bank Select.
These bits select which register bank is used during register accesses.

Bit2:

OV: Overflow Flag.
This bit is set to logic 1 if the last arithmetic operation resulted in a carry (addition), borrow (subtrac-
tion), or overflow (multiply or divide). It is cleared to logic 0 by all other arithmetic operations.

Bit1:

F1: User Flag 1.
This is a bit-addressable, general purpose flag for use under software control.

Bit0:

PARITY: Parity Flag.
This bit is set to logic 1 if the sum of the eight bits in the accumulator is odd and cleared if the sum is
even.

R/W

Reset Value

RS1

RS0

PARITY

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

(bit addressable)

0xD0

RS1

RS0

Register Bank

Address

0x00 - 0x07

0x08 - 0x0F

0x10 - 0x17

0x18 - 0x1F

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8.3.

Interrupt Handler

The CIP-51 includes an extended interrupt system supporting a total of 12 interrupt sources with two priority levels.
The allocation of interrupt sources between on-chip peripherals and external inputs pins varies according to the spe-
cific version of the device. Each interrupt source has one or more associated interrupt-pending flag(s) located in an
SFR. When a peripheral or external source meets a valid interrupt condition, the associated interrupt-pending flag is
set to logic 1.

If interrupts are enabled for the source, an interrupt request is generated when the interrupt-pending flag is set. As
soon as execution of the current instruction is complete, the CPU generates an LCALL to a predetermined address to
begin execution of an interrupt service routine (ISR). Each ISR must end with an RETI instruction, which returns pro-
gram execution to the next instruction that would have been executed if the interrupt request had not occurred. If
interrupts are not enabled, the interrupt-pending flag is ignored by the hardware and program execution continues as
normal. (The interrupt-pending flag is set to logic 1 regardless of the interrupt's enable/disable state.)

Each interrupt source can be individually enabled or disabled through the use of an associated interrupt enable bit in
an SFR (IE-EIE1). However, interrupts must first be globally enabled by setting the EA bit (IE.7) to logic 1 before the
individual interrupt enables are recognized. Setting the EA bit to logic 0 disables all interrupt sources regardless of
the individual interrupt-enable settings.

Some interrupt-pending flags are automatically cleared by the hardware when the CPU vectors to the ISR. However,
most are not cleared by the hardware and must be cleared by software before returning from the ISR. If an interrupt-
pending flag remains set after the CPU completes the return-from-interrupt (RETI) instruction, a new interrupt
request will be generated immediately and the CPU will re-enter the ISR after the completion of the next instruction.

8.3.1.

MCU Interrupt Sources and Vectors

The MCUs support 12 interrupt sources. Software can simulate an interrupt by setting any interrupt-pending flag to
logic 1. If interrupts are enabled for the flag, an interrupt request will be generated and the CPU will vector to the ISR
address associated with the interrupt-pending flag. MCU interrupt sources, associated vector addresses, priority order
and control bits are summarized in Table 8.4 on page 69. Refer to the datasheet section associated with a particular
on-chip peripheral for information regarding valid interrupt conditions for the peripheral and the behavior of its inter-
rupt-pending flag(s).

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8.3.2.

External Interrupts

The /INT0 and /INT1 external interrupt sources are configurable as active high or low, edge or level sensitive. The
IN0PL (/INT0 Polarity) and IN1PL (/INT1 Polarity) bits in the IT01CF register select active high or active low; the
IT0 and IT1 bits in TCON (

Section "15.1. Timer 0 and Timer 1" on page 133

) select level or edge sensitive. The

table below lists the possible configurations.

/INT0 and /INT1 are assigned to Port pins as defined in the IT01CF register (see Figure 8.14). Note that /INT0 and
/INT0 Port pin assignments are independent of any Crossbar assignments. /INT0 and /INT1 will monitor their
assigned Port pins without disturbing the peripheral that was assigned the Port pin via the Crossbar. To assign a Port
pin only to /INT0 and/or /INT1, configure the Crossbar to skip the selected pin(s). This is accomplished by setting the
associated bit in register XBR0 (see

Section "12.1. Priority Crossbar Decoder" on page 96

for complete details on

configuring the Crossbar).

IE0 (TCON.1) and IE1 (TCON.3) serve as the interrupt-pending flags for the /INT0 and /INT1 external interrupts,
respectively. If an /INT0 or /INT1 external interrupt is configured as edge-sensitive, the corresponding interrupt-
pending flag is automatically cleared by the hardware when the CPU vectors to the ISR. When configured as level
sensitive, the interrupt-pending flag remains logic 1 while the input is active as defined by the corresponding polarity
bit (IN0PL or IN1PL); the flag remains logic 0 while the input is inactive. The external interrupt source must hold the
input active until the interrupt request is recognized. It must then deactivate the interrupt request before execution of
the ISR completes or another interrupt request will be generated.

8.3.3.

Interrupt Priorities

Each interrupt source can be individually programmed to one of two priority levels: low or high. A low priority inter-
rupt service routine can be preempted by a high priority interrupt. A high priority interrupt cannot be preempted. Each
interrupt has an associated interrupt priority bit in an SFR (IP or EIP1) used to configure its priority level. Low prior-
ity is the default. If two interrupts are recognized simultaneously, the interrupt with the higher priority is serviced
first. If both interrupts have the same priority level, a fixed priority order is used to arbitrate, given in Table 8.4.

8.3.4.

Interrupt Latency

Interrupt response time depends on the state of the CPU when the interrupt occurs. Pending interrupts are sampled
and priority decoded each system clock cycle. Therefore, the fastest possible response time is 5 system clock cycles:
1 clock cycle to detect the interrupt and 4 clock cycles to complete the LCALL to the ISR. If an interrupt is pending
when a RETI is executed, a single instruction is executed before an LCALL is made to service the pending interrupt.
Therefore, the maximum response time for an interrupt (when no other interrupt is currently being serviced or the
new interrupt is of greater priority) occurs when the CPU is performing an RETI instruction followed by a DIV as the
next instruction. In this case, the response time is 18 system clock cycles: 1 clock cycle to detect the interrupt, 5 clock
cycles to execute the RETI, 8 clock cycles to complete the DIV instruction and 4 clock cycles to execute the LCALL
to the ISR. If the CPU is executing an ISR for an interrupt with equal or higher priority, the new interrupt will not be
serviced until the current ISR completes, including the RETI and following instruction.

IT0

IN0PL

/INT0 Interrupt

IT1

IN1PL

/INT1 Interrupt

Active low, edge sensitive

Active high, edge sensitive

Active low, level sensitive

Active high, level sensitive

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Table 8.4. Interrupt Summary

Interrupt Source

Interrupt

Vector

Priority

Order

Pending Flag

r
e

s
s
a

l
e

r
e

Enable
Flag

Priority
Control

Reset

0x0000

Top

None

N/A

Always
Enabled

Always
Highest

External Interrupt 0 (/INT0)

0x0003

IE0 (TCON.1)

EX0 (IE.0)

PX0 (IP.0)

Timer 0 Overflow

0x000B

TF0 (TCON.5)

ET0 (IE.1)

PT0 (IP.1)

External Interrupt 1 (/INT1)

0x0013

IE1 (TCON.3)

EX1 (IE.2)

PX1 (IP.2)

Timer 1 Overflow

0x001B

TF1 (TCON.7)

ET1 (IE.3)

PT1 (IP.3)

UART0

0x0023

RI0 (SCON0.0)
TI0 (SCON0.1)

ES0 (IE.4)

PS0 (IP.4)

Timer 2 Overflow

0x002B

TF2H
(TMR2CN.7)
TF2L
(TMR2CN.6)

ET2 (IE.5)

PT2 (IP.5)

SMBus Interface

0x0033

SI (SMB0CN.0)

ESMB0
(EIE1.0)

PSMB0
(EIP1.0)

ADC0 Window Compare

0x003B

AD0WINT
(ADC0CN.3)

EWADC0
(EIE1.1)

PWADC0
(EIP1.1)

ADC0 Conversion Complete

0x0043

AD0INT
(ADC0CN.5)

EADC0C
(EIE1.2)

PADC0C
(EIP1.2)

Programmable Counter Array

0x004B

CF (PCA0CN.7)
CCFn
(PCA0CN.n)

EPCA0
(EIE1.3)

PPCA0
(EIP1.3)

Comparator0 Falling Edge

0x0053

CP0FIF
(CPT0CN.4)

ECP0F
(EIE1.4)

PCP0F
(EIP1.4)

Comparator0 Rising Edge

0x005B

CP0RIF
(CPT0CN.5)

ECP0R
(EIE1.5)

PCP0R
(EIP1.5)

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8.3.5.

Interrupt Register Descriptions

The SFRs used to enable the interrupt sources and set their priority level are described below. Refer to the datasheet
section associated with a particular on-chip peripheral for information regarding valid interrupt conditions for the
peripheral and the behavior of its interrupt-pending flag(s).

Figure 8.10. IE: Interrupt Enable

Bit7:

EA: Enable All Interrupts.
This bit globally enables/disables all interrupts. It overrides the individual interrupt mask settings.
0: Disable all interrupt sources.
1: Enable each interrupt according to its individual mask setting.

Bit6:

IEGF0: General Purpose Flag 0.
This is a general purpose flag for use under software control.

Bit5:

ET2: Enable Timer 2 Interrupt.
This bit sets the masking of the Timer 2 interrupt.
0: Disable Timer 2 interrupt.
1: Enable interrupt requests generated by the TF2L or TF2H flags.

Bit4:

ES0: Enable UART0 Interrupt.
This bit sets the masking of the UART0 interrupt.
0: Disable UART0 interrupt.
1: Enable UART0 interrupt.

Bit3:

ET1: Enable Timer 1 Interrupt.
This bit sets the masking of the Timer 1 interrupt.
0: Disable all Timer 1 interrupt.
1: Enable interrupt requests generated by the TF1 flag.

Bit2:

EX1: Enable External Interrupt 1.
This bit sets the masking of external interrupt 1.
0: Disable external interrupt 1.
1: Enable interrupt requests generated by the /INT1 input.

Bit1:

ET0: Enable Timer 0 Interrupt.
This bit sets the masking of the Timer 0 interrupt.
0: Disable all Timer 0 interrupt.
1: Enable interrupt requests generated by the TF0 flag.

Bit0:

EX0: Enable External Interrupt 0.
This bit sets the masking of external interrupt 0.
0: Disable external interrupt 0.
1: Enable interrupt requests generated by the /INT0 input.

R/W

Reset Value

IEGF0

ET2

ES0

ET1

EX1

ET0

EX0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

(bit addressable)

0xA8

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Figure 8.11. IP: Interrupt Priority

Bits7-6:

UNUSED. Read = 11b, Write = don't care.

Bit5:

PT2: Timer 2 Interrupt Priority Control.
This bit sets the priority of the Timer 2 interrupt.
0: Timer 2 interrupt priority determined by default priority order.
1: Timer 2 interrupts set to high priority level.

Bit4:

PS0: UART0 Interrupt Priority Control.
This bit sets the priority of the UART0 interrupt.
0: UART0 interrupt priority determined by default priority order.
1: UART0 interrupts set to high priority level.

Bit3:

PT1: Timer 1 Interrupt Priority Control.
This bit sets the priority of the Timer 1 interrupt.
0: Timer 1 interrupt priority determined by default priority order.
1: Timer 1 interrupts set to high priority level.

Bit2:

PX1: External Interrupt 1 Priority Control.
This bit sets the priority of the External Interrupt 1 interrupt.
0: External Interrupt 1 priority determined by default priority order.
1: External Interrupt 1 set to high priority level.

Bit1:

PT0: Timer 0 Interrupt Priority Control.
This bit sets the priority of the Timer 0 interrupt.
0: Timer 0 interrupt priority determined by default priority order.
1: Timer 0 interrupt set to high priority level.

Bit0:

PX0: External Interrupt 0 Priority Control.
This bit sets the priority of the External Interrupt 0 interrupt.
0: External Interrupt 0 priority determined by default priority order.
1: External Interrupt 0 set to high priority level.

R/W

Reset Value

PT2

PS0

PT1

PX1

PT0

PX0

11000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

(bit addressable)

0xB8

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Figure 8.12. EIE1: Extended Interrupt Enable 1

Bits7-6:

UNUSED. Read = 00b. Write = don't care.

Bit5:

ECP0R: Enable Comparator0 (CP0) Rising Edge Interrupt.
This bit sets the masking of the CP0 Rising Edge interrupt.
0: Disable CP0 Rising Edge interrupt.
1: Enable interrupt requests generated by the CP0RIF flag.

Bit4:

ECP0F: Enable Comparator0 (CP0) Falling Edge Interrupt.
This bit sets the masking of the CP0 Falling Edge interrupt.
0: Disable CP0 Falling Edge interrupt.
1: Enable interrupt requests generated by the CP0FIF flag .

Bit3:

EPCA0: Enable Programmable Counter Array (PCA0) Interrupt.
This bit sets the masking of the PCA0 interrupts.
0: Disable all PCA0 interrupts.
1: Enable interrupt requests generated by PCA0.

Bit2:

EADC0C: Enable ADC0 Conversion Complete Interrupt.
This bit sets the masking of the ADC0 Conversion Complete interrupt.
0: Disable ADC0 Conversion Complete interrupt.
1: Enable interrupt requests generated by the AD0INT flag.

Bit1:

EWADC0: Enable Window Comparison ADC0 Interrupt.
This bit sets the masking of ADC0 Window Comparison interrupt.
0: Disable ADC0 Window Comparison interrupt.
1: Enable interrupt requests generated by ADC0 Window Compare flag.

Bit0:

ESMB0: Enable SMBus Interrupt.
This bit sets the masking of the SMBus interrupt.
0: Disable all SMBus interrupts.
1: Enable interrupt requests generated by the SI flag.

R/W

Reset Value

ECP0R

ECP0F

EPCA0

EADC0C

EWADC0

ESMB0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xE6

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Figure 8.13. EIP1: Extended Interrupt Priority 1

Bits7-6:

UNUSED. Read = 11b. Write = don't care.

Bit5:

PCP0R: Comparator0 (CP0) Rising Interrupt Priority Control.
This bit sets the priority of the CP0 rising-edge interrupt.
0: CP0 rising interrupt set to low priority level.
1: CP0 rising interrupt set to high priority level.

Bit4:

PCP0F: Comparator0 (CP0) Falling Interrupt Priority Control.
This bit sets the priority of the CP0 falling-edge interrupt.
0: CP0 falling interrupt set to low priority level.
1: CP0 falling interrupt set to high priority level.

Bit3:

PPCA0: Programmable Counter Array (PCA0) Interrupt Priority Control.
This bit sets the priority of the PCA0 interrupt.
0: PCA0 interrupt set to low priority level.
1: PCA0 interrupt set to high priority level.

Bit2:

PADC0C ADC0 Conversion Complete Interrupt Priority Control
This bit sets the priority of the ADC0 Conversion Complete interrupt.
0: ADC0 Conversion Complete interrupt set to low priority level.
1: ADC0 Conversion Complete interrupt set to high priority level.

Bit1:

PWADC0: ADC0 Window Comparator Interrupt Priority Control.
This bit sets the priority of the ADC0 Window interrupt.
0: ADC0 Window interrupt set to low priority level.
1: ADC0 Window interrupt set to high priority level.

Bit0:

PSMB0: SMBus Interrupt Priority Control.
This bit sets the priority of the SMBus interrupt.
0: SMBus interrupt set to low priority level.
1: SMBus interrupt set to high priority level.

R/W

Reset Value

PCP0R

PCP0F

PPCA0

PADC0C

PWADC0

PSMB0

11000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xF6

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Bit7:

IN1PL: /INT1 Polarity
0: /INT1 input is active low.
1: /INT1 input is active high.

Bits6-4:

IN1SL2-0: /INT1 Port Pin Selection Bits
These bits select which Port pin is assigned to /INT1. Note that this pin assignment is independent of
the Crossbar; /INT1 will monitor the assigned Port pin without disturbing the peripheral that has been
assigned the Port pin via the Crossbar. The Crossbar will not assign the Port pin to a peripheral if it is
configured to skip the selected pin (accomplished by setting to `1' the corresponding bit in register
XBR0).

Bit3:

IN0PL: /INT0 Polarity
0: /INT0 interrupt is active low.
1: /INT0 interrupt is active high.

Bits2-0:

INT0SL2-0: /INT0 Port Pin Selection Bits
These bits select which Port pin is assigned to /INT0. Note that this pin assignment is independent of
the Crossbar. /INT0 will monitor the assigned Port pin without disturbing the peripheral that has been
assigned the Port pin via the Crossbar. The Crossbar will not assign the Port pin to a peripheral if it is
configured to skip the selected pin (accomplished by setting to `1' the corresponding bit in register
XBR0).

R/W

Reset Value

IN1PL

IN1SL2

IN1SL1

IN1SL0

IN0PL

IN0SL2

IN0SL1

IN0SL0

00000001

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xE4

Note: Refer to Figure 15.4 for INT0/1 edge- or level-sensitive interrupt selection.

IN1SL2-0

/INT1 Port Pin

000

P0.0

001

P0.1

010

P0.2

011

P0.3

100

P0.4

101

P0.5

110

P0.6

111

P0.7

IN0SL2-0

/INT0 Port Pin

000

P0.0

001

P0.1

010

P0.2

011

P0.3

100

P0.4

101

P0.5

110

P0.6

111

P0.7

Figure 8.14. IT01CF: INT0/INT1 Configuration Register

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8.4.

Power Management Modes

The CIP-51 core has two software programmable power management modes: Idle and Stop. Idle mode halts the CPU
while leaving the peripherals and clocks active. In Stop mode, the CPU is halted, all interrupts and timers (except the
Missing Clock Detector) are inactive, and the system clock is stopped (analog peripherals remain in their selected
states). Since clocks are running in Idle mode, power consumption is dependent upon the system clock frequency and
the number of peripherals left in active mode before entering Idle. Stop mode consumes the least power. Figure 1.15
describes the Power Control Register (PCON) used to control the CIP-51's power management modes.

Although the CIP-51 has Idle and Stop modes built in (as with any standard 8051 architecture), power management
of the entire MCU is better accomplished by enabling/disabling individual peripherals as needed. Each analog periph-
eral can be disabled when not in use and placed in low power mode. Digital peripherals, such as timers or serial
buses, draw little power when they are not in use. Turning off the oscillators lowers power consuption considerably;
however a reset is required to restart the MCU.

8.4.1.

Idle Mode

Setting the Idle Mode Select bit (PCON.0) causes the CIP-51 to halt the CPU and enter Idle mode as soon as the
instruction that sets the bit completes execution. All internal registers and memory maintain their original data. All
analog and digital peripherals can remain active during Idle mode.

Idle mode is terminated when an enabled interrupt is asserted or a reset occurs. The assertion of an enabled interrupt
will cause the Idle Mode Selection bit (PCON.0) to be cleared and the CPU to resume operation. The pending inter-
rupt will be serviced and the next instruction to be executed after the return from interrupt (RETI) will be the instruc-
tion immediately following the one that set the Idle Mode Select bit. If Idle mode is terminated by an internal or
external reset, the CIP-51 performs a normal reset sequence and begins program execution at address 0x0000.

If enabled, the Watchdog Timer (WDT) will eventually cause an internal watchdog reset and thereby terminate the
Idle mode. This feature protects the system from an unintended permanent shutdown in the event of an inadvertent
write to the PCON register. If this behavior is not desired, the WDT may be disabled by software prior to entering the
Idle mode if the WDT was initially configured to allow this operation. This provides the opportunity for additional
power savings, allowing the system to remain in the Idle mode indefinitely, waiting for an external stimulus to wake
up the system. Refer to

Section "16.3. Watchdog Timer Mode" on page 154

for more information on the use and

configuration of the WDT.

8.4.2.

Stop Mode

Setting the Stop Mode Select bit (PCON.1) causes the CIP-51 to enter Stop mode as soon as the instruction that sets
the bit completes execution.

In Stop mode the internal oscillator, CPU, and all digital peripherals are stopped; the

state of the external oscillator circuit is not affected. Each analog peripheral (including the external oscillator circuit)
may be shut down individually prior to entering Stop Mode. Stop mode can only be terminated by an internal or
external reset. On reset, the CIP-51 performs the normal reset sequence and begins program execution at address
0x0000.

If enabled, the Missing Clock Detector will cause an internal reset and thereby terminate the Stop mode. The Missing
Clock Detector should be disabled if the CPU is to be put to in STOP mode for longer than the MCD timeout of
100 µsec.

