FDC37C665GT
FDC37C666GT

High-Performance Multi-Mode

Parallel Port Super I/O Floppy Disk Controllers

FEATURES

5 Volt Operation

Floppy Disk Available on Parallel Port Pins

2.88MB Super I/O Floppy Disk Controller

- Licensed CMOS 765B Floppy Disk

Controller

- Software and Register Compatible to the

82077AA Using SMSC's Proprietary
Floppy Disk Controller Core

- Supports Vertical Recording Format
- 100% IBM® Compatibility
- Detects All Overrun and Underrun

Conditions

- 48 mA Drivers and Schmitt Trigger

Inputs

- DMA Enable Logic
- Data Rate and Drive Control Registers
- Swap Drives A and B
- Non-Burst Mode DMA Option
- FDC Primary/Secondary Address

Selection

- 16 Byte Data FIFO
- Low Power CMOS 0.8

Design

Enhanced Digital Data Separator

- Low Cost Implementation - 24 MHz

Crystal

- No Filter Components Required
- Ease of Test and Use, Lower System

Cost, and Reduced Board Area

- 1 Mb/s, 500 Kb/s, 300 Kb/s, 250 Kb/s

Data Rates

- Supports Floppy Disk and Tape Drives
- Programmable Precompensation Modes

Multi-Mode Parallel Port with ChiProtect

Circuitry
- Standard Mode

- IBM PC/XT®, PC/AT®, and PS/2

Compatible Bidirectional Parallel
Port

- Enhanced Mode

- Enhanced Parallel Port (EPP)

Compatible - EPP 1.7 and EPP 1.9
(IEEE 1284 Compliant)

- High Speed Mode

- Microsoft and Hewlett Packard

Extended Capabilities Port (ECP) IEEE
1284 Compliant

- Incorporates ChiProtect Circuitry for

Protection Against Damage Due to
Printer Power-On

- Provides Backdrive Current Protection
- 24 mA Output Drivers
- Two Parallel Port Interrupt Pins

Serial Ports

- Two High Speed NS16C550 Compatible

UARTs with Send/Receive 16 Byte
FIFOs

- MIDI Compatible
- Programmable Baud Rate Generator
- Modem Control Circuitry

ISA Host Interface

IDE Interface

- On-Chip Decode and Select Logic

Compatible with IBM PC/XT and PC/AT
Embedded Hard Disk Drives

- IDE Primary/Secondary Address

Selection

Supports Four Floppy Drives Directly

(Standard and Enhanced Modes)

General Purpose 11 Bit Address Decoder

Game Port Select Logic (FDC37C666GT

Only)

100 Pin QFP Package

TABLE OF CONTENTS

FEATURES ...................................................................................................................................... 1

GENERAL DESCRIPTION................................................................................................................ 3

PIN CONFIGURATION...................................................................................................................... 4

DESCRIPTION OF PIN FUNCTIONS ................................................................................................ 5

FUNCTIONAL DESCRIPTION ........................................................................................................ 22

SUPER I/O REGISTERS ...........................................................................................................22

HOST PROCESSOR INTERFACE............................................................................................ 22

FLOPPY DISK CONTROLLER.................................................................................................. 23

FLOPPY DISK CONTROLLER INTERNAL REGISTERS ............................................................23

COMMAND SET/DESCRIPTIONS .................................................................................................. 46

INSTRUCTION SET ........................................................................................................................ 50

PARALLEL PORT FLOPPY DISK CONTROLLER.............................................................................76

SERIAL PORT (UART) .................................................................................................................... 78

PARALLEL PORT........................................................................................................................... 92

IBM XT/AT COMPATIBLE, BI-DIRECTIONAL AND EPP MODES...............................................94

EXTENDED CAPABILITIES PARALLEL PORT ........................................................................100

INTEGRATED DRIVE ELECTRONICS INTERFACE ..................................................................... 113

CONFIGURATION......................................................................................................................... 117

OPERATIONAL DESCRIPTION..................................................................................................... 131

MAXIMUM GUARANTEED RATINGS ..................................................................................... 131

DC ELECTRICAL CHARACTERISTICS ................................................................................. 131

TIMING DIAGRAMS ...................................................................................................................... 134