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RESET SOURCES

Reset circuitry allows the controller to be easily placed in a predefined default condition. On entry to this reset state,
the following occur:

CIP-51 halts program execution

Special Function Registers (SFRs) are initialized to their defined reset values

External Port pins are forced to a known state

Interrupts and timers are disabled.

All SFRs are reset to the predefined values noted in the SFR detailed descriptions. The contents of internal data mem-
ory are unaffected during a reset; any previously stored data is preserved. However, since the stack pointer SFR is
reset, the stack is effectively lost even though the data on the stack is not altered.

The Port I/O latches are reset to 0xFF (all logic ones) in open-drain mode. Weak pull-ups are enabled during and after
the reset. For VDD Monitor and power-on resets, the /RST pin is driven low until the device exits the reset state.

On exit from the reset state, the program counter (PC) is reset, and the system clock defaults to the internal oscillator.
Refer to

Section "11. Oscillators" on page 89

for information on selecting and configuring the system clock source.

The Watchdog Timer is enabled with the system clock divided by 12 as its clock source (

Section "16.3. Watchdog

Timer Mode" on page 154

details the use of the Watchdog Timer). Once the system clock source is stable, program

execution begins at location 0x0000.

PCA

WDT

Missing

Clock

Detector

(one-
shot)

(Software Reset)

System Reset

Reset
Funnel

P0.x

P0.y

SWRSF

Internal

Oscillator

System
Clock

CIP-51

Microcontroller

Core

Extended Interrupt

Handler

Clock Select

Enable

XTAL1

XTAL2

External

Oscillator

Drive

Illegal

FLASH

Operation

+
-

Comparator 0

C0RSEF

/RST

(wired-OR)

Power On

Reset

+
-

VDD

Supply
Monitor

Enable

'0'

Figure 9.1. Reset Sources

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9.1.

Power-On Reset

During power-up, the device is held in a reset state and the /RST pin is driven low until VDD settles above V

RST

. A

delay occurs before the device is released from reset; the delay decreases as the VDD ramp time increases (VDD
ramp time is defined as how fast VDD ramps from 0 V to 2.7 V). Figure 9.2. plots the power-on and VDD monitor
reset timing. The maximum VDD ramp time is 1 ms; slower ramp times may cause the device to be released from
reset before VDD reaches the V

RST

level. For ramp times less than 1 ms, the power-on reset delay (T

PORDelay

) is typ-

ically less than 0.3 ms.

On exit from a power-on reset, the PORSF flag (RSTSRC.1) is set by hardware to logic 1. When PORSF is set, all of
the other reset flags in the RSTSRC Register are indeterminate (PORSF is cleared by all other resets). Since all resets
cause program execution to begin at the same location (0x0000) software can read the PORSF flag to determine if a
power-up was the cause of reset. The content of internal data memory should be assumed to be undefined after a
power-on reset. The VDD monitor is disabled following a power-on reset.

9.2.

Power-Fail Reset / VDD Monitor

When a power-down transition or power irregularity causes VDD to drop below V

RST

, the power supply monitor will

drive the /RST pin low and hold the CIP-51 in a reset state (see Figure 9.2). When VDD returns to a level above
V

RST

, the CIP-51 will be released from the reset state. Note that even though internal data memory contents are not

altered by the power-fail reset, it is impossible to determine if VDD dropped below the level required for data reten-
tion. If the PORSF flag reads `1', the data may no longer be valid. The VDD monitor is disabled after power-on
resets; however its defined state (enabled/disabled) is not altered by any other reset source. For example, if the VDD
monitor is enabled and a software reset is performed, the VDD monitor will still be enabled after the reset. The VDD
monitor is enabled by writing a `1' to the PORSF bit in register RSTSRC. See Figure 9.2 for VDD monitor timing;
note that the reset delay is not incurred after a VDD monitor reset. See Table 9.2 for electrical characteristics of the
VDD monitor.

Power-On

Reset

VDD

Monitor

Reset

/RST

l
t
s

1.0

2.0

Logic HIGH

Logic LOW

PORDelay

2.70
2.55

RST

VDD

Figure 9.2. Power-On and VDD Monitor Reset Timing

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Important Note: Enabling the VDD monitor will immediately generate a system reset. The device will then return
from the reset state with the VDD monitor enabled. Writing a logic `1' to the PORSF flag when the VDD monitor
is enabled does not cause a system reset.

9.3.

External Reset

The external /RST pin provides a means for external circuitry to force the device into a reset state. Asserting an
active-low signal on the /RST pin generates a reset; an external pull-up and/or decoupling of the /RST pin may be
necessary to avoid erroneous noise-induced resets. See Table 9.2 for complete /RST pin specifications. The PINRSF
flag (RSTSRC.0) is set on exit from an external reset.

9.4.

Missing Clock Detector Reset

The Missing Clock Detector (MCD) is a one-shot circuit that is triggered by the system clock. If the system clock
remains high or low for more than 100 µs, the one-shot will time out and generate a reset. After a MCD reset, the
MCDRSF flag (RSTSRC.2) will read `1', signifying the MCD as the reset source; otherwise, this bit reads `0'. Writ-
ing a `1' to the MCDRSF bit enables the Missing Clock Detector; writing a `0' disables it. The state of the /RST pin
is unaffected by this reset.

9.5.

Comparator0 Reset

Comparator0 can be configured as a reset source by writing a `1' to the C0RSEF flag (RSTSRC.5). Comparator0
should be enabled and allowed to settle prior to writing to C0RSEF to prevent any turn-on chatter on the output from
generating an unwanted reset. The Comparator0 reset is active-low: if the non-inverting input voltage (on CP0+) is
less than the inverting input voltage (on CP0-), the device is put into the reset state. After a Comparator0 reset, the
C0RSEF flag (RSTSRC.5) will read `1' signifying Comparator0 as the reset source; otherwise, this bit reads `0'. The
state of the /RST pin is unaffected by this reset.

9.6.

PCA Watchdog Timer Reset

The programmable Watchdog Timer (WDT) function of the Programmable Counter Array (PCA) can be used to pre-
vent software from running out of control during a system malfunction. The PCA WDT function can be enabled or
disabled by software as described in

Section "16.3. Watchdog Timer Mode" on page 154

; the WDT is enabled and

clocked by SYSCLK / 12 following any reset. If a system malfunction prevents user software from updating the
WDT, a reset is generated and the WDTRSF bit (RSTSRC.5) is set to `1'. The state of the /RST pin is unaffected by
this reset.

9.7.

FLASH Error Reset

If a FLASH read/write/erase or program read targets an illegal address, a system reset is generated. This may occur
due to any of the following:

A FLASH write or erase is attempted above user code space. This occurs when PSWE is set to `1' and a MOVX
operation is attempted above the user code space address limit.

A FLASH read is attempted above user code space. This occurs when a MOVC operation is attempted above the
user code space address limit.

A Program read is attempted above user code space. This occurs when user code attempts to branch to an address
above the user code space address limit.

Table 9.1. User Code Space Address Limits

Device

User Code Space Address Limit

C8051F300/1/2/3

0x1DFF

C8051F304

0x0FFF

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The FERROR bit (RSTSRC.6) is set following a FLASH error reset. The state of the /RST pin is unaffected by this
reset.

9.8.

Software Reset

Software may force a reset by writing a `1' to the SWRSF bit (RSTSRC.4). The SWRSF bit will read `1' following a
software forced reset. The state of the /RST pin is unaffected by this reset.

C8051F305

0x07FF

Table 9.2. Reset Electrical Characteristics

-40°C to +85°C unless otherwise specified.

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

/RST Output Low Voltage

= 8.5 mA, VDD = 2.7 V to 3.6 V

0.6

/RST Input High Voltage

0.7 x

VDD

/RST Input Low Voltage

0.3 x

VDD

/RST Input Leakage Current

/RST = 0.0 V

µA

VDD POR Threshold (V

RST

)

2.40

2.55

2.70

Missing Clock Detector Timeout

Time from last system clock rising

edge to reset initiation

100

220

500

µs

Reset Time Delay

Delay between release of any reset

source and code execution at location

0x0000

5.0

µs

Minimum /RST Low Time to

Generate a System Reset

µs

Table 9.1. User Code Space Address Limits

Device

User Code Space Address Limit

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Figure 9.3. RSTSRC: Reset Source Register

(Note: Do not use read-modify-write operations (ORL, ANL) on this register)

Bit7:

UNUSED. Read = 0. Write = don't care.

Bit6:

FERROR: FLASH Error Indicator.
0: Source of last reset was not a FLASH read/write/erase error.
1: Source of last reset was a FLASH read/write/erase error.

Bit5:

C0RSEF: Comparator0 Reset Enable and Flag.
Write
0: Comparator0 is not a reset source.
1: Comparator0 is a reset source (active-low).
Read
0: Source of last reset was not Comparator0.
1: Source of last reset was Comparator0.

Bit4:

SWRSF: Software Reset Force and Flag.
Write
0: No Effect.
1: Forces a system reset.
Read
0: Source of last reset was not a write to the SWRSF bit.
1: Source of last was a write to the SWRSF bit.

Bit3:

WDTRSF: Watchdog Timer Reset Flag.
0: Source of last reset was not a WDT timeout.
1: Source of last reset was a WDT timeout.

Bit2:

MCDRSF: Missing Clock Detector Flag.
Write:
0: Missing Clock Detector disabled.
1: Missing Clock Detector enabled; triggers a reset if a missing clock condition is detected.
Read:
0: Source of last reset was not a Missing Clock Detector timeout.
1: Source of last reset was a Missing Clock Detector timeout.

Bit1:

PORSF: Power-On Reset Force and Flag.
This bit is set anytime a power-on reset occurs. This may be due to a true power-on reset or a VDD
monitor reset. In either case, data memory should be considered indeterminate following the reset.
Writing this bit enables/disables the VDD monitor.
Write:
0: VDD monitor disabled.
1: VDD monitor enabled.
Read:
0: Last reset was not a power-on or VDD monitor reset.
1: Last reset was a power-on or VDD monitor reset; all other reset flags indeterminate.

Bit0:

PINRSF: HW Pin Reset Flag.
0: Source of last reset was not /RST pin.
1: Source of last reset was /RST pin.

R/W

Reset Value

FERROR

C0RSEF

SWRSF

WDTRSF

MCDRSF

PORSF

PINRSF

Variable

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xEF

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10.

FLASH MEMORY

On-chip, re-programmable FLASH memory is included for program code and non-volatile data storage. The FLASH
memory can be programmed in-system, a single byte at a time, through the C2 interface or by software using the
MOVX instruction. Once cleared to logic 0, a FLASH bit must be erased to set it back to logic 1. FLASH bytes would
typically be erased (set to 0xFF) before being reprogrammed. The write and erase operations are automatically timed
by hardware for proper execution; data polling to determine the end of the write/erase operation is not required. Code
execution is stalled during a FLASH write/erase operation. Refer to Table 10.1 for complete FLASH memory electri-
cal characteristics.

10.1.

Programming The FLASH Memory

The simplest means of programming the FLASH memory is through the C2 interface using programming tools pro-
vided by Cygnal or a third party vendor. This is the only means for programming a non-initialized device. For details
on the C2 commands to program FLASH memory, see

Section "17. C2 Interface" on page 161

To ensure the integrity of FLASH contents, it is strongly recommended that the on-chip VDD Monitor be
enabled in any system that includes code that writes and/or erases FLASH memory from software.

10.1.1. FLASH Lock and Key Functions

FLASH writes and erases by user software are protected with a lock and key function; FLASH reads by user software
are unrestricted. The FLASH Lock and Key Register (FLKEY) must be written with the correct key codes, in
sequence, before FLASH operations may be performed. The key codes are: 0xA5, 0xF1. The timing does not matter,
but the codes must be written in order. If the key codes are written out of order, or the wrong codes are written,
FLASH writes and erases will be disabled until the next system reset. FLASH writes and erases will also be disabled
if a FLASH write or erase is attempted before the key codes have been written properly. The FLASH lock resets after
each write or erase; the key codes must be written again before a following FLASH operation can be performed. The
FLKEY register is detailed in Figure 10.3.

10.1.2. FLASH Erase Procedure

The FLASH memory can be programmed by software using the MOVX instruction with the address and data byte to
be programmed provided as normal operands. Before writing to FLASH memory using MOVX, FLASH write opera-
tions must be enabled by: (1) setting the PSWE Program Store Write Enable bit (PSCTL.0) to logic 1 (this directs the
MOVX writes to target FLASH memory); and (2) Writing the FLASH key codes in sequence to the FLASH Lock
register (FLKEY). The PSWE bit remains set until cleared by software.

A write to FLASH memory can clear bits but cannot set them; only an erase operation can set bits in FLASH. A byte
location to be programmed should be erased before a new value is written. The 8k byte FLASH memory is orga-
nized in 512-byte pages. The erase operation applies to an entire page (setting all bytes in the page to 0xFF). To erase
an entire 512-byte page, perform the following steps:

Step 5. Disable interrupts (recommended).
Step 6. Set the Program Store Erase Enable bit (PSEE in the PSCTL register).
Step 7. Set the Program Store Write Enable bit (PSWE in the PSCTL register).
Step 8. Write the first key code to FLKEY: 0xA5.
Step 9. Write the second key code to FLKEY: 0xF1.
Step 10. Using the MOVX instruction, write a data byte to any location within the 512-byte page to be

erased.

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10.1.3. FLASH Write Procedure

FLASH bytes are programmed by software with the following sequence:

Step 1. Disable interrupts (recommended).
Step 2. Erase the 512-byte FLASH page containing the target location, as described in

Section 10.1.2

Step 3. Set the PSWE bit in PSCTL.
Step 4. Clear the PSEE bit in PSCTL.
Step 5. Write the first key code to FLKEY: 0xA5.
Step 6. Write the second key code to FLKEY: 0xF1.
Step 7. Using the MOVX instruction, write a single data byte to the desired location within the 512-byte

sector.

Steps 5-7 must be repeated for each byte to be written. After FLASH writes are complete, PSWE should be cleared so
that MOVX instructions do not target program memory.

Table 10.1. FLASH Electrical Characteristics

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

FLASH Size

C8051F300/1/2/3

8192

bytes

FLASH Size

C8051F304

4096

bytes

FLASH Size

C8051F305

2048

bytes

Endurance

20k

100k

Erase/Write

Erase Cycle Time

25 MHz System Clock

Write Cycle Time

25 MHz System Clock

µs

SYSCLK Frequency

(FLASH writes from

application code)

100

kHz

Note: 512 bytes at location 0x1E00 to 0x1FFF are reserved for factory use

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10.2.

Non-volatile Data Storage

The FLASH memory can be used for non-volatile data storage as well as program code. This allows data such as cal-
ibration coefficients to be calculated and stored at run time. Data is written using the MOVX instruction and read
using the MOVC instruction.

10.3.

Security Options

The CIP-51 provides security options to protect the FLASH memory from inadvertent modification by software as
well as to prevent the viewing of proprietary program code and constants. The Program Store Write Enable (bit
PSWE in register PSCTL) and the Program Store Erase Enable (bit PSEE in register PSCTL) bits protect the FLASH
memory from accidental modification by software. PSWE must be explicitly set to `1' before software can modify
the FLASH memory; both PSWE and PSEE must be set to `1' before software can erase FLASH memory. Additional
security features prevent proprietary program code and data constants from being read or altered across the C2 inter-
face.

A security lock byte stored at the last byte of FLASH user space protects the FLASH program memory from being
read or altered across the C2 interface. See Table 10.2 for the security byte description; see Figure 10.1 for a program
memory map and the security byte locations for each device.

The lock bits can always be read and cleared to logic 0 regardless of the security settings.

Important note: The only means of removing a lock (write or read/write) once set is to erase the entire pro-
gram memory space via a C2 Device Erase command.

Table 10.2. Security Byte Decoding

Bits

Description

7-4

Write Lock: Clearing any of these bits to logic 0 prevents all FLASH
memory from being written or page-erased across the C2 interface

3-0

Read/Write Lock: Clearing any of these bits to logic 0 prevents all FLASH
memory from being read, written, or page-erased across the C2 interface.

C8051F300/1/2/3

0x0000

0x1DFF

Lock Byte

Reserved

0x1DFE

FLASH memory

organized in 512-byte

pages

0x1E00

0x0000

0x0FFF

Reserved

0x0FFE

FLASH memory

organized in 512-byte

pages

0x1000

0x0000

0x07FF

Lock Byte

Reserved

0x07FE

FLASH memory

organized in 512-byte

pages

0x0800

Lock Byte

C8051F304

C8051F305

Figure 10.1. FLASH Program Memory Map

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Bits7-2:

UNUSED: Read = 000000b, Write = don't care.

Bit1:

PSEE: Program Store Erase Enable
Setting this bit (in combination with PSWE) allows an entire page of FLASH program memory to be
erased. If this bit is logic 1 and FLASH writes are enabled (PSWE is logic 1), a write to FLASH
memory using the MOVX instruction will erase the entire page that contains the location addressed
by the MOVX instruction. The value of the data byte written does not matter.
0: FLASH program memory erasure disabled.
1: FLASH program memory erasure enabled.

Bit0:

PSWE: Program Store Write Enable
Setting this bit allows writing a byte of data to the FLASH program memory using the MOVX
instruction. The FLASH location should be erased before writing data.
0: Writes to FLASH program memory disabled.
1: Writes to FLASH program memory enabled; the MOVX instruction targets FLASH memory.

R/W

Reset Value

PSEE

PSWE

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0x8F

Figure 10.2. PSCTL: Program Store R/W Control

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Figure 10.3. FLKEY: FLASH Lock and Key Register

Bits7-0:

FLKEY: FLASH Lock and Key Register
Write:
This register must be written to before FLASH writes or erases can be performed. FLASH remains
locked until this register is written to with the following key codes: 0xA5, 0xF1. The timing of the
writes does not matter, as long as the codes are written in order. The key codes must be written for
each FLASH write or erase operation. FLASH will be locked until the next system reset if the wrong
codes are written or if a FLASH operation is attempted before the codes have been written correctly.
Read:
When read, bits 1-0 indicate the current FLASH lock state.
00: FLASH is write/erase locked.
01: The first key code has been written (0xA5).
10: FLASH is unlocked (writes/erases allowed).
11: FLASH writes/erases disabled until the next reset.

R/W

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xB7

Figure 10.4. FLSCL: FLASH Scale Register

Bits7:

FOSE: FLASH One-shot Enable
This bit enables the 50 ns FLASH read one-shot. When the FLASH one-shot disabled, the FLASH
sense amps are enabled for a full clock cycle during FLASH reads.
0: FLASH one-shot disabled.
1: FLASH one-shot enabled.

Bits6-0:

RESERVED. Read = 0. Must Write 0.

R/W

Reset Value

FOSE

Reserved

10000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xB6

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11.

OSCILLATORS

C8051F300/1/2/3/4/5 devices include a programmable internal oscillator and an external oscillator drive circuit. The
internal oscillator can be enabled/disabled and calibrated using the OSCICN and OSCICL registers, as shown in
Figure 11.1. The system clock can be sourced by the external oscillator circuit, the internal oscillator, or a scaled ver-
sion of the internal oscillator. The internal oscillator's electrical specifications are given in Table 11.1 on page 91.

11.1.

Programmable Internal Oscillator

All C8051F300/1/2/3/4/5 devices include a programmable internal oscillator that defaults as the system clock after a
system reset. The internal oscillator period can be adjusted via the OSCICL register as defined by Figure 11.2. On
C8051F300/1 devices, OSCICL is factory calibrated to obtain a 24.5 MHz frequency. On C8051F302/3/4/5 devices,
the oscillator frequency is a nominal 20 MHz and may vary ±20% from device-to-device.

Electrical specifications for the precision internal oscillator are given in Table 11.1 on page 91. The programmed
internal oscillator frequency must not exceed 25 MHz. Note that the system clock may be derived from the pro-
grammed internal oscillator divided by 1, 2, 4, or 8, as defined by the IFCN bits in register OSCICN. The divide value
defaults to 8 following a reset.

Figure 11.1. Oscillator Diagram

OSC

Programmable

Internal Clock

Generator

Input

Circuit

SYSCLK

OSCICL

OSCICN

IOS

CN1

CN0

XTAL1

XTAL2

Option 2

VDD

XTAL2

Option 1

10M

Option 3

XTAL2

Option 4

XTAL2

OSCXCN

XFCN

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Figure 11.2. OSCICL: Internal Oscillator Calibration Register

Bit7:

UNUSED. Read = 0. Write = don't care.

Bits 6-0:

OSCICL: Internal Oscillator Calibration Register.
This register calibrates the internal oscillator period. The reset value for OSCICL defines the internal
oscillator base frequency. On C8051F300/1 devices, the reset value is factory calibrated to generate
an internal oscillator frequency of 24.5 MHz.

R/W

Reset Value

Variable

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xB3

Figure 11.3. OSCICN: Internal Oscillator Control Register

Bits7-5:

UNUSED. Read = 000b, Write = don't care.

Bit4:

IFRDY: Internal Oscillator Frequency Ready Flag.
0: Internal Oscillator is not running at programmed frequency.
1: Internal Oscillator is running at programmed frequency.

Bit3:

CLKSL: System Clock Source Select Bit.
0: SYSCLK derived from the Internal Oscillator, and scaled as per the IFCN bits.
1: SYSCLK derived from the External Oscillator circuit.

Bit2:

IOSCEN: Internal Oscillator Enable Bit.
0: Internal Oscillator Disabled.
1: Internal Oscillator Enabled.

Bits1-0:

IFCN1-0: Internal Oscillator Frequency Control Bits.
00: SYSCLK derived from Internal Oscillator divided by 8.
01: SYSCLK derived from Internal Oscillator divided by 4.
10: SYSCLK derived from Internal Oscillator divided by 2.
11: SYSCLK derived from Internal Oscillator divided by 1.

R/W

Reset Value

IFRDY

CLKSL

IOSCEN

IFCN1

IFCN0

00010100

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xB2

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11.2.

External Oscillator Drive Circuit

The external oscillator circuit may drive an external crystal, ceramic resonator, capacitor, or RC network. A CMOS
clock may also provide a clock input. For a crystal or ceramic resonator configuration, the crystal/resonator must be
wired across the XTAL1 and XTAL2 pins as shown in Option 1 of Figure 11.1. A 10 M

resistor also must be wired

across the XTAL2 and XTAL1 pins for the crystal/resonator configuration. In RC, capacitor, or CMOS clock config-
uration, the clock source should be wired to the XTAL2 pin as shown in Option 2, 3, or 4 of Figure 11.1. The type of
external oscillator must be selected in the OSCXCN register, and the frequency control bits (XFCN) must be selected
appropriately (see Figure 11.4).

Important Note on External Oscillator Usage: Port pins must be configured when using the external oscillator cir-
cuit. When the external oscillator drive circuit is enabled in crystal/resonator mode, Port pins P0.2 and P0.3 are occu-
pied as XTAL1 and XTAL2 respectively. When the external oscillator drive circuit is enabled in capacitor, RC, or
CMOS clock mode, Port pin P0.3 is occupied as XTAL2. The Port I/O Crossbar should be configured to skip the
occupied Port pins; see

Section "12.1. Priority Crossbar Decoder" on page 96

for Crossbar configuration. Addi-

tionally, when using the external oscillator circuit in crystal/resonator, capacitor, or RC mode, the associated Port pins
should be configured as analog inputs. In CMOS clock mode, the associated pin should be configured as a digital
input. See

Section "12.2. Port I/O Initialization" on page 98

for details on Port input mode selection.

11.3.

System Clock Selection

The CLKSL bit in register OSCICN selects which oscillator is used as the system clock. CLKSL must be set to `1' for
the system clock to run from the external oscillator; however the external oscillator may still clock peripherals (tim-
ers, PCA) when the internal oscillator is selected as the system clock. The system clock may be switched on-the-fly
between the internal and external oscillator, so long as the selected oscillator is enabled and has settled. The internal
oscillator requires little start-up time and may be enabled and selected as the system clock in the same write to
OSCICN. External crystals and ceramic resonators typically require a start-up time before they are settled and ready
for use as the system clock. The Crystal Valid Flag (XTLVLD in register OSCXCN) is set to `1' by hardware when
the external oscillator is settled. To avoid reading a false XTLVLD, in crystal mode software should delay at least
1 ms between enabling the external oscillator and checking XTLVLD. RC and C modes typically require no startup
time.

Table 11.1. Internal Oscillator Electrical Characteristics

-40°C to +85°C unless otherwise specified

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Calibrated Internal Oscillator

Frequency

C8051F300/1 devices

24.5

MHz

Uncalibrated Internal Oscillator

Frequency

C8051F302/3/4/5 devices

MHz

Internal Oscillator Supply Current

(from VDD)

OSCICN.2 = 1

450

µA

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Figure 11.4. OSCXCN: External Oscillator Control Register

Bit7:

XTLVLD: Crystal Oscillator Valid Flag.
(Read only when XOSCMD = 11x.)
0: Crystal Oscillator is unused or not yet stable.
1: Crystal Oscillator is running and stable.

Bits6-4:

XOSCMD2-0: External Oscillator Mode Bits.
00x: External Oscillator circuit off.
010: External CMOS Clock Mode.
011: External CMOS Clock Mode with divide by 2 stage.
100: RC Oscillator Mode with divide by 2 stage.
101: Capacitor Oscillator Mode with divide by 2 stage.
110: Crystal Oscillator Mode.
111: Crystal Oscillator Mode with divide by 2 stage.

Bit3:

RESERVED. Read = 0, Write = don't care.

Bits2-0:

XFCN2-0: External Oscillator Frequency Control Bits.
000-111: See table below:

CRYSTAL MODE (Circuit from Figure 11.1, Option 1; XOSCMD = 11x)

Choose XFCN value to match crystal frequency.

RC MODE (Circuit from Figure 11.1, Option 2; XOSCMD = 10x)

Choose XFCN value to match frequency range:

f = 1.23(10

) / (R * C), where

f = frequency of oscillation in MHz
C = capacitor value in pF
R = Pull-up resistor value in k

C MODE (Circuit from Figure 11.1, Option 3; XOSCMD = 10x)

Choose K Factor (KF) for the oscillation frequency desired:
f = KF / (C * VDD), where
f = frequency of oscillation in MHz
C = capacitor value the XTAL2 pin in pF
VDD = Power Supply on MCU in volts

R/W

Reset Value

XTLVLD XOSCMD2 XOSCMD1 XOSCMD0

XFCN2

XFCN1

XFCN0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xB1

XFCN

Crystal (XOSCMD = 11x)

RC (XOSCMD = 10x)

C (XOSCMD = 10x)

000

32kHz

25kHz

K Factor = 0.87

001

32kHz

< f 84kHz

25kHz

< f 50kHz

K Factor = 2.6

010

84kHz

< f 225kHz

50kHz

< f 100kHz

K Factor = 7.7

011

225kHz

< f 590kHz

100kHz

< f 200kHz

K Factor = 22

100

590kHz

< f 1.5MHz

200kHz

< f 400kHz

K Factor = 65

101

1.5MHz

< f 4MHz

400kHz

< f 800kHz

K Factor = 180

110

4MHz

< f 10MHz

800kHz

< f 1.6MHz

K Factor = 664

111

10MHz

< f 30MHz

1.6MHz

< f 3.2MHz

K Factor = 1590

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11.4.

External Crystal Example

If a crystal or ceramic resonator is used as an external oscillator source for the MCU, the circuit should be configured
as shown in Figure 11.1, Option 1. The External Oscillator Frequency Control value (XFCN) should be chosen from
the Crystal colum of the table in Figure 11.4 (OSCXCN register). For example, an 11.0592 MHz crystal requires an
XFCN setting of 111b.

When the crystal oscillator is first enabled, the oscillator amplitude detection circuit requires a settling time to
achieve proper bias. Introducing a delay of 1 ms between enabling the oscillator and checking the XTLVLD bit will
prevent a premature switch to the external oscillator as the system clock. Switching to the external oscillator before
the crystal oscillator has stabilized can result in unpredictable behavior. The recommended procedure is:

Step 1. Enable the external oscillator.
Step 2. Wait at least 1 ms.
Step 3. Poll for XTLVLD => `1'.
Step 4. Switch the system clock to the external oscillator.

Important Note on External Crystals: Crystal oscillator circuits are quite sensitive to PCB layout. The crystal
should be placed as close as possible to the XTAL pins on the device. The traces should be as short as possible and
shielded with ground plane from any other traces which could introduce noise or interference.

11.5.

External RC Example

If an RC network is used as an external oscillator source for the MCU, the circuit should be configured as shown in
Figure 11.1, Option 2. The capacitor should be no greater than 100 pF; however for very small capacitors, the total
capacitance may be dominated by parasitic capacitance in the PCB layout. To determine the required External Oscil-
lator Frequency Control value (XFCN) in the OSCXCN Register, first select the RC network value to produce the
desired frequency of oscillation. If the frequency desired is 100 kHz, let R = 246 k

and C = 50 pF:

f = 1.23( 10

) / RC = 1.23 ( 10

) / [ 246 * 50 ] = 0.1 MHz = 100 kHz

Referring to the table in Figure 11.4, the required XFCN setting is 010b.

11.6.

External Capacitor Example

If a capacitor is used as an external oscillator for the MCU, the circuit should be configured as shown in Figure 11.1,
Option 3. The capacitor should be no greater than 100 pF; however for very small capacitors, the total capacitance
may be dominated by parasitic capacitance in the PCB layout. To determine the required External Oscillator Fre-
quency Control value (XFCN) in the OSCXCN Register, select the capacitor to be used and find the frequency of
oscillation from the equations below. Assume VDD = 3.0 V and C = 50 pF:

f = KF / ( C * VDD ) = KF / ( 50 * 3 ) MHz
f = KF / 150 MHz

If a frequency of roughly 150 kHz is desired, select the K Factor from the table in Figure 11.4 as KF = 22:

f = 22 / 150 = 0.146 MHz, or 146 kHz

Therefore, the XFCN value to use in this example is 011b.

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12.

PORT INPUT/OUTPUT

Digital and analog resources are available through a byte-wide digital I/O Port, Port0. Each of the Port pins can be
defined as general-purpose I/O (GPIO), analog input, or assigned to one of the internal digital resources as shown in
Figure 12.3. The designer has complete control over which functions are assigned, limited only by the number of
physical I/O pins. This resource assignment flexibility is achieved through the use of a Priority Crossbar Decoder.
Note that the state of a Port I/O pin can always be read in the corresponding Port latch, regardless of the Crossbar set-
tings.

The Crossbar assigns the selected internal digital resources to the I/O pins based on the Priority Decoder (Figure 12.3
and Figure 12.4). The registers XBR0, XBR1, and XBR2, defined in Figure 12.5, Figure 12.6, and Figure 12.7 are
used to select internal digital functions.

All Port I/Os are 5 V tolerant (refer to Figure 12.2 for the Port cell circuit). The Port I/O cells are configured as either
push-pull or open-drain in the Port0 Output Mode register (P0MDOUT). Complete Electrical Specifications for Port
I/O are given in Table 12.1 on page 102.

Figure 12.1. Port I/O Functional Block Diagram

XBR0, XBR1,

XBR2 Registers

Digital

Crossbar

Priority

Decoder

SYSCLK

(
I
nter

nal

Digit

ignals

)

Highest

Priority

Lowest
Priority

P0
I/O

Cells

P0.0

P0.7

P0MDOUT,

P0MDIN Registers

SMBus

UART

T0, T1

PCA

Port Latch

(P0.0-P0.7)

CP0

Outputs

Figure 12.2. Port I/O Cell Block Diagram

GND

/PORT-OUTENABLE

PORT-OUTPUT

PUSH-PULL

VDD

/WEAK-PULLUP

(WEAK)

PORT
PAD

ANALOG INPUT

Analog Select

PORT-INPUT

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12.1.

Priority Crossbar Decoder

The Priority Crossbar Decoder (Figure 12.3) assigns a priority to each I/O function, starting at the top with UART0.
When a digital resource is selected, the least-significant unassigned Port pin is assigned to that resource (excluding
UART0, which is always at pins 4 and 5). If a Port pin is assigned, the Crossbar skips that pin when assigning the next
selected resource. Additionally, the Crossbar will skip Port pins whose associated bits in the XBR0 register are set.
The XBR0 register allows software to skip Port pins that are to be used for analog input or GPIO.

Important Note on Crossbar Configuration: If a Port pin is claimed by a peripheral without use of the Crossbar, its
corresponding XBR0 bit should be set. This applies to P0.0 if VREF is enabled, P0.3 and/or P0.2 if the external oscil-
lator circuit is enabled, P0.6 if the ADC is configured to use the external conversion start signal (CNVSTR), and any
selected ADC or Comparator inputs. The Crossbar skips selected pins as if they were already assigned, and moves to
the next unassigned pin. Figure 12.3 shows the Crossbar Decoder priority with no Port pins skipped (XBR0 = 0x00);
Figure 12.4 shows the Crossbar Decoder priority with pins 6 and 2 skipped (XBR0 = 0x44).

Figure 12.3. Crossbar Priority Decoder with XBR0 = 0x00

VREF

CNVSTR

CEX2

CP0A

SYSCLK

CEX0

CEX1

Signa

Una

ila

ble

SF Signals
PIN I/O

TX0

RX0

SDA

SCL

CP0

Port pin potentially available to peripheral

SF Signals

ECI

XBR0[0:7]

Special Function Signals are not assigned by the crossbar.
When these signals are enabled, the CrossBar must be
manually configured to skip their corresponding port pins.
Note: x1 refers to the XTAL1 signal; x2 refers to the XTAL2
signal.

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Registers XBR1 and XBR2 are used to assign the digital I/O resources to the physical I/O Port pins. Note that when
the SMBus is selected, the Crossbar assigns both pins associated with the SMBus (SDA and SCL). Either or both of
the UART signals may be selected by the Crossbar. UART0 pin assignments are fixed for bootloading purposes:
when UART TX0 is selected, it is always assigned to P0.4; when UART RX0 is selected, it is always assigned to
P0.5. Standard Port I/Os appear contiguously after the prioritized functions have been assigned. For example, if
assigned functions that take the first 3 Port I/O (P0.[2:0]), 5 Port I/O are left for analog or GPIO use.

Figure 12.4. Crossbar Priority Decoder with XBR0 = 0x44

VREF

CNVSTR

Port pin potentially available to peripheral

Port pin skipped by CrossBar

Signa

Una

ila

ble

RX0

SDA

SCL

CP0

CEX0

CEX1

Special Function Signals are not assigned by the crossbar. When
these signals are enabled, the CrossBar must be manually
configured to skip their corresponding port pins. Note: x1 refers to
the XTAL1 signal; x2 refers to the XTAL2 signal.

SF Signals

CEX2

ECI

CP0A

SYSCLK

XBR0[0:7]

SF Signals
PIN I/O

TX0

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12.2.

Port I/O Initialization

Port I/O initialization consists of the following steps:

Step 1. Select the input mode (analog or digital) for all Port pins, using the Port0 Input Mode register

(P0MDIN).

Step 2. Select the output mode (open-drain or push-pull) for all Port pins, using the Port0 Output Mode

Step 3. Set XBR0 to skip any pins selected as analog inputs or special functions.
Step 4. Assign Port pins to desired peripherals.
Step 5. Enable the Crossbar.

All Port pins must be configured as either analog or digital inputs. Any pins to be used as Comparator or ADC inputs
should be configured as an analog inputs. When a pin is configured as an analog input, its weak pull-up, digital driver,
and digital receiver is disabled. This process saves power and reduces noise on the analog input. Pins configured as
digital inputs may still be used by analog peripherals; however this practice is not recommended.

Additionally, all analog input pins should be configured to be skipped by the Crossbar (accomplished by setting the
associated bits in XBR0). Port input mode is set in the P0MDIN register, where a `1' indicates a digital input, and a
`0' indicates an analog input. All pins default to digital inputs on reset. See Figure 12.9 for the P0MDIN register
details.

The output driver characteristics of the I/O pins are defined using the Port0 Output Mode register P0MDOUT (see
Figure 12.10). Each Port Output driver can be configured as either open drain or push-pull. This selection is required
even for the digital resources selected in the XBRn registers, and is not automatic. The only exception to this is the
SMBus (SDA, SCL) pins, which are configured as open-drain regardless of the P0MDOUT settings. When the
WEAKPUD bit in XBR2 is `0', a weak pull-up is enabled for all Port I/O configured as open-drain. WEAKPUD does
not affect the push-pull Port I/O. Furthermore, the weak pull-up is turned off on an open-drain output that is driving a
`0' to avoid unnecessary power dissipation.

Registers XBR0, XBR1 and XBR2 must be loaded with the appropriate values to select the digital I/O functions
required by the design. Setting the XBARE bit in XBR2 to `1' enables the Crossbar. Until the Crossbar is enabled, the
external pins remain as standard digital inputs (output drivers disabled) regardless of the XBRn Register settings. For
given XBRn Register settings, one can determine the I/O pin-out using the Priority Decode Table; as an alternative,
the Configuration Wizard utility of the Cygnal IDE software will determine the Port I/O pin-assignments based on the
XBRn Register settings.

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Figure 12.5. XBR0: Port I/O Crossbar Register 0

Bit7:

UNUSED. Read = 0b; Write = don't care.

Bits6-0:

XSKP[6:0]: Crossbar Skip Enable Bits
These bits select Port pins to be skipped by the Crossbar Decoder. Port pins used as analog inputs (for
ADC or Comparator) or used as special functions (VREF input, external oscillator circuit, CNVSTR
input) should be skipped by the Crossbar.
0: Corresponding P0.n pin is not skipped by the Crossbar.
1: Corresponding P0.n pin is skipped by the Crossbar.

R/W

Reset Value

XSKP6

XSKP5

XSKP4

XSKP3

XSKP2

XSKP1

XSKP0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xE1

Figure 12.6. XBR1: Port I/O Crossbar Register 1

Bits7-6:

PCA0ME: PCA Module I/0 Enable Bits
00: All PCA I/O unavailable at Port pins.
01: CEX0 routed to Port pin.
10: CEX0, CEX1 routed to Port pins.
11: CEX0, CEX1, CEX2 routed to Port pins.

Bit5:

CP0AOEN: Comparator0 Asynchronous Output Enable
0: Asynchronous CP0 unavailable at Port pin.
1: Asynchronous CP0 routed to Port pin.

Bit4:

CP0OEN: Comparator0 Output Enable
0: CP0 unavailable at Port pin.
1: CP0 routed to Port pin.

Bit3:

SYSCKE: /SYSCLK Output Enable
0: /SYSCLK unavailable at Port pin.
1: /SYSCLK output routed to Port pin.

Bit2:

SMB0OEN: SMBus I/O Enable
0: SMBus I/O unavailable at Port pins.
1: SDA, SCL routed to Port pins.

Bit1:

URX0EN: UART RX Enable
0: UART RX0 unavailable at Port pin.
1: UART RX0 routed to Port pin P0.5.

Bit0:

UTX0EN: UART TX Output Enable
0: UART TX0 unavailable at Port pin.
1: UART TX0 routed to Port pin P0.4.

R/W

Reset Value

PCA0ME

CP0AOEN CP0OEN

SYSCKE SMB0OEN URX0EN

UTX0EN

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xE2

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12.3.

General Purpose Port I/O

Port pins that remain unassigned by the Crossbar and are not used by analog peripherals can be used for general pur-
pose I/O. Port0 is accessed through a corresponding special function register (SFR) that is both byte addressable and
bit addressable. When writing to a Port, the value written to the SFR is latched to maintain the output data value at
each pin. When reading, the logic levels of the Port's input pins are returned regardless of the XBRn settings (i.e.,
even when the pin is assigned to another signal by the Crossbar, the Port register can always read its corresponding
Port I/O pin). The exception to this is the execution of the read-modify-write instructions. The read-modify-write
instructions when operating on a Port SFR are the following: ANL, ORL, XRL, JBC, CPL, INC, DEC, DJNZ and
MOV, CLR or SET, when the destination is an individual bit in a Port SFR. For these instructions, the value of the
register (not the pin) is read, modified, and written back to the SFR.

Figure 12.8. P0: Port0 Register

Bits7-0:

P0.[7:0]
Write - Output appears on I/O pins per XBR0, XBR1, and XBR2 Registers
0: Logic Low Output.
1: Logic High Output (open-drain if corresponding P0MDOUT.n bit = 0)
Read - Always reads `1' if selected as analog input in register P0MDIN. Directly reads Port pin when
configured as digital input.
0: P0.n pin is logic low.
1: P0.n pin is logic high.