ECP PARALLEL PORT TIMING...............................................................................................147

GENERAL DESCRIPTION

The SMSC FDC37C665GT and FDC37C666GT
Advanced High Performance Multi-Mode
Parallel Port Super I/O Floppy Disk Controller
ICs utilize SMSC's proven SuperCell technology
for increased product reliability and functionality.
The FDC37C665GT is optimized for
motherboard applications while the
FDC37C666GT is oriented towards controller
card applications. Both devices support 1 Mb/s
data rates for vertical recording operation. The
FDC37C665GT is hardware compatible with the
FDC37C651 and FDC37C661 in the Standard
and Enhanced Parallel Port Modes.

The FDC37C665GT and FDC37C666GT
incorporate SMSC's true CMOS 765B floppy
disk controller, advanced digital data separator,
16 byte data FIFO, two 16C550 compatible
UARTs, one Multi-Mode parallel port which
includes ChiProtect circuitry plus EPP and ECP
support, IDE interface, on-chip 24 mA AT bus
drivers, game port chip select (FDC37C666GT
only), general purpose address decoder and
four floppy direct drive support. The true CMOS
765B core provides 100% compatibility with IBM
PC/XT and PC/AT architectures in addition to
providing data overflow and underflow
protection. The SMSC advanced digital data
separator incorporates SMSC's patented data
separator technology, allowing for ease of
testing and use. Both on-chip UARTs are
compatible with the NS16C550. The parallel
port, the IDE interface and the

game port select logic are compatible with IBM
PC/XT and PC/AT architectures, as well as EPP
and ECP. The FDC37C665GT and
FDC37C666GT incorporate sophisticated power
control circuitry (PCC). The PCC supports
multiple low power down modes.

The FDC37C665GT Floppy Disk Controller
incorporates Software Configurable Logic (SCL)
for ease of use. Use of the SCL feature allows
programmable system configuration of key
functions such as the FDC, parallel port, and
UARTs. The parallel port ChiProtect prevents
damage caused by the printer being powered
when the FDC37C665GT or FDC37C666GT is
not powered. The parallel port backdrive current
protection prevents the FDC37C665GT or
FDC37C666GT from sinking current when the
device is powered off and the printer is left
powered on.

The FDC37C665GT and FDC37C666GT do not
require any external filter components and are,
therefore, easy to use and offer lower system
cost and reduced board area. The
FDC37C665GT and FDC37C666GT are
software and register compatible to the
82077AA using SMSC's proprietary floppy disk
controller core.

IBM, PC/XT and PC/AT are registered trademarks and PS/2 is
a trademark of International Business Machines Corporation.
SMSC is a registered trademark and ChiProtect, SuperCell,
and Multi-Mode are trademarks of Standard Microsystems
Corporation

PIN CONFIGURATION

50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31

81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99

100

D2
D1
D0
VSS
AEN
nIOW
nIOR
A9
A8
A7
FINTR
PINTR
IRQ4
IRQ3
nDACK
TC
A6
A5
A4
A3

nRTS1
nCTS1
nDTR1

nRI1

nDCD1

nRI2

nDCD2

RXD2

TXD2

nDSR2
nRTS2
nCTS2
nDTR2

DRV2/ADRx/PINTR2

VSS

nMTR2/PDACK

nDS3/A10

nDS2/nDS3/PDIR

nMTR3/PDRQ

IOCHRDY

I
N

I
T

FDC37C665GT

I
O

I
D

/
C

/
M

I
A

I
D

/
M

I
A

I
D

I
N

I
R

80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 51

50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31

81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99

100

D2
D1
D0
VSS
AEN
nIOW
nIOR
A9
A8
A7
FINTR
PINTR
PSPIRQ
SSPIRQ
nDACK
TC
A6
A5
A4
A3

nRTS1
nCTS1
nDTR1

nRI1

nDCD1

nRI2

nDCD2

RXD2

TXD2

nDSR2
nRTS2
nCTS2
nDTR2

DRV2/ADRx/PINTR2

VSS

nMTR2/PDACK

nDS3/A10

nDS2/nDS3/PDIR

nMTR3/PDRQ

IOCHRDY

/
P

I
N

I
T

FDC37C666GT

I
O

/
F

/
I
D

I
D

/
C

/
M

I
A

I
D

/
M

I
A

I
D

I
N

I
R

80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 51

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

HOST PROCESSOR INTERFACE

48-51
53-56

Data Bus 0-7

D0-D7

I/O24

The data bus connection used by the host
microprocessor to transmit data to and from
the FDC37C665GT. These pins are in a
high-impedance state when not in the output
mode.