R/W

Reset Value

P0.7

P0.6

P0.5

P0.4

P0.3

P0.2

P0.1

P0.0

11111111

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

(bit addressable)

0x80

Figure 12.9. P0MDIN: Port0 Input Mode Register

Bits7-0:

Input Configuration Bits for P0.7-P0.0 (respectively)
Port pins configured as analog inputs have their weak pull-up, digital driver, and digital receiver dis-
abled.
0: Corresponding P0.n pin is configured as an analog input.
1: Corresponding P0.n pin is configured as a digital input.

R/W

Reset Value

11111111

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xF1

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Table 12.1. Port I/O DC Electrical Characteristics

VDD = 2.7 to 3.6V, -40°C to +85°C unless otherwise specified
PARAMETERS

CONDITIONS

MIN

TYP

MAX

UNITS

Output High Voltage

= -3mA, Port I/O push-pull

= -10µA, Port I/O push-pull

= -10mA, Port I/O push-pull

VDD-0.7
VDD-0.1

VDD-0.8

Output Low Voltage

= 8.5mA

= 10µA

= 25mA

1.0

0.6
0.1

Input High Voltage

2.0

Input Low Voltage

0.8

Input Leakage Current

Weak Pull-up Off

Weak Pull-up On, V

= 0 V

±1
40

µA

Figure 12.10. P0MDOUT: Port0 Output Mode Register

Bits7-0:

Output Configuration Bits for P0.7-P0.0 (respectively): ignored if corresponding bit in register
P0MDIN is logic 0.
0: Corresponding P0.n Output is open-drain.
1: Corresponding P0.n Output is push-pull.

(Note: When SDA and SCL appear on any of the Port I/O, each are open-drain regardless of the value
of P0MDOUT).

R/W

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xA4

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13.

SMBUS

The SMBus I/O interface is a two-wire, bi-directional serial bus. The SMBus is compliant with the System Manage-

ment Bus Specification, version 1.1, and compatible with the I

C serial bus. Reads and writes to the interface by the

system controller are byte oriented with the SMBus interface autonomously controlling the serial transfer of the data.
Data can be transferred at up to 1/10th of the system clock operating as master or slave (this can be faster than
allowed by the SMBus specification, depending on the system clock used). A method of extending the clock-low
duration is available to accommodate devices with different speed capabilities on the same bus.

The SMBus interface may operate as a master and/or slave, and may function on a bus with multiple masters. The
SMBus provides control of SDA (serial data), SCL (serial clock) generation and synchronization, arbitration logic,
and START/STOP control and generation. Three SFRs are associated with the SMBus: SMB0CF configures the
SMBus; SMB0CN controls the status of the SMBus; and SMB0DAT is the data register, used for both transmitting
and receiving SMBus data and slave addresses.

Figure 13.1. SMBus Block Diagram

Data Path

Control

SMBUS CONTROL LOGIC

C
R
O
S
S
B
A
R

SCL

FILTER

SDA

Control

SCL

Control

Arbitration
SCL Synchronization

IRQ Generation

SCL Generation (Master Mode)
SDA Control

Interrupt
Request

Port I/O

SMB0CN

S
T
A

A
C
K
R

A
R
B

S
T

A
C
K

T
X

M
O
D

A
S
T
E
R

S
T

T0 Overflow

T1 Overflow

TMR2H Overflow

TMR2L Overflow

SMB0CF

E
N
S

N
H

B
U
S
Y

E
X
T
H
O

B
T
O
E

B
F
T
E

B
C
S

SMB0DAT

SDA

FILTER

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13.1.

Supporting Documents

It is assumed the reader is familiar with or has access to the following supporting documents:

The I

C-Bus and How to Use It (including specifications), Philips Semiconductor.

The I

C-Bus Specification -- Version 2.0, Philips Semiconductor.

System Management Bus Specification -- Version 1.1, SBS Implementers Forum.

13.2.

SMBus Configuration

Figure 13.2 shows a typical SMBus configuration. The SMBus specification allows any recessive voltage between
3.0 V and 5.0 V; different devices on the bus may operate at different voltage levels. The bi-directional SCL (serial
clock) and SDA (serial data) lines must be connected to a positive power supply voltage through a pull-up resistor or
similar circuit. Every device connected to the bus must have an open-drain or open-collector output for both the SCL
and SDA lines, so that both are pulled high (recessive state) when the bus is free. The maximum number of devices
on the bus is limited only by the requirement that the rise and fall times on the bus not exceed 300 ns and 1000 ns,
respectively.

Figure 13.2. Typical SMBus Configuration

VDD = 5V

Master
Device

Slave

Device 1

Slave

Device 2

VDD = 3V

VDD = 5V

VDD = 3V

SDA

SCL

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13.3.

SMBus Operation

Two types of data transfers are possible: data transfers from a master transmitter to an addressed slave receiver
(WRITE), and data transfers from an addressed slave transmitter to a master receiver (READ). The master device ini-
tiates both types of data transfers and provides the serial clock pulses on SCL. The SMBus interface may operate as a
master or a slave, and multiple master devices on the same bus are supported. If two or more masters attempt to ini-
tiate a data transfer simultaneously, an arbitration scheme is employed with a single master always winning the arbi-
tration. Note that it is not necessary to specify one device as the Master in a system; any device that transmits a
START and a slave address becomes the master for the duration of that transfer.

A typical SMBus transaction consists of a START condition followed by an address byte (Bits7-1: 7-bit slave
address; Bit0: R/W direction bit), one or more bytes of data, and a STOP condition. Each byte that is received (by a
master or slave) must be acknowledged (ACK) with a low SDA during a high SCL (see Figure 13.3). If the receiving
device does not ACK, the transmitting device will read a NACK (not acknowledge), which is a high SDA during a
high SCL.

The direction bit (R/W) occupies the least-significant bit position of the address byte. The direction bit is set to
logic 1 to indicate a "READ" operation and cleared to logic 0 to indicate a "WRITE" operation.

All transactions are initiated by a master, with one or more addressed slave devices as the target. The master gener-
ates the START condition and then transmits the slave address and direction bit. If the transaction is a WRITE opera-
tion from the master to the slave, the master transmits the data a byte at a time waiting for an ACK from the slave at
the end of each byte. For READ operations, the slave transmits the data waiting for an ACK from the master at the
end of each byte. At the end of the data transfer, the master generates a STOP condition to terminate the transaction
and free the bus. Figure 13.3 illustrates a typical SMBus transaction.

13.3.1. Arbitration

A master may start a transfer only if the bus is free. The bus is free after a STOP condition or after the SCL and SDA
lines remain high for a specified time (see

Section "13.3.4. SCL High (SMBus Free) Timeout" on page 106

). In the

event that two or more devices attempt to begin a transfer at the same time, an arbitration scheme is employed to
force one master to give up the bus. The master devices continue transmitting until one attempts a HIGH while the
other transmits a LOW. Since the bus is open-drain, the bus will be pulled LOW. The master attempting the HIGH
will detect a LOW SDA and lose the arbitration. The winning master continues its transmission without interruption;
the losing master becomes a slave and receives the rest of the transfer if addressed. This arbitration scheme is non-
destructive: one device always wins, and no data is lost.

Figure 13.3. SMBus Transaction

SLA6

SDA

SLA5-0

R/W

D6-0

SCL

Slave Address + R/W

Data Byte

START

ACK

NACK

STOP

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13.3.2. Clock Low Extension

SMBus provides a clock synchronization mechanism, similar to I

C, which allows devices with different speed capa-

bilities to coexist on the bus. A clock-low extension is used during a transfer in order to allow slower slave devices to
communicate with faster masters. The slave may temporarily hold the SCL line LOW to extend the clock low period,
effectively decreasing the serial clock frequency.

13.3.3. SCL Low Timeout

If the SCL line is held low by a slave device on the bus, no further communication is possible. Furthermore, the mas-
ter cannot force the SCL line high to correct the error condition. To solve this problem, the SMBus protocol specifies
that devices participating in a transfer must detect any clock cycle held low longer than 25 ms as a "timeout" condi-
tion. Devices that have detected the timeout condition must reset the communication no later than 10 ms after detect-
ing the timeout condition.

When the SMBTOE bit in SMB0CF is set, Timer 2 is used to detect SCL low timeouts. Timer 2 is forced to reload
when SCL is high, and allowed to count when SCL is low. With Timer 2 enabled and configured to overflow after
25 ms (and SMBTOE set), the Timer 2 interrupt service routine can be used to reset (disable and re-enable) the
SMBus in the event of an SCL low timeout. Timer 2 configuration details can be found in

Section "15.2. Timer 2"

on page 141

13.3.4. SCL High (SMBus Free) Timeout

The SMBus specification stipulates that if the SCL and SDA lines remain high for more that 50 µs, the bus is desig-
nated as free. When the SMBFTE bit in SMB0CF is set, the bus will be considered free if SCL and SDA remain high
for more than 10 SMBus clock source periods. If the SMBus is waiting to generate a Master START, the START will
be generated following this timeout. Note that a clock source is required for free timeout detection, even in a slave-
only implementation.

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13.4.

Using the SMBus

The SMBus can operate in both Master and Slave modes. The interface provides timing and shifting control for serial
transfers; higher level protocol is determined by user software. The SMBus interface provides the following applica-
tion-independent features:

Byte-wise serial data transfers

Clock signal generation on SCL (Master Mode only) and SDA data synchronization

Timeout/bus error recognition, as defined by the SMB0CF configuration register

START/STOP timing, detection, and generation

Bus arbitration

Interrupt generation

Status information

SMBus interrupts are generated for each data byte or slave address that is transferred. When transmitting, this inter-
rupt is generated after the ACK cycle so that software may read the received ACK value; when receiving data, this
interrupt is generated before the ACK cycle so that software may define the outgoing ACK value. See

Section

"13.5. SMBus Transfer Modes" on page 115

for more details on transmission sequences.

Interrupts are also generated to indicate the beginning of a transfer when a master (START generated), or the end of a
transfer when a slave (STOP detected). Software should read the SMB0CN (SMBus Control register) to find the
cause of the SMBus interrupt. The SMB0CN register is described in

Section "13.4.2. SMB0CN Control Register"

on page 111

; Table 13.4 provides a quick SMB0CN decoding reference.

SMBus configuration options include:

Timeout detection (SCL Low Timeout and/or Bus Free Timeout)

SDA setup and hold time extensions

Slave event enable/disable

Clock source selection

These options are selected in the SMB0CF register, as described in

Section "13.4.1. SMBus Configuration Regis-

ter" on page 108

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13.4.1. SMBus Configuration Register

The SMBus Configuration register (SMB0CF) is used to enable the SMBus Master and/or Slave modes, select the
SMBus clock source, and select the SMBus timing and timeout options. When the ENSMB bit is set, the SMBus is
enabled for all master and slave events. Slave events may be disabled by setting the INH bit. With slave events inhib-
ited, the SMBus interface will still monitor the SCL and SDA pins; however, the interface will NACK all received
addresses and will not generate any slave interrupts. When the INH bit is set, all slave events will be inhibited follow-
ing the next START (interrupts will continue for the duration of the current transfer).

The SMBCS1-0 bits select the SMBus clock source, which is used only when operating as a master or when the Free
Timeout detection is enabled. When operating as a master, overflows from the selected source determine the absolute
minimum SCL low and high times as defined in Equation 13.1. Note that the selected clock source may be shared by
other peripherals so long as the timer is left running at all times. For example, Timer 1 overflows may generate the
SMBus and UART baud rates simultaneously. Timer configuration is covered in

Section "15. Timers" on page 133

The selected clock source should be configured to establish the minimum SCL High and Low times as per
Equation 13.1. When the interface is operating as a master (and SCL is not driven or extended by any other devices
on the bus), the typical SMBus bit rate is approximated by Equation 13.2.

Figure 13.4 shows the typical SCL generation described by Equation 13.2. Notice that T

HIGH

is typically twice as

large as T

LOW

. The actual SCL output may vary due to other devices on the bus (SCL may be extended low by slower

slave devices, or driven low by contending master devices). The bit rate when operating as a master will never exceed
the limits defined by equation Equation 13.1.

Table 13.1. SMBus Clock Source Selection

SMBCS1 SMBCS0 SMBus Clock Source

Timer 0 Overflow

Timer 1 Overflow

Timer 2 High Byte Overflow

Timer 2 Low Byte Overflow

Equation 13.1. Minimum SCL High and Low Times

HighMin

LowMin

ClockSourceOverflow

----------------------------------------------

Equation 13.2. Typical SMBus Bit Rate

BitRate

ClockSourceOverflow

----------------------------------------------

SCL

Timer Source

Overflows

SCL High Timeout

Low

High

Figure 13.4. Typical SMBus SCL Generation

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Setting the EXTHOLD bit extends the minimum setup and hold times for the SDA line. The minimum SDA setup
time defines the absolute minimum time that SDA is stable before SCL transitions from low-to-high. The minimum
SDA hold time defines the absolute minimum time that the current SDA value remains stable after SCL transitions
from high-to-low. EXTHOLD should be set so that the minimum setup and hold times meet the SMBus Specification
requirements of 250 ns and 300 ns, respectively. Table 13.2 shows the minimum setup and hold times for the two
EXTHOLD settings. Setup and hold time extensions are typically necessary when SYSCLK is above 10 MHz.

With the SMBTOE bit set, Timer 2 should be configured to overflow after 25 ms in order to detect SCL low timeouts
(see

Section "13.3.3. SCL Low Timeout" on page 106

). The SMBus interface will force Timer 2 to reload while

SCL is high, and allow Timer 2 to count when SCL is low. The Timer 2 interrupt service routine should be used to
reset SMBus communication by disabling and re-enabling the SMBus. Timer 2 configuration is described in

Section

"15.2. Timer 2" on page 141

SMBus Free Timeout detection can be enabled by setting the SMBFTE bit. When this bit is set, the bus will be con-
sidered free if SDA and SCL remain high for more than 10 SMBus clock source periods (see Figure 13.4). When a
Free Timeout is detected, the interface will respond as if a STOP was detected (an interrupt will be generated, and
STO will be set).

Table 13.2. Minimum SDA Setup and Hold Times

EXTHOLD

Minimum SDA Setup Time

Minimum SDA Hold Time

low

- 4 system clocks

1 system clock + s/w delay

3 system clocks

11 system clocks

12 system clocks

Setup Time for ACK bit transmissions and the MSB of all data transfers. The s/w delay

occurs between the time SMB0DAT or ACK is written and when SI is cleared. Note that if
SI is cleared in the same write that defines the outgoing ACK value, s/w delay is zero.

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Figure 13.5. SMB0CF: SMBus Clock/Configuration Register

Bit7:

ENSMB: SMBus Enable.
This bit enables/disables the SMBus interface. When enabled, the interface constantly monitors the
SDA and SCL pins.
0: SMBus interface disabled.
1: SMBus interface enabled.

Bit6:

INH: SMBus Slave Inhibit.
When this bit is set to logic 1, the SMBus does not generate an interrupt when slave events occur.
This effectively removes the SMBus slave from the bus. Master Mode interrupts are not affected.
0: SMBus Slave Mode enabled.
1: SMBus Slave Mode inhibited.

Bit5:

BUSY: SMBus Busy Indicator.
This bit is set to logic 1 by hardware when a transfer is in progress. It is cleared to logic 0 when a
STOP or free-timeout is sensed.

Bit4:

EXTHOLD: SMBus Setup and Hold Time Extension Enable.
This bit controls the SDA setup and hold times according to Table 13.2.
0: SDA Extended Setup and Hold Times disabled.
1: SDA Extended Setup and Hold Times enabled.

Bit3:

SMBTOE: SMBus SCL Timeout Detection Enable.
This bit enables SCL low timeout detection. If set to logic 1, the SMBus forces Timer 2 to reload
while SCL is high and allows Timer 2 to count when SCL goes low. Timer 2 should be programmed
to generate interrupts at 25 ms, and the Timer 2 interrupt service routine should reset SMBus commu-
nication.

Bit2:

SMBFTE: SMBus Free Timeout Detection Enable.
When this bit is set to logic 1, the bus will be considered free if SCL and SDA remain high for more
than 10 SMBus clock source periods.

Bits1-0:

SMBCS1-SMBCS0: SMBus Clock Source Selection.
These two bits select the SMBus clock source, which is used to generate the SMBus bit rate. The
selected device should be configured according to Equation 13.1.

R/W

Reset Value

ENSMB

INH

BUSY

EXTHOLD SMBTOE

SMBFTE

SMBCS1

SMBCS0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xC1

SMBCS1

SMBCS0

SMBus Clock Source

Timer 0 Overflow

Timer 1 Overflow

Timer 2 High Byte Overflow

Timer 2 Low Byte Overflow

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13.4.2. SMB0CN Control Register

SMB0CN is used to control the interface and to provide status information (see Figure 13.6). The higher four bits of
SMB0CN (MASTER, TXMODE, STA, and STO) form a status vector that can be used to jump to service routines.
MASTER and TXMODE indicate the master/slave state and transmit/receive modes, respectively.

The STA bit indicates that a START has been detected or generated since the last SMBus interrupt. When set to `1',
the STA bit will cause the SMBus to enter Master mode and generate a START when the bus becomes free. STA is
not cleared by hardware after the START is generated; it must be cleared by software.

As a master, writing the STO bit will cause the hardware to generate a STOP condition and end the current transfer
after the next ACK cycle. STO is cleared by hardware after the STOP condition is generated. As a slave, STO indi-
cates that a STOP condition has been detected since the last SMBus interrupt. STO is also used in slave mode to man-
age the transition from slave receiver to slave transmitter; see

Section 13.5.4

for details on this procedure.

If STO and STA are both set to `1' (while in Master Mode), a STOP followed by a START will be generated.

As a receiver, writing the ACK bit defines the outgoing ACK value; as a transmitter, reading the ACK bit indicates
the value received on the last ACK cycle. ACKRQ is set each time a byte is received, indicating that an outgoing
ACK value is needed. When ACKRQ is set, software should write the desired outgoing value to the ACK bit before
clearing SI. A NACK will be generated if software does not write the ACK bit before clearing SI. SDA will reflect
the defined ACK value immediately following a write to the ACK bit; however SCL will remain low until SI is
cleared. If a received slave address is not acknowledged, further slave events will be ignored until the next START is
detected.

The ARBLOST bit indicates that the interface has lost an arbitration. This may occur anytime the interface is trans-
mitting (master or slave). A lost arbitration while operating as a slave indicates a bus error condition. ARBLOST is
cleared by hardware each time SI is cleared.

The SI bit (SMBus Interrupt Flag) is set at the beginning and end of each transfer, after each byte frame, or when an
arbitration is lost; see Table 13.3 for more details.
Important Note About the SI Bit: The SMBus interface is stalled while SI is set; thus SCL is held low, and the bus
is stalled until software clears SI.

Table 13.3 lists all sources for hardware changes to the SMB0CN bits. Refer to Table 13.4 for SMBus status decoding
using the SMB0CN register.

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Figure 13.6. SMB0CN: SMBus Control Register

Bit7:

MASTER: SMBus Master/Slave Indicator.
This read-only bit indicates when the SMBus is operating as a master.
0: SMBus operating in Slave Mode.
1: SMBus operating in Master Mode.

Bit6:

TXMODE: SMBus Transmit Mode Indicator.
This read-only bit indicates when the SMBus is operating as a transmitter.
0: SMBus in Receiver Mode.
1: SMBus in Transmitter Mode.

Bit5:

STA: SMBus Start Flag.
Write:
0: No Start generated.
1: When operating as a master, a START condition is transmitted if the bus is free (If the bus is not
free, the START is transmitted after a STOP is received or a free timeout is detected). If STA is set by
software as an active Master, a repeated START will be generated after the next ACK cycle.
Read:
0: No Start or repeated Start detected.
1: Start or repeated Start detected.

Bit4:

STO: SMBus Stop Flag.
Write:
As a master, setting this bit to `1' causes a STOP condition to be transmitted after the next ACK
cycle. STO is cleared to `0' by hardware when the STOP is generated.
As a slave, software manages this bit when switching from Slave Receiver to Slave Transmitter
mode. See

Section 13.5.4

for details.

Read:
0: No Stop condition detected.
1: Stop condition detected (if in Slave Mode) or pending (if in Master Mode).

Bit3:

ACKRQ: SMBus Acknowledge Request.
This read-only bit is set to logic 1 when the SMBus has received a byte and needs the ACK bit to be
written with the correct ACK response value.

Bit2:

ARBLOST: SMBus Arbitration Lost Indicator.
This read-only bit is set to logic 1 when the SMBus loses arbitration while operating as a transmitter.
A lost arbitration while a slave indicates a bus error condition.

Bit1:

ACK: SMBus Acknowledge Flag.
This bit defines the out-going ACK level and records incoming ACK levels. It should be written each
time a byte is received (when ACKRQ=1), or read after each byte is transmitted.
0: A "not acknowledge" has been received (if in Transmitter Mode) OR will be transmitted (if in
Receiver Mode).
1: An "acknowledge" has been received (if in Transmitter Mode) OR will be transmitted (if in
Receiver Mode).

Bit0:

SI: SMBus Interrupt Flag.
This bit is set by hardware under the conditions listed in Table 13.3. SI must be cleared by software.
While SI is set, SCL is held low and the SMBus is stalled.

R/W

Reset Value

MASTER TXMODE

STA

STO

ACKRQ

ARBLOST

ACK

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

(bit addressable)

0xC0

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Table 13.3. Sources for Hardware Changes to SMB0CN

Bit

Set by Hardware When:

Cleared by Hardware When:

MASTER

· A START is generated.

· A STOP is generated.
· Arbitration is lost.

TXMODE

· START is generated.
· The SMBus interface enters transmitter mode

(after SMB0DAT is written before the start of an
SMBus frame).

· A START is detected.
· Arbitration is lost.
· SMB0DAT is not written before the start

of an SMBus frame.

STA

· A START followed by an address byte is received. · Must be cleared by software.

STO

· A STOP is detected while addressed as a slave.
· Arbitration is lost due to a detected STOP.

· A pending STOP is generated.

ACKRQ

· A byte has been received and an ACK response

value is needed.

· After each ACK cycle.

ARBLOST

· A repeated START is detected as a MASTER when

STA is low (unwanted repeated START).

· SCL is sensed low while attempting to generate a

STOP or repeated START condition.

· SDA is sensed low while transmitting a `1'

(excluding ACK bits).

· Each time SI is cleared.

ACK

· The incoming ACK value is low (ACKNOWL-

EDGE).

· The incoming ACK value is high (NOT

ACKNOWLEDGE).

· A START has been generated.
· Lost arbitration.
· A byte has been transmitted and an ACK/NACK

received.

· A byte has been received.
· A START or repeated START followed by a slave

address + R/W has been received.

· A STOP has been received.

· Must be cleared by software.

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13.4.3. Data Register

The SMBus Data register SMB0DAT holds a byte of serial data to be transmitted or one that has just been received.
Software may safely read or write to the data register when the SI flag is set. Software should not attempt to access
the SMB0DAT register when the SMBus is enabled and the SI flag is cleared to logic 0, as the interface may be in the
process of shifting a byte of data into or out of the register.

Data in SMB0DAT is always shifted out MSB first. After a byte has been received, the first bit of received data is
located at the MSB of SMB0DAT. While data is being shifted out, data on the bus is simultaneously being shifted in.
SMB0DAT always contains the last data byte present on the bus. In the event of lost arbitration, the transition from
master transmitter to slave receiver is made with the correct data or address in SMB0DAT.

Figure 13.7. SMB0DAT: SMBus Data Register

Bits7-0:

SMB0DAT: SMBus Data.
The SMB0DAT register contains a byte of data to be transmitted on the SMBus serial interface or a
byte that has just been received on the SMBus serial interface. The CPU can read from or write to this
register whenever the SI serial interrupt flag (SMB0CN.0) is set to logic one. The serial data in the
register remains stable as long as the SI flag is set. When the SI flag is not set, the system may be in
the process of shifting data in/out and the CPU should not attempt to access this register.

R/W

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xC2

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13.5.

SMBus Transfer Modes

The SMBus interface may be configured to operate as master and/or slave. At any particular time, it will be operating
in one of the following four modes: Master Transmitter, Master Receiver, Slave Transmitter, or Slave Receiver. The
SMBus interface enters Master Mode any time a START is generated, and remains in Master Mode until it loses arbi-
tration or generates a STOP. An SMBus interrupt is generated at the end of all SMBus byte frames; however, note that
the interrupt is generated before the ACK cycle when operating as a receiver, and after the ACK cycle when operating
as a transmitter.

13.5.1. Master Transmitter Mode

Serial data is transmitted on SDA while the serial clock is output on SCL. The SMBus interface generates the START
condition and transmits the first byte containing the address of the target slave and the data direction bit. In this case
the data direction bit (R/W) will be logic 0 (WRITE). The master then transmits one or more bytes of serial data.
After each byte is transmitted, an acknowledge bit is generated by the slave. The transfer is ended when the STO bit
is set and a STOP is generated. Note that the interface will switch to Master Receiver Mode if SMB0DAT is not writ-
ten following a Master Transmitter interrupt. Figure 13.8 shows a typical Master Transmitter sequence. Two transmit
data bytes are shown, though any number of bytes may be transmitted. Notice that the `data byte transferred' inter-
rupts occur after the ACK cycle in this mode.

Data Byte

SLA

S = START
P = STOP
A = ACK
W = WRITE
SLA = Slave Address

Received by SMBus
Interface

Transmitted by
SMBus Interface

Interrupt

Figure 13.8. Typical Master Transmitter Sequence

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13.5.2. Master Receiver Mode

Serial data is received on SDA while the serial clock is output on SCL. The SMBus interface generates the START
condition and transmits the first byte containing the address of the target slave and the data direction bit. In this case
the data direction bit (R/W) will be logic 1 (READ). Serial data is then received from the slave on SDA while the
SMBus outputs the serial clock. The slave transmits one or more bytes of serial data. After each byte is received,
ACKRQ is set to `1' and an interrupt is generated. Software must write the ACK bit (SMB0CN.1) to define the out-
going acknowledge value (Note: writing a `1' to the ACK bit generates an ACK; writing a `0' generates a NACK).
Software should write a `0' to the ACK bit after the last byte is received, to transmit a NACK. The interface exits
Master Receiver Mode after the STO bit is set and a STOP is generated. Note that the interface will switch to Master
Transmitter Mode if SMB0DAT is written while an active Master Receiver. Figure 13.9 shows a typical Master
Receiver sequence. Two received data bytes are shown, though any number of bytes may be received. Notice that the
`data byte transferred' interrupts occur before the ACK cycle in this mode.

Figure 13.9. Typical Master Receiver Sequence

Data Byte

SLA

S = START
P = STOP
A = ACK
N = NACK
R = READ
SLA = Slave Address

Received by SMBus
Interface

Transmitted by
SMBus Interface

Interrupt

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13.5.3. Slave Receiver Mode

Serial data is received on SDA and the clock is received on SCL. When slave events are enabled (INH = 0), the inter-
face enters Slave Receiver Mode when a START followed by a slave address and direction bit (WRITE in this case)
is received. Upon entering Slave Receiver Mode, an interrupt is generated and the ACKRQ bit is set. Software
responds to the received slave address with an ACK, or ignores the received slave address with a NACK. If the
received slave address is ignored, slave interrupts will be inhibited until the next START is detected. If the received
slave address is acknowledged, zero or more data bytes are received. Software must write the ACK bit after each
received byte to ACK or NACK the received byte. The interface exits Slave Receiver Mode after receiving a STOP.
Note that the interface will switch to Slave Transmitter Mode if SMB0DAT is written while an active Slave Receiver;
see

Section 13.5.4

for details on this procedure. Figure 13.10 shows a typical Slave Receiver sequence. Two received

data bytes are shown, though any number of bytes may be received. Notice that the `data byte transferred' interrupts
occur before the ACK cycle in this mode.

SLA

Data Byte

S = START
P = STOP
A = ACK
R = READ
SLA = Slave Address

Received by SMBus
Interface

Transmitted by
SMBus Interface

Interrupt

Figure 13.10. Typical Slave Receiver Sequence

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13.5.4. Slave Transmitter Mode

Serial data is transmitted on SDA and the clock is received on SCL. When slave events are enabled (INH = 0), the
interface enters Slave Receiver Mode (to receive the slave address) when a START followed by a slave address and
direction bit (READ in this case) is received. Software responds to the received slave address with an ACK, or
ignores the received slave address with a NACK. If the received address is ignored, slave interrupts will be inhibited
until the next START is detected. If the received slave address is acknowledged, software should write data to
SMB0DAT to force the SMBus into Slave Transmitter Mode. The switch from Slave Receiver to Slave Transmitter
requires software management. Software should perform the steps outlined below only when a valid slave address is
received (indicated by the label "RX-to-TX Steps" in Figure 13.11).

Step 1. Set ACK to `1'.
Step 2. Write outgoing data to SMB0DAT.
Step 3. Check SMB0DAT.7; if `1', do not perform steps 4, 6 or 7.
Step 4. Set STO to `1'.
Step 5. Clear SI to `0'.
Step 6. Poll for TXMODE => `1'.
Step 7. Clear STO to `0' (must be done before the next ACK cycle).

The interface enters Slave Transmitter Mode and transmits one or more bytes of data (the above steps are only
required before the first byte of the transfer). After each byte is transmitted, the master sends an acknowledge bit; if
the acknowledge bit is an ACK, SMB0DAT should be written with the next data byte. If the acknowledge bit is a
NACK, SMB0DAT should not be written to before SI is cleared (Note: an error condition may be generated if
SMB0DAT is written following a received NACK while in Slave Transmitter Mode). The interface exits Slave Trans-
mitter Mode after receiving a STOP. Note that the interface will switch to Slave Receiver Mode if SMB0DAT is not
written following a Slave Transmitter interrupt. Figure 13.11 shows a typical Slave Transmitter sequence. Two trans-
mitted data bytes are shown, though any number of bytes may be transmitted. Notice that the `data byte transferred'
interrupts occur after the ACK cycle in this mode.

SLA

Data Byte

S = START
P = STOP
N = NACK
W = WRITE
SLA = Slave Address

Received by SMBus
Interface

Transmitted by
SMBus Interface

Interrupt

Perform RX-to-TX
Steps Here

Figure 13.11. Typical Slave Transmitter Sequence

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13.6.

SMBus Status Decoding

The current SMBus status can be easily decoded using the SMB0CN register. In the table below, STATUS VECTOR
refers to the four upper bits of SMB0CN: MASTER, TXMODE, STA, and STO. Note that the shown response
options are only the typical responses; application-specific procedures are allowed as long as they conform with the
SMBus specification. Highlighted responses are allowed but do not conform to the SMBus specification.

Table 13.4. SMBus Status Decoding

VALUES READ

CURRENT SMBUS STATE

TYPICAL RESPONSE

OPTIONS

VALUES

WRITTEN

ACKRQ

ARB

ACK

RANSM

I
T

1110

X A master START was generated.

Load slave address + R/W into
SMB0DAT.

1100

A master data or address byte was
transmitted; NACK received.

Set STA to restart transfer.

Abort transfer.

A master data or address byte was
transmitted; ACK received.

Load next data byte into
SMB0DAT

End transfer with STOP

End transfer with STOP and
start another transfer.

Send repeated START

Switch to Master Receiver
Mode (clear SI without writing
new data to SMB0DAT).

I
V

1000

A master data byte was received;
ACK requested.

Acknowledge received byte;
Read SMB0DAT.

Send NACK to indicate last
byte, and send STOP.

Send NACK to indicate last
byte, and send STOP followed
by START.

Send ACK followed by
repeated START.

Send NACK to indicate last
byte, and send repeated START.

Send ACK and switch to Mas-
ter Transmitter Mode (write
to SMB0DAT before clearing
SI).

Send NACK and switch to
Master Transmitter Mode
(write to SMB0DAT before
clearing SI).

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AVE

IVE

0010

A slave address was received; ACK
requested.

Acknowledge received address
(received slave address match,
R/W bit = READ).

Do not acknowledge received
address.

Acknowledge received address,
and switch to transmitter mode
(received slave address match,
R/W bit = WRITE); see

Section

13.5.4

for procedure.

Lost arbitration as master; slave
address received; ACK requested.

Acknowledge received address
(received slave address match,
R/W bit = READ).

Do not acknowledge received
address.

Acknowledge received address,
and switch to transmitter mode
(received slave address match,
R/W bit = WRITE); see

Section

13.5.4

for procedure.

Reschedule failed transfer; do
not acknowledge received
address

0010

Lost arbitration while attempting a
repeated START.

Abort failed transfer.

Reschedule failed transfer.

0001

Lost arbitration while attempting a
STOP.

No action required (transfer
complete/aborted).

A STOP was detected while an
addressed slave receiver.

No action required (transfer
complete).

Lost arbitration due to a detected
STOP.

Abort transfer.

Reschedule failed transfer.

0000

A slave byte was received; ACK
requested.

Acknowledge received byte;
Read SMB0DAT.

Do not acknowledge received
byte.

Lost arbitration while transmitting a
data byte as master.

Abort failed transfer.

Reschedule failed transfer.

Table 13.4. SMBus Status Decoding

MOD

VALUES READ

CURRENT SMBUS STATE

TYPICAL RESPONSE

OPTIONS

VALUES

WRITTEN

ACKRQ

ARB

ACK

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14.

UART0

UART0 is an asynchronous, full duplex serial port offering modes 1 and 3 of the standard 8051 UART. Enhanced
baud rate support allows a wide range of clock sources to generate standard baud rates (details in

Section

"14.1. Enhanced Baud Rate Generation" on page 124

). Received data buffering allows UART0 to start reception

of a second incoming data byte before software has finished reading the previous data byte.

UART0 has two associated SFRs: Serial Control Register 0 (SCON0) and Serial Data Buffer 0 (SBUF0). The single
SBUF0 location provides access to both transmit and receive registers. Reading SBUF0 accesses the buffered
Receive register; writing SBUF0 accesses the Transmit register.

With UART0 interrupts enabled, an interrupt is generated each time a transmit is completed (TI0 is set in SCON0), or
a data byte has been received (RI0 is set in SCON0). The UART0 interrupt flags are not cleared by hardware when
the CPU vectors to the interrupt service routine. They must be cleared manually by software, allowing software to
determine the cause of the UART0 interrupt (transmit complete or receive complete).

Figure 14.1. UART0 Block Diagram

UART Baud

Rate Generator

SCON0

Tx Control

Tx Clock

Send

SBUF

(TX Shift)

Start

Data

Write to

SBUF

Crossbar

Shift

Zero Detector

Tx IRQ

SET

CLR

Stop Bit

TB8

SFR Bus

Serial

Port

Interrupt

Port I/O

Rx Control

Start

Rx Clock

Load

SBUF

Shift

0x1FF

RB8

Rx IRQ

Input Shift Register

(9 bits)

Load SBUF0

Read

SBUF

SFR Bus

Crossbar

SBUF

(RX Latch)

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14.1.

Enhanced Baud Rate Generation

The UART0 baud rate is generated by Timer 1 in 8-bit auto-reload mode. The TX clock is generated by TL1; the RX
clock is generated by a copy of TL1 (shown as RX Timer in Figure 14.2), which is not user-accessible. Both TX and
RX Timer overflows are divided by two to generate the TX and RX baud rates. The RX Timer runs when Timer 1 is
enabled, and uses the same reload value (TH1). However, an RX Timer reload is forced when a START condition is
detected on the RX pin. This allows a receive to begin any time a START is detected, independent of the TX Timer
state.

Timer 1 should be configured for Mode 2, 8-bit auto-reload (see

Section "15.1.3. Mode 2: 8-bit Counter/Timer

with Auto-Reload" on page 135

). The Timer 1 reload value should be set so that overflows will occur at two times

the desired UART baud rate frequency. Note that Timer 1 may be clocked by one of five sources: SYSCLK,
SYSCLK / 4, SYSCLK / 12, SYSCLK / 48, or the external oscillator clock / 8. For any given Timer 1 clock source,
the UART0 baud rate is determined by Equation 14.1.

Where T1

CLK

is the frequency of the clock supplied to Timer 1, and T1H is the high byte of Timer 1 (reload value).

Timer 1 clock frequency is selected as described in

Section "15.2. Timer 2" on page 141

. A quick reference for typ-

ical baud rates and system clock frequencies is given in Tables 14.1 through 14.6. Note that the internal oscillator
may still generate the system clock when the external oscillator is driving Timer 1 (see

Section "15.1. Timer 0 and

Timer 1" on page 133

for more details).

Figure 14.2. UART0 Baud Rate Logic

RX Timer

Start

Detected

Overflow

TH1

TL1

TX Clock

RX Clock

Timer 1

UART0

Equation 14.1. UART0 Baud Rate

UartBaudRate

CLK

256

T1H

(

)

-------------------------------

1
2

---

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14.2.

Operational Modes

UART0 provides standard asynchronous, full duplex communication. The UART mode (8-bit or 9-bit) is selected by
the S0MODE bit (SCON0.7). Typical UART connection options are shown below.

14.2.1. 8-Bit UART

8-Bit UART mode uses a total of 10 bits per data byte: one start bit, eight data bits (LSB first), and one stop bit. Data
are transmitted LSB first from the TX pin and received at the RX pin. On receive, the eight data bits are stored in
SBUF0 and the stop bit goes into RB80 (SCON0.2).

Data transmission begins when software writes a data byte to the SBUF0 register. The TI0 Transmit Interrupt Flag
(SCON0.1) is set at the end of the transmission (the beginning of the stop-bit time). Data reception can begin any
time after the REN0 Receive Enable bit (SCON0.4) is set to logic 1. After the stop bit is received, the data byte will
be loaded into the SBUF0 receive register if the following conditions are met: RI0 must be logic 0, and if MCE0 is
logic 1, the stop bit must be logic 1. In the event of a receive data overrun, the first received 8 bits are latched into the
SBUF0 receive register and the following overrun data bits are lost.

If these conditions are met, the eight bits of data is stored in SBUF0, the stop bit is stored in RB80 and the RI0 flag is
set. If these conditions are not met, SBUF0 and RB80 will not be loaded and the RI0 flag will not be set. An interrupt
will occur if enabled when either TI0 or RI0 is set.

Figure 14.3. UART Interconnect Diagram

RS-232

C8051Fxxx

RS-232

LEVEL

XLTR

C8051Fxxx

MCU

Figure 14.4. 8-Bit UART Timing Diagram

START

BIT

MARK

STOP

BIT

BIT TIMES

BIT SAMPLING

SPACE

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14.2.2. 9-Bit UART

9-bit UART mode uses a total of eleven bits per data byte: a start bit, 8 data bits (LSB first), a programmable ninth
data bit, and a stop bit. The state of the ninth transmit data bit is determined by the value in TB80 (SCON0.3), which
is assigned by user software. It can be assigned the value of the parity flag (bit P in register PSW) for error detection,
or used in multiprocessor communications. On receive, the ninth data bit goes into RB80 (SCON0.2) and the stop bit
is ignored.

Data transmission begins when an instruction writes a data byte to the SBUF0 register. The TI0 Transmit Interrupt
Flag (SCON0.1) is set at the end of the transmission (the beginning of the stop-bit time). Data reception can begin
any time after the REN0 Receive Enable bit (SCON0.4) is set to `1'. After the stop bit is received, the data byte will
be loaded into the SBUF0 receive register if the following conditions are met: (1) RI0 must be logic 0, and (2) if
MCE0 is logic 1, the 9th bit must be logic 1 (when MCE0 is logic 0, the state of the ninth data bit is unimportant). If
these conditions are met, the eight bits of data are stored in SBUF0, the ninth bit is stored in RB80, and the RI0 flag is
set to `1'. If the above conditions are not met, SBUF0 and RB80 will not be loaded and the RI0 flag will not be set to
`1'. A UART0 interrupt will occur if enabled when either TI0 or RI0 is set to `1'.

Figure 14.5. 9-Bit UART Timing Diagram

START

BIT

MARK

STOP

BIT

BIT TIMES

BIT SAMPLING

SPACE

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14.3.

Multiprocessor Communications

9-Bit UART mode supports multiprocessor communication between a master processor and one or more slave pro-
cessors by special use of the ninth data bit. When a master processor wants to transmit to one or more slaves, it first
sends an address byte to select the target(s). An address byte differs from a data byte in that its ninth bit is logic 1; in
a data byte, the ninth bit is always set to logic 0.

Setting the MCE0 bit (SCON.5) of a slave processor configures its UART such that when a stop bit is received, the
UART will generate an interrupt only if the ninth bit is logic one (RB80 = 1) signifying an address byte has been
received. In the UART interrupt handler, software will compare the received address with the slave's own assigned 8-
bit address. If the addresses match, the slave will clear its MCE0 bit to enable interrupts on the reception of the fol-
lowing data byte(s). Slaves that weren't addressed leave their MCE0 bits set and do not generate interrupts on the
reception of the following data bytes, thereby ignoring the data. Once the entire message is received, the addressed
slave resets its MCE0 bit to ignore all transmissions until it receives the next address byte.