nI/O Read

nIOR

This active low signal is issued by the host
microprocessor to indicate a read operation.

nI/O Write

nIOW

This active low signal is issued by the host
microprocessor to indicate a write operation.

Address Enable

AEN

Active high Address Enable indicates DMA
operations on the host data bus. Used
internally to qualify appropriate address
decodes.

28-34
41-43

I/O Address

A0-A9

These host address bits determine the I/O
address to be accessed during nIOR and
nIOW cycles. These bits are latched
internally by the leading edge of nIOR and
nIOW.

FDC DMA
Request

FDRQ

O24

This active high output is the DMA request
for byte transfers of data to the host. This
signal is cleared on the last byte of the data
transfer by the nDACK signal going low (or
by nIOR going low if nDACK was already
low as in demand mode).

nDMA Acknowle-
dge

nDACK

An active low input acknowledging the
request for a DMA transfer of data. This
input enables the DMA read or write
internally.

Terminal Count

This signal indicates to the FDC37C665GT
that data transfer is complete. TC is only
accepted when nDACK or nPDACK is low.
In AT and PS/2 model 30 modes, TC is
active high and in PS/2 mode, TC is active
low.

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

Serial Port
Interrupt
Request

Primary Serial
Port Interrupt

IRQ4

PSPIRQ

O24

FDC37C665GT (Motherboard application):
IRQ4 is the interrupt from the Primary Serial
Port (PSP) or Secondary Serial Port (SSP)
when the PSP or SSP have their address
programmed as COM1 or COM3 (as
defined in the Configuration Registers). The
appropriate interrupt from the Serial Port is
enabled/disabled via the Interrupt Enable
Register (IER). The interrupt is reset
inactive after interrupt service. It is disabled
through IER or hardware reset.

FDC37C666GT (Adapter application):
PSPIRQ is a source of PSP interrupt.
Externally, it should be connected to either
IRQ3 or IRQ4 on PC/AT via jumpers.

Serial Port
Interrupt
Request

Secondary Serial
Port Interrupt

IRQ3

SSPIRQ

O24

FDC37C665GT (Motherboard application):
IRQ3 is the interrupt from the Primary Serial
Port (PSP) or secondary Serial Port (SSP)
when the PSP or SSP have their address
programmed as COM2 or COM4 (as
defined in the Configuration Registers). The
appropriate interrupt from the Serial Port is
enabled/disabled via the Interrupt Enable
Register (IER). The interrupt is reset
inactive after interrupt service. It is disabled
through IER or hardware reset.

FDC37C666GT (Adapter application):
SSPIRQ is a source of SSP interrupt.
Externally, it should be connected to either
IRQ3 or IRQ4 on PC/AT via jumpers.

Floppy
Controller
Interrupt
Request

FINTR

O24

This interrupt from the Floppy Disk
Controller is enabled/disabled via bit 3 of the
Digital Output Register (DOR).

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

Parallel Port
Interrupt
Request 1

PINTR1

O24

OD24

This interrupt from the Parallel Port is
enabled/disabled via bit 4 of the Parallel
Port Control Register. Refer to
configuration registers CR1 and CR3 for
more information.

If EPP or ECP Mode is enabled, this output
is pulsed low, then released to allow sharing
of interrupts.

Reset

RST

This active high signal resets the
FDC37C665GT and must be valid for 500
ns minimum. The effect on the internal
registers is described in the appropriate
section. The configuration registers are not
affected by this reset. In the
FDC37C666GT, the falling edge of reset
latches the jumper configuration. The
jumper select lines must be valid 50 ns prior
to this edge.