Multiple addresses can be assigned to a single slave and/or a single address can be assigned to multiple slaves,
thereby enabling "broadcast" transmissions to more than one slave simultaneously. The master processor can be con-
figured to receive all transmissions or a protocol can be implemented such that the master/slave role is temporarily
reversed to enable half-duplex transmission between the original master and slave(s).

Figure 14.6. UART Multi-Processor Mode Interconnect Diagram

Master
Device

Slave

Device

Slave

Device

Slave

Device

+5V

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Figure 14.7. SCON0: Serial Port 0 Control Register

Bit7:

S0MODE: Serial Port 0 Operation Mode.
This bit selects the UART0 Operation Mode.
0: Mode 0: 8-bit UART with Variable Baud Rate
1: Mode 1: 9-bit UART with Variable Baud Rate

Bit6:

UNUSED. Read = 1b. Write = don't care.

Bit5:

MCE0: Multiprocessor Communication Enable.
The function of this bit is dependent on the Serial Port 0 Operation Mode.
Mode 0: Checks for valid stop bit.

0: Logic level of stop bit is ignored.
1: RI0 will only be activated if stop bit is logic level 1.

Mode 1: Multiprocessor Communications Enable.

0: Logic level of ninth bit is ignored.
1: RI0 is set and an interrupt is generated only when the ninth bit is logic 1.

Bit4:

REN0: Receive Enable.
This bit enables/disables the UART receiver.
0: UART0 reception disabled.
1: UART0 reception enabled.

Bit3:

TB80: Ninth Transmission Bit.
The logic level of this bit will be assigned to the ninth transmission bit in 9-bit UART Mode. It is not
used in 8-bit UART Mode. Set or cleared by software as required.

Bit2:

RB80: Ninth Receive Bit.
RB80 is assigned the value of the STOP bit in Mode 0; it is assigned the value of the 9th data bit in
Mode 1.

Bit1:

TI0: Transmit Interrupt Flag.
Set by hardware when a byte of data has been transmitted by UART0 (after the 8th bit in 8-bit UART
Mode, or at the beginning of the STOP bit in 9-bit UART Mode). When the UART0 interrupt is
enabled, setting this bit causes the CPU to vector to the UART0 interrupt service routine. This bit
must be cleared manually by software

Bit0:

RI0: Receive Interrupt Flag.
Set to `1' by hardware when a byte of data has been received by UART0 (set at the STOP bit sam-
pling time). When the UART0 interrupt is enabled, setting this bit to `1' causes the CPU to vector to
the UART0 interrupt service routine. This bit must be cleared manually by software.

R/W

Reset Value

S0MODE

MCE0

REN0

TB80

RB80

TI0

RI0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

(bit addressable)

0x98

Page 130

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C8051F304/5

Table 14.1. Timer Settings for Standard Baud Rates Using The Internal Oscillator

Frequency: 24.5 MHz

Target
Baud Rate
(bps)

Baud Rate
% Error

Oscillator

Divide
Factor

Timer Clock
Source

SCA1-SCA0

(pre-scale select)

T1M

Timer 1
Reload
Value (hex)

SYS

f
r
om

ternal

230400

-0.32%

106

SYSCLK

0xCB

115200

-0.32%

212

SYSCLK

0x96

57600

0.15%

426

SYSCLK

0x2B

28800

-0.32%

848

SYSCLK / 4

0x96

14400

0.15%

1704

SYSCLK / 12

0xB9

9600

-0.32%

2544

SYSCLK / 12

0x96

2400

-0.32%

10176

SYSCLK / 48

0x96

1200

0.15%

20448

SYSCLK / 48

0x2B

X = Don't care

SCA1-SCA0 and T1M bit definitions can be found in

Section 15.1

Table 14.2. Timer Settings for Standard Baud Rates Using an External Oscillator

Frequency: 25.0 MHz

Target
Baud Rate
(bps)

Baud Rate
% Error

Oscillator

Divide
Factor

Timer Clock
Source

SCA1-SCA0

(pre-scale select)

T1M

Timer 1
Reload
Value (hex)

SCL

f
r
om

Extern

s
c.

230400

-0.47%

108

SYSCLK

0xCA

115200

0.45%

218

SYSCLK

0x93

57600

-0.01%

434

SYSCLK

0x27

28800

0.45%

872

SYSCLK / 4

0x93

14400

-0.01%

1736

SYSCLK / 4

0x27

9600

0.15%

2608

EXTCLK / 8

0x5D

2400

0.45%

10464

SYSCLK / 48

0x93

1200

-0.01%

20832

SYSCLK / 48

0x27

f
r
om

Inter

57600

-0.47%

432

EXTCLK / 8

0xE5

28800

-0.47%

864

EXTCLK / 8

0xCA

14400

0.45%

1744

EXTCLK / 8

0x93

9600

0.15%

2608

EXTCLK / 8

0x5D

X = Don't care

SCA1-SCA0 and T1M bit definitions can be found in

Section 15.1

DS004-2.2 APR 03

Page 131

PRELIMINARY

C8051F300/1/2/3

C8051F304/5

Table 14.3. Timer Settings for Standard Baud Rates Using an External Oscillator

Frequency: 22.1184 MHz

Target
Baud Rate
(bps)

Baud Rate
% Error

Oscillator

Divide
Factor

Timer Clock
Source

SCA1-SCA0

(pre-scale select)

T1M

Timer 1
Reload
Value (hex)

SYS

f
r
om

Extern

s
c.

230400

0.00%

SYSCLK

0xD0

115200

0.00%

192

SYSCLK

0xA0

57600

0.00%

384

SYSCLK

0x40

28800

0.00%

768

SYSCLK / 12

0xE0

14400

0.00%

1536

SYSCLK / 12

0xC0

9600

0.00%

2304

SYSCLK / 12

0xA0

2400

0.00%

9216

SYSCLK / 48

0xA0

1200

0.00%

18432

SYSCLK / 48

0x40

SYSC

f
r
o

I
n

tern

s
c.

230400

0.00%

EXTCLK / 8

0xFA

115200

0.00%

192

EXTCLK / 8

0xF4

57600

0.00%

384

EXTCLK / 8

0xE8

28800

0.00%

768

EXTCLK / 8

0xD0

14400

0.00%

1536

EXTCLK / 8

0xA0

9600

0.00%

2304

EXTCLK / 8

0x70

X = Don't care

SCA1-SCA0 and T1M bit definitions can be found in

Section 15.1

Table 14.4. Timer Settings for Standard Baud Rates Using an External Oscillator

Frequency: 18.432 MHz

Target
Baud Rate
(bps)

Baud Rate
% Error

Oscillator

Divide
Factor

Timer Clock
Source

SCA1-SCA0

(pre-scale select)

T1M

Timer 1
Reload
Value (hex)

SYS

f
r
om

Extern

s
c.

230400

0.00%

SYSCLK

0xD8

115200

0.00%

160

SYSCLK

0xB0

57600

0.00%

320

SYSCLK

0x60

28800

0.00%

640

SYSCLK / 4

0xB0

14400

0.00%

1280

SYSCLK / 4

0x60

9600

0.00%

1920

SYSCLK / 12

0xB0

2400

0.00%

7680

SYSCLK / 48

0xB0

1200

0.00%

15360

SYSCLK / 48

0x60

SYSC

f
r
o

t
e
r
n

s
c
.

230400

0.00%

EXTCLK / 8

0xFB

115200

0.00%

160

EXTCLK / 8

0xF6

57600

0.00%

320

EXTCLK / 8

0xEC

28800

0.00%

640

EXTCLK / 8

0xD8

14400

0.00%

1280

EXTCLK / 8

0xB0

9600

0.00%

1920

EXTCLK / 8

0x88

X = Don't care

SCA1-SCA0 and T1M bit definitions can be found in

Section 15.1

Page 132

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Table 14.5. Timer Settings for Standard Baud Rates Using an External Oscillator

Frequency: 11.0592 MHz

Target
Baud Rate
(bps)

Baud Rate
% Error

Oscillator

Divide
Factor

Timer Clock
Source

SCA1-SCA0

(pre-scale select)

T1M

Timer 1
Reload
Value (hex)

SYS

f
r
om

Extern

s
c.

230400

0.00%

SYSCLK

0xE8

115200

0.00%

SYSCLK

0xD0

57600

0.00%

192

SYSCLK

0xA0

28800

0.00%

384

SYSCLK

0x40

14400

0.00%

768

SYSCLK / 12

0xE0

9600

0.00%

1152

SYSCLK / 12

0xD0

2400

0.00%

4608

SYSCLK / 12

0x40

1200

0.00%

9216

SYSCLK / 48

0xA0

SYSC

f
r
o

I
n

tern

s
c.

230400

0.00%

EXTCLK / 8

0xFD

115200

0.00%

EXTCLK / 8

0xFA

57600

0.00%

192

EXTCLK / 8

0xF4

28800

0.00%

384

EXTCLK / 8

0xE8

14400

0.00%

768

EXTCLK / 8

0xD0

9600

0.00%

1152

EXTCLK / 8

0xB8

X = Don't care

SCA1-SCA0 and T1M bit definitions can be found in

Section 15.1

Table 14.6. Timer Settings for Standard Baud Rates Using an External Oscillator

Frequency: 3.6864 MHz

Target
Baud Rate
(bps)

Baud Rate
% Error

Oscillator

Divide
Factor

Timer Clock
Source

SCA1-SCA0

(pre-scale select)

T1M

Timer 1
Reload
Value (hex)

SYS

f
r
om

Extern

s
c.

230400

0.00%

SYSCLK

0xF8

115200

0.00%

SYSCLK

0xF0

57600

0.00%

SYSCLK

0xE0

28800

0.00%

128

SYSCLK

0xC0

14400

0.00%

256

SYSCLK

0x80

9600

0.00%

384

SYSCLK

0x40

2400

0.00%

1536

SYSCLK / 12

0xC0

1200

0.00%

3072

SYSCLK / 12

0x80

SYSC

f
r
o

t
e
r
n

s
c
.

230400

0.00%

EXTCLK / 8

0xFF

115200

0.00%

EXTCLK / 8

0xFE

57600

0.00%

EXTCLK / 8

0xFC

28800

0.00%

128

EXTCLK / 8

0xF8

14400

0.00%

256

EXTCLK / 8

0xF0

9600

0.00%

384

EXTCLK / 8

0xE8

X = Don't care

SCA1-SCA0 and T1M bit definitions can be found in

Section 15.1

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15.

TIMERS

Each MCU includes 3 counter/timers: two are 16-bit counter/timers compatible with those found in the standard
8051, and one is a 16-bit auto-reload timer for use with the ADC, SMBus, or for general purpose use. These timers
can be used to measure time intervals, count external events and generate periodic interrupt requests. Timer 0 and
Timer 1 are nearly identical and have four primary modes of operation. Timer 2 offers 16-bit and split 8-bit timer
functionality with auto-reload.

Timers 0 and 1 may be clocked by one of five sources, determined by the Timer Mode Select bits (T1M-T0M) and
the Clock Scale bits (SCA1-SCA0). The Clock Scale bits define a pre-scaled clock from which Timer 0 and/or
Timer 1 may be clocked (See Figure 15.6 for pre-scaled clock selection).

Timer 0/1 may then be configured to use this pre-scaled clock signal or the system clock. Timer 2 may be clocked by
the system clock, the system clock divided by 12, or the external oscillator clock source divided by 8.

Timer 0 and Timer 1 may also be operated as counters. When functioning as a counter, a counter/timer register is
incremented on each high-to-low transition at the selected input pin. Events with a frequency of up to one-fourth the
system clock's frequency can be counted. The input signal need not be periodic, but it should be held at a given level
for at least two full system clock cycles to ensure the level is properly sampled.

15.1.

Timer 0 and Timer 1

Each timer is implemented as 16-bit register accessed as two separate bytes: a low byte (TL0 or TL1) and a high byte
(TH0 or TH1). The Counter/Timer Control register (TCON) is used to enable Timer 0 and Timer 1 as well as indicate
their status. Timer 0 interrupts can be enabled by setting the ET0 bit in the IE regitser (

Section "8.3.5. Interrupt

Register Descriptions" on page 70

); Timer 1 interrupts can be enabled by setting the ET1 bit in the IE register (

Sec-

tion 8.3.5

). Both counter/timers operate in one of four primary modes selected by setting the Mode Select bits T1M1-

T0M0 in the Counter/Timer Mode register (TMOD). Each timer can be configured independently. Each operating
mode is described below.

15.1.1. Mode 0: 13-bit Counter/Timer

Timer 0 and Timer 1 operate as 13-bit counter/timers in Mode 0. The following describes the configuration and oper-
ation of Timer 0. However, both timers operate identically, and Timer 1 is configured in the same manner as
described for Timer 0.

The TH0 register holds the eight MSBs of the 13-bit counter/timer. TL0 holds the five LSBs in bit positions TL0.4-
TL0.0. The three upper bits of TL0 (TL0.7-TL0.5) are indeterminate and should be masked out or ignored when read-
ing. As the 13-bit timer register increments and overflows from 0x1FFF (all ones) to 0x0000, the timer overflow flag
TF0 (TCON.5) is set and an interrupt will occur if Timer 0 interrupts are enabled.

The C/T0 bit (TMOD.2) selects the counter/timer's clock source. When C/T0 is set to logic 1, high-to-low transitions
at the selected Timer 0 input pin (T0) increment the timer register (Refer to

Section "12.1. Priority Crossbar

Decoder" on page 96

for information on selecting and configuring external I/O pins). Clearing C/T selects the clock

defined by the T0M bit (CKCON.3). When T0M is set, Timer 0 is clocked by the system clock. When T0M is
cleared, Timer 0 is clocked by the source selected by the Clock Scale bits in CKCON (see Figure 15.6).

Timer 0 and Timer 1 Modes:

Timer 2 Modes:

13-bit counter/timer

16-bit timer with auto-reload

16-bit counter/timer

8-bit counter/timer with auto-reload

Two 8-bit timers with auto-reload

Two 8-bit counter/timers (Timer 0 only)

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Setting the TR0 bit (TCON.4) enables the timer when either GATE0 (TMOD.3) is logic 0 or the input signal /INT0 is
active as defined by bit IN0PL in register INT01CF (see Figure 8.14). Setting GATE0 to `1' allows the timer to be
controlled by the external input signal /INT0 (see

Section "8.3.5. Interrupt Register Descriptions" on page 70

facilitating pulse width measurements.

Setting TR0 does not force the timer to reset. The timer registers should be loaded with the desired initial value before
the timer is enabled.

TL1 and TH1 form the 13-bit register for Timer 1 in the same manner as described above for TL0 and TH0. Timer 1
is configured and controlled using the relevant TCON and TMOD bits just as with Timer 0. The input signal /INT1 is
used with Timer 1; the /INT1 polarity is defined by bit IN1PL in register INT01CF (see Figure 8.14).

15.1.2. Mode 1: 16-bit Counter/Timer

Mode 1 operation is the same as Mode 0, except that the counter/timer registers use all 16 bits. The counter/timers are
enabled and configured in Mode 1 in the same manner as for Mode 0.

TR0

GATE0

/INT0

Counter/Timer

Disabled

Enabled

Disabled

Enabled

X = Don't Care

Figure 15.1. T0 Mode 0 Block Diagram

TCLK

TL0

(5 bits)

TH0

(8 bits)

TF0

TR0

TR1

TF1

IE1
IT1
IE0
IT0

Interrupt

TR0

SYSCLK

Pre-scaled Clock

CKCON

T
2

S
C
A

T
2

T
1

T
0

TMOD

T
1

G
A

T
E
1

G
A

T
E
0

T
0

GATE0

/INT0

Crossbar

INT01CF

L
1

L
0

L
2

L
1

L
0

IN0PL

XOR

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15.1.3. Mode 2: 8-bit Counter/Timer with Auto-Reload

Mode 2 configures Timer 0 and Timer 1 to operate as 8-bit counter/timers with automatic reload of the start value.
TL0 holds the count and TH0 holds the reload value. When the counter in TL0 overflows from all ones to 0x00, the
timer overflow flag TF0 (TCON.5) is set and the counter in TL0 is reloaded from TH0. If Timer 0 interrupts are
enabled, an interrupt will occur when the TF0 flag is set. The reload value in TH0 is not changed. TL0 must be initial-
ized to the desired value before enabling the timer for the first count to be correct. When in Mode 2, Timer 1 operates
identically to Timer 0.

Both counter/timers are enabled and configured in Mode 2 in the same manner as Mode 0. Setting the TR0 bit
(TCON.4) enables the timer when either GATE0 (TMOD.3) is logic 0 or when the input signal /INT0 is active as
defined by bit IN0PL in register INT01CF (see

Section "8.3.2. External Interrupts" on page 68

for details on the

external input signals /INT0 and /INT1).

Figure 15.2. T0 Mode 2 Block Diagram

TCLK

TMOD

T
1

A
T
E

T
0

TCON

TF0

TR0

TR1

TF1

IE1
IT1
IE0
IT0

Interrupt

TL0

(8 bits)

Reload

TH0

(8 bits)

SYSCLK

Pre-scaled Clock

CKCON

T
2

M
H

S
C
A

T
2

T
1

T
0

INT01CF

L
1

L
0

L
2

L
1

L
0

TR0

GATE0

IN0PL

XOR

/INT0

Crossbar

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15.1.4. Mode 3: Two 8-bit Counter/Timers (Timer 0 Only)

In Mode 3, Timer 0 is configured as two separate 8-bit counter/timers held in TL0 and TH0. The counter/timer in TL0
is controlled using the Timer 0 control/status bits in TCON and TMOD: TR0, C/T0, GATE0 and TF0. TL0 can use
either the system clock or an external input signal as its timebase. The TH0 register is restricted to a timer function
sourced by the system clock or prescaled clock. TH0 is enabled using the Timer 1 run control bit TR1. TH0 sets the
Timer 1 overflow flag TF1 on overflow and thus controls the Timer 1 interrupt.

Timer 1 is inactive in Mode 3. When Timer 0 is operating in Mode 3, Timer 1 can be operated in Modes 0, 1 or 2, but
cannot be clocked by external signals nor set the TF1 flag and generate an interrupt. However, the Timer 1 overflow
can be used to generate baud rates for the SMBus and/or UART, and/or initiate ADC conversions. While Timer 0 is
operating in Mode 3, Timer 1 run control is handled through its mode settings. To run Timer 1 while Timer 0 is in
Mode 3, set the Timer 1 Mode as 0, 1, or 2. To disable Timer 1, configure it for Mode 3.

Figure 15.3. T0 Mode 3 Block Diagram

TL0

(8 bits)

TMOD

TF0

TR0

TR1

TF1

IE1
IT1
IE0
IT0

Interrupt

SYSCLK

Pre-scaled Clock

TR1

TH0

(8 bits)

CKCON

T
2

M
H

S
C
A

T
2

T
1

T
0

T
1

A
T
E

T
0

TR0

GATE0

IN0PL

XOR

/INT0

Crossbar

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Figure 15.4. TCON: Timer Control Register

Bit7:

TF1: Timer 1 Overflow Flag.
Set by hardware when Timer 1 overflows. This flag can be cleared by software but is automatically
cleared when the CPU vectors to the Timer 1 interrupt service routine.
0: No Timer 1 overflow detected.
1: Timer 1 has overflowed.

Bit6:

TR1: Timer 1 Run Control.
0: Timer 1 disabled.
1: Timer 1 enabled.

Bit5:

TF0: Timer 0 Overflow Flag.
Set by hardware when Timer 0 overflows. This flag can be cleared by software but is automatically
cleared when the CPU vectors to the Timer 0 interrupt service routine.
0: No Timer 0 overflow detected.
1: Timer 0 has overflowed.

Bit4:

TR0: Timer 0 Run Control.
0: Timer 0 disabled.
1: Timer 0 enabled.

Bit3:

IE1: External Interrupt 1.
This flag is set by hardware when an edge/level of type defined by IT1 is detected. It can be cleared
by software but is automatically cleared when the CPU vectors to the External Interrupt 1 service
routine if IT1 = 1. When IT1 = 0, this flag is set to `1' when /INT1 is active as defined by bit IN1PL
in register INT01CF (see Figure 8.14).

Bit2:

IT1: Interrupt 1 Type Select.
This bit selects whether the configured /INT1 interrupt will be edge or level sensitive. /INT1 is con-
figured active low or high by the IN1PL bit in the IT01CF register (see Figure 8.14).
0: /INT1 is level triggered.
1: /INT1 is edge triggered.

Bit1:

IE0: External Interrupt 0.
This flag is set by hardware when an edge/level of type defined by IT0 is detected. It can be cleared
by software but is automatically cleared when the CPU vectors to the External Interrupt 0 service
routine if IT0 = 1. When IT0 = 0, this flag is set to `1' when /INT0 is active as defined by bit IN0PL
in register INT01CF (see Figure 8.14).

Bit0:

IT0: Interrupt 0 Type Select.
This bit selects whether the configured /INT0 interrupt will be edge or level sensitive. /INT0 is con-
figured active low or high by the IN0PL bit in register IT01CF (see Figure 8.14).
0: /INT0 is level triggered.
1: /INT0 is edge triggered.

R/W

Reset Value

TF1

TR1

TF0

TR0

IE1

IT1

IE0

IT0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

(bit addressable)

0x88

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Figure 15.5. TMOD: Timer Mode Register

Bit7:

GATE1: Timer 1 Gate Control.
0: Timer 1 enabled when TR1 = 1 irrespective of /INT1 logic level.
1: Timer 1 enabled only when TR1 = 1 AND /INT1 is active as defined by bit IN1PL in register
INT01CF (see Figure 8.14).

Bit6:

C/T1: Counter/Timer 1 Select.
0: Timer Function: Timer 1 incremented by clock defined by T1M bit (CKCON.4).
1: Counter Function: Timer 1 incremented by high-to-low transitions on external input pin (T1).

Bits5-4:

T1M1-T1M0: Timer 1 Mode Select.
These bits select the Timer 1 operation mode.

Bit3:

GATE0: Timer 0 Gate Control.
0: Timer 0 enabled when TR0 = 1 irrespective of /INT0 logic level.
1: Timer 0 enabled only when TR0 = 1 AND /INT0 is active as defined by bit IN0PL in register
INT01CF (see Figure 8.14).

Bit2:

C/T0: Counter/Timer Select.
0: Timer Function: Timer 0 incremented by clock defined by T0M bit (CKCON.3).
1: Counter Function: Timer 0 incremented by high-to-low transitions on external input pin (T0).

Bits1-0:

T0M1-T0M0: Timer 0 Mode Select.
These bits select the Timer 0 operation mode.

R/W

Reset Value

GATE1

C/T1

T1M1

T1M0

GATE0

C/T0

T0M1

T0M0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0x89

T1M1

T1M0

Mode

Mode 0: 13-bit counter/timer

Mode 1: 16-bit counter/timer

Mode 2: 8-bit counter/timer with auto-reload

Mode 3: Timer 1 inactive

T0M1

T0M0

Mode

Mode 0: 13-bit counter/timer

Mode 1: 16-bit counter/timer

Mode 2: 8-bit counter/timer with auto-reload

Mode 3: Two 8-bit counter/timers

DS004-2.2 APR 03

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C8051F304/5

Figure 15.6. CKCON: Clock Control Register

Bit7:

UNUSED. Read = 0b, Write = don't care.

Bit6:

T2MH: Timer 2 High Byte Clock Select
This bit selects the clock supplied to the Timer 2 high byte if Timer 2 is configured in split 8-bit timer
mode. T2MH is ignored if Timer 2 is in any other mode.
0: Timer 2 high byte uses the clock defined by the T2XCLK bit in TMR2CN.
1: Timer 2 high byte uses the system clock.

Bit5:

T2ML: Timer 2 Low Byte Clock Select
This bit selects the clock supplied to Timer 2. If Timer 2 is configured in split 8-bit timer mode, this
bit selects the clock supplied to the lower 8-bit timer.
0: Timer 2 low byte uses the clock defined by the T2XCLK bit in TMR2CN.
1: Timer 2 low byte uses the system clock.

Bit4:

T1M: Timer 1 Clock Select.
This select the clock source supplied to Timer 1. T1M is ignored when C/T1 is set to logic 1.
0: Timer 1 uses the clock defined by the prescale bits, SCA1-SCA0.
1: Timer 1 uses the system clock.

Bit3:

T0M: Timer 0 Clock Select.
This bit selects the clock source supplied to Timer 0. T0M is ignored when C/T0 is set to logic 1.
0: Counter/Timer 0 uses the clock defined by the prescale bits, SCA1-SCA0.
1: Counter/Timer 0 uses the system clock.

Bit2:

UNUSED. Read = 0b, Write = don't care.

Bits1-0:

SCA1-SCA0: Timer 0/1 Prescale Bits
These bits control the division of the clock supplied to Timer 0 and/or Timer 1 if configured to use
prescaled clock inputs.

R/W

Reset Value

T2MH

T2ML

T1M

T0M

SCA1

SCA0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0x8E

SCA1

SCA0

Prescaled Clock

System clock divided by 12

System clock divided by 4

System clock divided by 48

External clock divided by 8

Note: External clock divided by 8 is synchronized with the
system clock, and the external clock must be less than or
equal to the system clock to operate in this mode.

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15.2.

Timer 2

Timer 2 is a 16-bit timer formed by two 8-bit SFRs: TMR2L (low byte) and TMR2H (high byte). Timer 2 may oper-
ate in 16-bit auto-reload mode or (split) 8-bit auto-reload mode. The T2SPLIT bit (TMR2CN.3) defines the Timer 2
operation mode.

Timer 2 may be clocked by the system clock, the system clock divided by 12, or the external oscillator source divided
by 8. The external clock mode is ideal for real-time clock (RTC) functionality, where the internal oscillator drives the
system clock while Timer 2 (and/or the PCA) is clocked by an external precison oscillator. Note that the external
oscillator source divided by 8 is synchronized with the system clock.

15.2.1. 16-bit Timer with Auto-Reload

When T2SPLIT (TMR2CN.3) is zero, Timer 2 operates as a 16-bit timer with auto-reload. Timer 2 can be clocked by
SYSCLK, SYSCLK divided by 12, or the external oscillator clock source divided by 8. As the 16-bit timer register
increments and overflows from 0xFFFF to 0x0000, the 16-bit value in the Timer 2 reload registers (TMR2RLH and
TMR2RLL) is loaded into the Timer 2 register as shown in Figure 15.11, and the Timer 2 High Byte Overflow Flag
(TMR2CN.7) is set. If Timer 2 interrupts are enabled (if IE.5 is set), an interrupt will be generated on each Timer 2
overflow. Additionally, if Timer 2 interrupts are enabled and the TF2LEN bit is set (TMR2CN.5), an interrupt will be
generated each time the lower 8 bits (TL2) overflow from 0xFF to 0x00.

Figure 15.11. Timer 2 16-Bit Mode Block Diagram

External Clock / 8

SYSCLK / 12

SYSCLK

TMR2L

TMR2H

TMR2RLL TMR2RLH

Reload

TCLK

TR2

T2SPLIT

TF2L

TF2H

T2XCLK

TR2

T2XCLK

CKCON

T
2

M
H

S
C
A
0

S
C
A
1

T
2

T
1

T
0

Interrupt

TF2LEN

To ADC,

SMBus

To SMBus

TMR2L

Overflow

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15.2.2. 8-bit Timers with Auto-Reload

When T2SPLIT is set, Timer 2 operates as two 8-bit timers (TMR2H and TMR2L). Both 8-bit timers operate in auto-
reload mode as shown in Figure 15.12. TMR2RLL holds the reload value for TMR2L; TMR2RLH holds the reload
value for TMR2H. The TR2 bit in TMR2CN handles the run control for TMR2H. TMR2L is always running when
configured for 8-bit Mode.

Each 8-bit timer may be configured to use SYSCLK, SYSCLK divided by 12, or the external oscillator clock source
divided by 8. The Timer 2 Clock Select bits (T2MH and T2ML in CKCON) select either SYSCLK or the clock
defined by the Timer 2 External Clock Select bit (T2XCLK in TMR2CN), as follows:

Note: External clock divided by 8 is synchronized with the system clock, and the external clock must be less than or
equal to the system clock to operate in this mode.

The TF2H bit is set when TMR2H overflows from 0xFF to 0x00; the TF2L bit is set when TMR2L overflows from
0xFF to 0x00. When Timer 2 interrupts are enabled (IE.5), an interrupt is generated each time TMR2H overflows. If
Timer 2 interrupts are enabled and TF2LEN (TMR2CN.5) is set, an interrupt is generated each time either TMR2L or
TMR2H overflows. When TF2LEN is enabled, software must check the TF2H and TF2L flags to determine the
source of the Timer 2 interrupt. The TF2H and TF2L interrupt flags are not cleared by hardware and must be manu-
ally cleared by software.

T2MH

T2XCLK

TH2 Clock Source

T2ML

T2XCLK

TL2 Clock Source

SYSCLK / 12

External Clock / 8

SYSCLK

Figure 15.12. Timer 2 8-Bit Mode Block Diagram

SYSCLK

TCLK

TR2

External Clock / 8

SYSCLK / 12

T2XCLK

TMR2H

TMR2RLH

Reload

CKCON

T
2

M
H

S
C
A

T
2

T
1

T
0

Reload

TCLK

TMR2L

TMR2RLL

Interrupt

R2CN

T2SPLIT

TF2LEN

TF2L

TF2H

T2XCLK

TR2

To ADC,

SMBus

To SMBus

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Bit7:

TF2H: Timer 2 High Byte Overflow Flag
Set by hardware when the Timer 2 high byte overflows from 0xFF to 0x00. In 16 bit mode, this will
occur when Timer 2 overflows from 0xFFFF to 0x0000. When the Timer 2 interrupt is enabled, set-
ting this bit causes the CPU to vector to the Timer 2 interrupt service routine. TF2H is not automati-
cally cleared by hardware and must be cleared by software.

Bit6:

TF2L: Timer 2 Low Byte Overflow Flag
Set by hardware when the Timer 2 low byte overflows from 0xFF to 0x00. When this bit is set, an
interrupt will be generated if TF2LEN is set and Timer 2 interrupts are enabled. TF2L will set when
the low byte overflows regardless of the Timer 2 mode. This bit is not automatically cleared by hard-
ware.

Bit5:

TF2LEN: Timer 2 Low Byte Interrupt Enable.
This bit enables/disables Timer 2 Low Byte interrupts. If TF2LEN is set and Timer 2 interrupts are
enabled, an interrupt will be generated when the low byte of Timer 2 overflows. This bit should be
cleared when operating Timer 2 in 16-bit mode.
0: Timer 2 Low Byte interrupts disabled.
1: Timer 2 Low Byte interrupts enabled.

Bit4:

UNUSED. Read = 0b. Write = don't care.

Bit3:

T2SPLIT: Timer 2 Split Mode Enable
When this bit is set, Timer 2 operates as two 8-bit timers with auto-reload.
0: Timer 2 operates in 16-bit auto-reload mode.
1: Timer 2 operates as two 8-bit auto-reload timers.

Bit2:

TR2: Timer 2 Run Control.
This bit enables/disables Timer 2. In 8-bit mode, this bit enables/disables TH2 only; TL2 is always
enabled in this mode.
0: Timer 2 disabled.
1: Timer 2 enabled.

Bit1:

UNUSED. Read = 0b. Write = don't care.

Bit0:

T2XCLK: Timer 2 External Clock Select
This bit selects the external clock source for Timer 2. If Timer 2 is in 8-bit mode, this bit selects the
external oscillator clock source for both timer bytes. However, the Timer 2 Clock Select bits (T2MH
and T2ML in register CKCON) may still be used to select between the external clock and the system
clock for either timer.
0: Timer 2 external clock selection is the system clock divided by 12.
1: Timer 2 external clock selection is the external clock divided by 8. Note that the external oscillator
source divided by 8 is synchronized with the system clock.

R/W

Reset Value

TF2H

TF2L

TF2LEN

T2SPLIT

TR2

T2XCLK

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

(bit addressable)

0xC8

Figure 15.13. TMR2CN: Timer 2 Control Register

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Bits 7-0:

TMR2RLL: Timer 2 Reload Register Low Byte.
TMR2RLL holds the low byte of the reload value for Timer 2.

R/W

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xCA

Figure 15.14. TMR2RLL: Timer 2 Reload Register Low Byte

Figure 15.15. TMR2RLH: Timer 2 Reload Register High Byte

Bits 7-0:

TMR2RLH: Timer 2 Reload Register High Byte.
The TMR2RLH holds the high byte of the reload value for Timer 2.

R/W

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xCB

Figure 15.16. TMR2L: Timer 2 Low Byte

Bits 7-0:

TMR2L: Timer 2 Low Byte.
In 16-bit mode, the TMR2L register contains the low byte of the 16-bit Timer 2. In 8-bit mode,
TMR2L contains the 8-bit low byte timer value.

R/W

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xCC

Figure 15.17. TMR2H Timer 2 High Byte

Bits 7-0:

TMR2H: Timer 2 High Byte.
In 16-bit mode, the TMR2H register contains the high byte of the 16-bit Timer 2. In 8-bit mode,
TMR2H contains the 8-bit high byte timer value.

R/W

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xCD

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16.

PROGRAMMABLE COUNTER ARRAY

The Programmable Counter Array (PCA0) provides enhanced timer functionality while requiring less CPU interven-
tion than the standard 8051 counter/timers. The PCA consists of a dedicated 16-bit counter/timer and three 16-bit
capture/compare modules. Each capture/compare module has its own associated I/O line (CEXn) which is routed
through the Crossbar to Port I/O when enabled (See

Section "12.1. Priority Crossbar Decoder" on page 96

for

details on configuring the Crossbar). The counter/timer is driven by a programmable timebase that can select between
six sources: system clock, system clock divided by four, system clock divided by twelve, the external oscillator clock
source divided by 8, Timer 0 overflow, or an external clock signal on the ECI input pin. Each capture/compare mod-
ule may be configured to operate independently in one of six modes: Edge-Triggered Capture, Software Timer, High-
Speed Output, Frequency Output, 8-Bit PWM, or 16-Bit PWM (each mode is described in

Section "16.2. Capture/

Compare Modules" on page 147

). The external oscillator clock option is ideal for real-time clock (RTC) functional-

ity, allowing the PCA to be clocked by a precision external oscillator while the internal oscillator drives the system
clock. The PCA is configured and controlled through the system controller's Special Function Registers. The basic
PCA block diagram is shown in Figure 16.1.

Important Note: The PCA Module 2 may be used as a watchdog timer (WDT), and is enabled in this mode follow-
ing a system reset. Access to certain PCA registers is restricted while WDT mode is enabled. See

Section 16.3

for

details.

16-Bit Counter/Timer

EX1

Digital Crossbar

CE
X

Port I/O

Capture/Compare

Module 1

Capture/Compare

Module 0

Capture/Compare

Module 2 / WDT

PCA

CLOCK

MUX

SYSCLK/12

SYSCLK/4

Timer 0 Overflow

ECI

SYSCLK

External Clock/8

Figure 16.1. PCA Block Diagram

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16.1.

PCA Counter/Timer

The 16-bit PCA counter/timer consists of two 8-bit SFRs: PCA0L and PCA0H. PCA0H is the high byte (MSB) of the
16-bit counter/timer and PCA0L is the low byte (LSB). Reading PCA0L automatically latches the value of PCA0H
into a "snapshot" register; the following PCA0H read accesses this "snapshot" register. Reading the PCA0L Regis-
ter first guarantees an accurate reading of the entire 16-bit PCA0 counter. Reading PCA0H or PCA0L does not
disturb the counter operation. The CPS2-CPS0 bits in the PCA0MD register select the timebase for the counter/timer
as shown in Table 16.1. Note that in `External oscillator source divided by 8' mode, the external oscillator
source is synchronized with the system clock, and must have a frequency less than or equal to the system clock.

When the counter/timer overflows from 0xFFFF to 0x0000, the Counter Overflow Flag (CF) in PCA0MD is set to
logic 1 and an interrupt request is generated if CF interrupts are enabled. Setting the ECF bit in PCA0MD to logic 1
enables the CF flag to generate an interrupt request. The CF bit is not automatically cleared by hardware when the
CPU vectors to the interrupt service routine, and must be cleared by software (Note: PCA0 interrupts must be glo-
bally enabled before CF interrupts are recognized. PCA0 interrupts are globally enabled by setting the EA bit and the
EPCA0 bit to logic 1). Clearing the CIDL bit in the PCA0MD register allows the PCA to continue normal operation
while the CPU is in Idle mode.

Table 16.1. PCA Timebase Input Options

CPS2

CPS1

CPS0

Timebase

System clock divided by 12

System clock divided by 4

Timer 0 overflow

High-to-low transitions on ECI (max rate = system clock divided by 4)

System clock

External oscillator source divided by 8

External oscillator source divided by 8 is synchronized with the system clock.

Figure 16.2. PCA Counter/Timer Block Diagram

PCA0CN

C
R

C
C

F
0

C
C

F
2

C
C

F
1

SYSCLK/12

SYSCLK/4

Timer 0 Overflow

ECI

000

001

010

011

PCA0MD

D
T
E

E
C
F

C
P
S

C
K

C
P
S

IDLE

100

101

SYSCLK

External Clock/8

PCA0H

PCA0L

Snapshot

To SFR Bus

Overflow

To PCA Interrupt System

PCA0L

read

To PCA Modules

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16.2.

Capture/Compare Modules

Each module can be configured to operate independently in one of six operation modes: Edge-triggered Capture,
Software Timer, High Speed Output, Frequency Output, 8-Bit Pulse Width Modulator, or 16-Bit Pulse Width Modu-
lator. Each module has Special Function Registers (SFRs) associated with it in the CIP-51 system controller. These
registers are used to exchange data with a module and configure the module's mode of operation.

Table 16.2 summarizes the bit settings in the PCA0CPMn registers used to select the PCA capture/compare module's
operating modes. Setting the ECCFn bit in a PCA0CPMn register enables the module's CCFn interrupt. Note: PCA0
interrupts must be globally enabled before individual CCFn interrupts are recognized. PCA0 interrupts are globally
enabled by setting the EA bit and the EPCA0 bit to logic 1. See Figure 16.3 for details on the PCA interrupt configu-
ration.

Table 16.2. PCA0CPM Register Settings for PCA Capture/Compare Modules

PWM16

ECOM

CAPP CAPN

MAT

TOG

PWM

ECCF

Operation Mode

Capture triggered by positive edge on

CEXn

Capture triggered by negative edge on

CEXn

Capture triggered by transition on

CEXn

Software Timer

High Speed Output

Frequency Output

8-Bit Pulse Width Modulator

16-Bit Pulse Width Modulator

X = Don't Care

Figure 16.3. PCA Interrupt Block Diagram

PCA0CN

C
R

C
C

F
0

C
C

F
2

C
C
F

PCA0MD

W
D

T
E

E
C
F

C
P
S

W
D

C
K

C
P
S

PCA Module 0

(CCF0)

PCA Module 1

(CCF1)

ECCF1

ECCF0

PCA Module 2

(CCF2)

ECCF2

PCA Counter/

Timer Overflow

PCA0CPMn

(for n = 0 to 2)

1
6
n

E
C

O
M

E
C
C
F

O
G

C
A
P
P

C
A
P
N

A
T

Interrupt
Priority
Decoder

EPCA0

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16.2.1. Edge-triggered Capture Mode

In this mode, a valid transition on the CEXn pin causes the PCA to capture the value of the PCA counter/timer and
copy it into the corresponding module's 16-bit capture/compare register (PCA0CPLn and PCA0CPHn). The CAPPn
and CAPNn bits in the PCA0CPMn register are used to select the type of transition that triggers the capture: low-to-
high transition (positive edge), high-to-low transition (negative edge), or either transition (positive or negative edge).
When a capture occurs, the Capture/Compare Flag (CCFn) in PCA0CN is set to logic 1 and an interrupt request is
generated if CCF interrupts are enabled. The CCFn bit is not automatically cleared by hardware when the CPU vec-
tors to the interrupt service routine, and must be cleared by software. If both CAPPn and CAPNn bits are set to
logic 1, then the state of the Port pin associated with CEXn can be read directly to determine whether a rising-edge or
falling-edge caused the capture.

Note: The CEXn input signal must remain high or low for at least 2 system clock cycles to be recognized by the hard-
ware.

Figure 16.4. PCA Capture Mode Diagram

PCA0L

PCA0CPLn

PCA
Timebase

CEXn

Crossbar

Port I/O

PCA0H

Capture

PCA0CPHn

)

PCA0CPMn

W
M

1
6
n

E
C

O
M

E
C
C
F

O
G

W
M

C
A
P
P

C
A
P
N

A
T

PCA0CN

C
R

C
C

F
0

C
C

F
2

C
C

F
1

PCA Interrupt

0 0 0 x

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16.2.2. Software Timer (Compare) Mode

In Software Timer mode, the PCA counter/timer value is compared to the module's 16-bit capture/compare register
(PCA0CPHn and PCA0CPLn). When a match occurs, the Capture/Compare Flag (CCFn) in PCA0CN is set to
logic 1 and an interrupt request is generated if CCF interrupts are enabled. The CCFn bit is not automatically cleared
by hardware when the CPU vectors to the interrupt service routine, and must be cleared by software. Setting the
ECOMn and MATn bits in the PCA0CPMn register enables Software Timer mode.

Important Note About Capture/Compare Registers: When writing a 16-bit value to the PCA0 Capture/Compare
registers, the low byte should always be written first. Writing to PCA0CPLn clears the ECOMn bit to `0'; writing to
PCA0CPHn sets ECOMn to `1'.

Figure 16.5. PCA Software Timer Mode Diagram

Match

16-bit Comparator

PCA0H

PCA0CPHn

Enable

PCA0L

PCA
Timebase

PCA0CPLn

0 0

ENB

Write to

PCA0CPLn

Write to

PCA0CPHn

Reset

PCA0CPMn

W
M

1
6
n

E
C

O
M

E
C
C
F

O
G

C
A
P
P

C
A
P
N

A
T

PCA0CN

C
R

C
C

F
0

C
C

F
2

C
C

F
1

PCA Interrupt

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16.2.4. Frequency Output Mode

Frequency Output Mode produces a programmable-frequency square wave on the module's associated CEXn pin.
The capture/compare module high byte holds the number of PCA clocks to count before the output is toggled. The
frequency of the square wave is then defined by Equation 16.1.

Where F

PCA

is the frequency of the clock selected by the CPS2-0 bits in the PCA mode register, PCA0MD. The

lower byte of the capture/compare module is compared to the PCA counter low byte; on a match, CEXn is toggled
and the offset held in the high byte is added to the matched value in PCA0CPLn. Frequency Output Mode is enabled
by setting the ECOMn, TOGn, and PWMn bits in the PCA0CPMn register.

Equation 16.1. Square Wave Frequency Output

CEXn

PCA

PCA0CPHn

-----------------------------------------

8-bit

Comparator

PCA0L

Enable

PCA Timebase

match

PCA0CPHn

8-bit Adder

PCA0CPLn

Adder

Enable

CEXn

Crossbar

Port I/O

Toggle

TOGn

0 0 0

PCA0CPMn

W
M

1
6
n

E
C

O
M

E
C
C
F

O
G

C
A
P
P

C
A
P
N

A
T
n

ENB

Write to

PCA0CPLn

Write to

PCA0CPHn

Reset

Figure 16.7. PCA Frequency Output Mode

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16.2.5. 8-Bit Pulse Width Modulator Mode

Each module can be used independently to generate a pulse width modulated (PWM) output on its associated CEXn
pin. The frequency of the output is dependent on the timebase for the PCA counter/timer. The duty cycle of the PWM
output signal is varied using the module's PCA0CPLn capture/compare register. When the value in the low byte of the
PCA counter/timer (PCA0L) is equal to the value in PCA0CPLn, the output on the CEXn pin will be set to `1'. When
the count value in PCA0L overflows, the CEXn output will be set to `0' (see Figure 16.8). Also, when the counter/
timer low byte (PCA0L) overflows from 0xFF to 0x00, PCA0CPLn is reloaded automatically with the value stored in
the module's capture/compare high byte (PCA0CPHn) without software intervention. Setting the ECOMn and
PWMn bits in the PCA0CPMn register enables 8-Bit Pulse Width Modulator mode. The duty cycle for 8-Bit PWM
Mode is given by Equation 16.2.

Using Equation 16.2, the largest duty cycle is 100% (PCA0CPHn = 0), and the smallest duty cycle is 0.39%
(PCA0CPHn = 0xFF). A 0% duty cycle may be generated by clearing the ECOMn bit to `0'.

DutyCycle

256

PCA0CPHn

(

)

256

---------------------------------------------------

Equation 16.2. 8-Bit PWM Duty Cycle

8-bit

Comparator

PCA0L

PCA0CPLn

PCA0CPHn

CEXn

Crossbar

Port I/O

Enable

Overflow

PCA Timebase

0 0 x 0

SET

CLR

match

PCA0CPMn

1
6
n

E
C
O
M

E
C
C
F

O
G

C
A
P
P

C
A
P
N

A
T

ENB

Write to

PCA0CPLn

Write to

PCA0CPHn

Reset

Figure 16.8. PCA 8-Bit PWM Mode Diagram

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16.2.6. 16-Bit Pulse Width Modulator Mode

A PCA module may also be operated in 16-Bit PWM mode. In this mode, the 16-bit capture/compare module defines
the number of PCA clocks for the low time of the PWM signal. When the PCA counter matches the module contents,
the output on CEXn is set to `1'; when the counter overflows, CEXn is set to `0'. To output a varying duty cycle, new
value writes should be synchronized with PCA CCFn match interrupts. 16-Bit PWM Mode is enabled by setting the
ECOMn, PWMn, and PWM16n bits in the PCA0CPMn register. For a varying duty cycle, match interrupts should be
enabled (ECCFn = 1 AND MATn = 1) to help synchronize the capture/compare register writes. The duty cycle for 16-
Bit PWM Mode is given by Equation 16.3.

Using Equation 16.3, the largest duty cycle is 100% (PCA0CPn = 0), and the smallest duty cycle is 0.0015%
(PCA0CPn = 0xFFFF). A 0% duty cycle may be generated by clearing the ECOMn bit to `0'.

Equation 16.3. 16-Bit PWM Duty Cycle

DutyCycle

65536

PCA0CPn

(

)

65536

-----------------------------------------------------

Figure 16.9. PCA 16-Bit PWM Mode

PCA0CPLn

PCA0CPHn

Enable

PCA Timebase

0 0 x 0

PCA0CPMn

W
M

1
6
n

E
C

O
M

E
C
C
F

O
G

C
A
P
P

C
A
P
N

M
A

T
n

16-bit Comparator

CEXn

Crossbar

Port I/O

Overflow

SET

CLR

match

PCA0H

PCA0L

ENB

Write to

PCA0CPLn

Write to

PCA0CPHn

Reset

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16.3.

Watchdog Timer Mode

A programmable watchdog timer (WDT) function is available through the PCA Module 2. The WDT is used to gen-
erate a reset if the time between writes to the WDT update register (PCA0CPH2) exceed a specified limit. The WDT
can be configured and enabled/disabled as needed by software.

With the WDTE bit set in the PCA0MD register, Module 2 operates as a watchdog timer (WDT). The Module 2 high
byte is compared to the PCA counter high byte; the Module 2 low byte holds the offset to be used when WDT updates
are performed. The Watchdog Timer is enabled on reset. Writes to some PCA registers are restricted while the
Watchdog Timer is enabled.

16.3.1. Watchdog Timer Operation

While the WDT is enabled:

PCA counter is forced on.

Writes to PCA0L and PCA0H are not allowed.

PCA clock source bits (CPS2-CPS0) are frozen.

PCA Idle control bit (CIDL) is frozen.

Module 2 is forced into software timer mode.

Writes to the module 2 mode register (PCA0CPM2) are disabled.

While the WDT is enabled, writes to the CR bit will not change the PCA counter state; the counter will run until the
WDT is disabled. The PCA counter run control (CR) will read zero if the WDT is enabled but user software has not
enabled the PCA counter. If a match occurs between PCA0CPH2 and PCA0H while the WDT is enabled, a reset will
be generated. To prevent a WDT reset, the WDT may be updated with a write of any value to PCA0CPH2. Upon a
PCA0CPH2 write, PCA0H plus the offset held in PCA0CPL2 is loaded into PCA0CPH2 (See Figure 16.10).

Figure 16.10. PCA Module 2 with Watchdog Timer Enabled

PCA0H

Enable

PCA0L Overflow

Reset

PCA0CPL2

8-bit Adder

PCA0CPH2

Adder

Enable

PCA0MD

D
T
E

E
C
F

C
P
S

C
K

C
P
S

Match

Write to

PCA0CPH2

8-bit

Comparator

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Note that the 8-bit offset held in PCA0CPH2 is compared to the upper byte of the 16-bit PCA counter. This offset
value is the number of PCA0L overflows before a reset. Up to 256 PCA clocks may pass before the first PCA0L
overflow occurs, depending on the value of the PCA0L when the update is performed. The total offset is then given
(in PCA clocks) by Equation 16.4, where PCA0L is the value of the PCA0L register at the time of the update.

The WDT reset is generated when PCA0L overflows while there is a match between PCA0CPH2 and PCA0H. Soft-
ware may force a WDT reset by writing a `1' to the CCF2 flag (PCA0CN.2) while the WDT is enabled.

16.3.2. Watchdog Timer Usage

To configure the WDT, perform the following tasks:

Disable the WDT by writing a `0' to the WDTE bit.

Select the desired PCA clock source (with the CPS2-CPS0 bits).

Load PCA0CPL2 with the desired WDT update offset value.

Configure the PCA Idle mode (set CIDL if the WDT should be suspended while the CPU is in Idle mode).

Enable the WDT by setting the WDTE bit to `1'.

The PCA clock source and Idle mode select cannot be changed while the WDT is enabled. The Watchdog Timer is
enabled by setting the WDTE or WDLCK bits in the PCA0MD register. When WDLCK is set, the WDT cannot be
disabled until the next system reset. If WDLCK is not set, the WDT is disabled by clearing the WDTE bit.

The WDT is enabled following any reset. The PCA0 counter clock defaults to the system clock divided by 12,
PCA0L defaults to 0x00, and PCA0CPL2 defaults to 0x00. Using Equation 16.4, this results in a WDT timeout inter-
val of 3072 system clock cycles. Table 16.3 lists some example timeout intervals for typical system clocks, assuming
SYSCLK / 12 as the PCA clock source.

Table 16.3. Watchdog Timer Timeout Intervals

System Clock (Hz)

PCA0CPL2

Timeout Interval (ms)

24,500,000

255

32.1

24,500,000

128

16.2

24,500,000

4.1

18,432,000

255

42.7

18,432,000

128

21.5

18,432,000

5.5

11,059,200

255

71.1

11,059,200

128

35.8

11,059,200

9.2

3,060,000

255

257

3,060,000

128

129.5

3,060,000

33.1

32,000

255

24576

32,000

128

12384

32,000

3168

Assumes SYSCLK / 12 as the PCA clock source, and a PCA0L value of 0x00 at the update

time.

Internal oscillator reset frequency.

Equation 16.4. Watchdog Timer Offset in PCA Clocks

Offset

256

PCA0CPL2

(

)

256

PCA0L

(

)

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16.4.

Register Descriptions for PCA

Following are detailed descriptions of the special function registers related to the operation of the PCA.

Bit7:

CF: PCA Counter/Timer Overflow Flag.
Set by hardware when the PCA Counter/Timer overflows from 0xFFFF to 0x0000. When the
Counter/Timer Overflow (CF) interrupt is enabled, setting this bit causes the CPU to vector to the
PCA interrupt service routine. This bit is not automatically cleared by hardware and must be cleared
by software.

Bit6:

CR: PCA Counter/Timer Run Control.
This bit enables/disables the PCA Counter/Timer.
0: PCA Counter/Timer disabled.
1: PCA Counter/Timer enabled.

Bits5-3:

UNUSED. Read = 000b, Write = don't care.

Bit2:

CCF2: PCA Module 2 Capture/Compare Flag.
This bit is set by hardware when a match or capture occurs. When the CCF2 interrupt is enabled, set-
ting this bit causes the CPU to vector to the PCA interrupt service routine. This bit is not automati-
cally cleared by hardware and must be cleared by software.

Bit1:

CCF1: PCA Module 1 Capture/Compare Flag.
This bit is set by hardware when a match or capture occurs. When the CCF1 interrupt is enabled, set-
ting this bit causes the CPU to vector to the PCA interrupt service routine. This bit is not automati-
cally cleared by hardware and must be cleared by software.

Bit0:

CCF0: PCA Module 0 Capture/Compare Flag.
This bit is set by hardware when a match or capture occurs. When the CCF0 interrupt is enabled, set-
ting this bit causes the CPU to vector to the PCA interrupt service routine. This bit is not automati-
cally cleared by hardware and must be cleared by software.

R/W

Reset Value

CCF2

CCF1

CCF0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

(bit addressable)

0xD8

Figure 16.11. PCA0CN: PCA Control Register

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Figure 16.12. PCA0MD: PCA Mode Register

Bit7:

CIDL: PCA Counter/Timer Idle Control.
Specifies PCA behavior when CPU is in Idle Mode.
0: PCA continues to function normally while the system controller is in Idle Mode.
1: PCA operation is suspended while the system controller is in Idle Mode.

Bit6:

WDTE: Watchdog Timer Enable
If this bit is set, PCA Module 2 is used as the Watchdog Timer.
0: Watchdog Timer disabled.
1: PCA Module 2 enabled as Watchdog Timer.

Bit5:

WDLCK: Watchdog Timer Lock
This bit locks/unlocks the Watchdog Timer Enable. When WDLCK is set, the Watchdog Timer may
not be disabled until the next system reset.
0: Watchdog Timer Enable unlocked.
1: Watchdog Timer Enable locked.

Bit4:

UNUSED. Read = 0b, Write = don't care.

Bits3-1:

CPS2-CPS0: PCA Counter/Timer Pulse Select.
These bits select the clock source for the PCA counter

Bit0:

ECF: PCA Counter/Timer Overflow Interrupt Enable.
This bit sets the masking of the PCA Counter/Timer Overflow (CF) interrupt.
0: Disable the CF interrupt.
1: Enable a PCA Counter/Timer Overflow interrupt when CF (PCA0CN.7) is set.

Note: When the WDTE bit is set to `1', the PCA0MD register cannot be modified. To change the contents

of the PCA0MD register, the Watchdog Timer must first be disabled.

R/W

Reset Value

CIDL

WDTE

WDLCK

CPS2

CPS1

CPS0

ECF

01000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xD9

CPS2

CPS1

CPS0

Timebase

System clock divided by 12

System clock divided by 4

Timer 0 overflow

High-to-low transitions on ECI (max rate = system clock divided
by 4)

System clock

External clock divided by 8

Reserved

External oscillator source divided by 8 is synchronized with the system clock.

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PCA0CPMn Address:

PCA0CPM0 = 0xDA (n = 0)
PCA0CPM1 = 0xDB (n = 1)
PCA0CPM2 = 0xDC (n = 2)

Bit7:

PWM16n: 16-bit Pulse Width Modulation Enable.
This bit selects 16-bit mode when Pulse Width Modulation mode is enabled (PWMn = 1).
0: 8-bit PWM selected.
1: 16-bit PWM selected.

Bit6:

ECOMn: Comparator Function Enable.
This bit enables/disables the comparator function for PCA Module n.
0: Disabled.
1: Enabled.

Bit5:

CAPPn: Capture Positive Function Enable.
This bit enables/disables the positive edge capture for PCA Module n.
0: Disabled.
1: Enabled.

Bit4:

CAPNn: Capture Negative Function Enable.
This bit enables/disables the negative edge capture for PCA Module n.
0: Disabled.
1: Enabled.

Bit3:

MATn: Match Function Enable.
This bit enables/disables the match function for PCA Module n. When enabled, matches of the PCA
counter with a module's capture/compare register cause the CCFn bit in PCA0MD register to be set to
logic 1.
0: Disabled.
1: Enabled.

Bit2:

TOGn: Toggle Function Enable.
This bit enables/disables the toggle function for PCA Module n. When enabled, matches of the PCA
counter with a module's capture/compare register cause the logic level on the CEXn pin to toggle. If
the PWMn bit is also set to logic 1, the module operates in Frequency Output Mode.
0: Disabled.
1: Enabled.

Bit1:

PWMn: Pulse Width Modulation Mode Enable.
This bit enables/disables the PWM function for PCA Module n. When enabled, a pulse width modu-
lated signal is output on the CEXn pin. 8-bit PWM is used if PWM16n is cleared; 16-bit mode is used
if PWM16n is set to logic 1. If the TOGn bit is also set, the module operates in Frequency Output
Mode.
0: Disabled.
1: Enabled.

Bit0:

ECCFn: Capture/Compare Flag Interrupt Enable.
This bit sets the masking of the Capture/Compare Flag (CCFn) interrupt.
0: Disable CCFn interrupts.
1: Enable a Capture/Compare Flag interrupt request when CCFn is set.

R/W

Reset Value

PWM16n

ECOMn

CAPPn

CAPNn

MATn

TOGn

PWMn

ECCFn

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xDA, 0xDB,

0xDC

Figure 16.13. PCA0CPMn: PCA Capture/Compare Mode Registers

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17.

C2 INTERFACE

C8051F300/1/2/3/4/5 devices include an on-chip Cygnal 2-Wire (C2) debug interface to allow FLASH programming,
boundary scan functions, and in-system debugging with the production part installed in the end application. The C2
interface operates similar to JTAG, where the three JTAG data signals (TDI, TDO, TMS) are mapped into one bi-
directional C2 data signal (C2D). See the C2 Interface Specification for details on the C2 protocol.

17.1.

C2 Interface Registers

The following describes the C2 registers necessary to perform FLASH programming and boundary scan functions
through the C2 interface. All C2 registers are accessed through the C2 interface as described in the C2 Interface Spec-
ification.

Figure 17.1. C2ADD: C2 Address Register

Bits7-0:

The C2ADD register is accessed via the C2 interface to select the target Data register for C2 Data
Read and Data Write commands.

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

Address

Description

0x00

Selects the Device ID register for Data Read instructions

0x01

Selects the Revision ID register for Data Read instructions

0x02

Selects the C2 FLASH Programming Control register for Data
Read/Write instructions

0xB4

Selects the C2 FLASH Programming Data register for Data Read/Write
instructions

0x80

Selects the Port0 register for Data Read/Write instructions

0xF1

Selects the Port0 Input Mode register for Data Read/Write instructions

0xA4

Selects the Port0 Output Mode register for Data Read/Write instructions

Figure 17.2. DEVICEID: C2 Device ID Register

This read-only register returns the 8-bit device ID: 0x04 (C8051F300/1/2/3).

Reset Value

00000100

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

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Figure 17.3. REVID: C2 Revision ID Register

This read-only register returns the 8-bit revision ID: 0x00 (Revision A)

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

Figure 17.4. FPCTL: C2 FLASH Programming Control Register

Bits7-0

FPCTL: FLASH Programming Control Register
This register is used to enable FLASH programming via the C2 interface. To enable C2 FLASH
programming, the following codes must be written in order: 0x02, 0x01. Note that once C2 FLASH
programming is enabled, a system reset must be issued to resume normal operation.

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

Figure 17.5. FPDAT: C2 FLASH Programming Data Register

Bits7-0:

FPDAT: C2 FLASH Programming Data Register
This register is used to pass FLASH commands, addresses, and data during C2 FLASH accesses.
Valid commands are listed below.

Reset Value

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

Code

Command

0x06

FLASH Block Read

0x07

FLASH Block Write

0x08

FLASH Page Erase

0x03

Device Erase

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Disclaimers

Life support: These products are not designed for use in life support appliances or systems where malfunction of
these products can reasonably be expected to result in personal injury. Cygnal Integrated Products customers using or
selling these products for use in such applications do so at their own risk and agree to fully indemnify Cygnal Inte-
grated Products for any damages resulting from such applications.

Right to make changes: Cygnal Integrated Products reserves the right to make changes, without notice, in the prod-
ucts, including circuits and/or software, described or contained herein in order to improve design and/or performance.
Cygnal Integrated Products assumes no responsibility or liability for the use of any of these products, conveys no
license or title under any patent, copyright, or mask work right to these products, and makes no representations or
warranties that these products are free from patent, copyright, or mask work infringement, unless otherwise specified.

CIP-51 is a trademark of Cygnal Integrated Products, Inc.
MCS-51 and SMBus are trademarks of Intel Corporation.

C is a trademark of Philips Semiconductor.

CYGNAL INTEGRATED PRODUCTS

4301 Westbank Drive

Suite B-100

Austin, TX 78746

www.cygnal.com

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