FLOPPY DISK INTERFACE

nRead Disk Data nRDATA

Raw serial bit stream from the disk drive,
low active. Each falling edge represents a
flux transition of the encoded data.

nWrite
Gate

nWGATE

OD48

This active low high current driver allows
current to flow through the write head. It
becomes active just prior to writing to the
diskette.

nWrite
Data

nWDATA

OD48

This active low high current driver provides
the encoded data to the disk drive. Each
falling edge causes a flux transition on the
media.

nHead
Select

nHDSEL

OD48

This high current output selects the floppy
disk side for reading or writing. A logic "1"
on this pin means side 0 will be accessed,
while a logic "0" means side 1 will be ac-
cessed.

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

nDirection
Control

nDIR

OD48

This high current low active output
determines the direction of the head
movement. A logic "1" on this pin means
outward motion, while a logic "0" means
inward motion.

nStep Pulse

nSTEP

OD48

This active low high current driver issues a
low pulse for each track-to-track movement
of the head.

nDisk Change

nDSKCHG

This input senses that the drive door is open
or that the diskette has possibly been
changed since the last drive selection. This
input is inverted and read via bit 7 of I/O
address 3F7H.

4,3

nDrive Select
O,1

nDS0,1

OD48

Active low open drain outputs select drives
0-1. Refer to Note 2.

nDrive Select 2

nDrive Select 3

PDIR

nDS2

nDS3

PDIR

OD48

Active low open drain output selects drives
2. Refer to Note 2.

In non-ECP mode: Active low open drain
output selects drive 3. Refer to Note 2.

This bit is used to indicate the direction of
the Parallel Port data bus. 0 = output/write
1 = input/read

nDrive Select 3

I/O Address 10

nDS3

A10

0D48

In non-ECP mode: Active low open drain
output selects drive 3. Refer to Note 2.

In ECP Mode, this pin is the A10 address
input.

2,5

nMotor On 0,1

nMTR0,1

OD48

These active low open drain outputs select
motor drives 0-1. Refer to Note 1.

nMotor On 2

nMTR2

nPDACK

OD48

Motor On 2: Refer to Note 1.

In ECP Mode, nMTR2 is the Parallel Port
DMA Acknowledge input. Active Low.

nMotor On 3

nMTR3

PDRQ

OD48

O24

Motor On 3: Refer to Note 1.

In ECP Mode, MTR3 is the Parallel Port
DMA Request output. Active High.

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

Density Select

DENSEL

OD48

Indicates whether a low (250/300 Kb/s) or
high (500 Kb/s) data rate has been selected.
This is determined by the IDENT bit in
Configuration Register 3.

nWrite
Protected

nWRTPRT

This active low Schmitt Trigger input senses
from the disk drive that a disk is write
protected. Any write command is ignored.

nTrack 00

nTR0

This active low Schmitt Trigger input senses
from the disk drive that the head is
positioned over the outermost track.

nIndex

nINDEX

This active low Schmitt Trigger input senses
from the disk drive that the head is
positioned over the beginning of a track, as
marked by an index hole.

19,18

Data Rate 0,
Data Rate 1

Media ID0,
Media ID1

DRATE0,
DRATE1

O24

These two outputs reflect bits 0 and 1
respectively of the Data Rate Register. At
power on, these two outputs are in a high
impedance state (refer to Table 50).

In Floppy Enhanced Mode 2 - These bits are
the Media ID 0,1 inputs. The value of these
bits can be read as bits 6 and 7 of the
Floppy Tape register.

SERIAL PORT INTERFACE

78,88

Receive Data

RXD1,
RXD2

Receiver serial data input.

Transmit Data

TXD1

PCF0

Transmitter serial data output from Primary
Serial Port.

FDC37C666GT (Adapter Mode): Parallel
Port Configuration Control 0. During reset
active this input is read and latched to
define the address of the Parallel Port.

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

nRequest to
Send

Parallel Port
Configuration
Control

nRTS1

PCF1

Active low Request to Send output for
Primary Serial Port. Handshake output
signal notifies modem that the UART is
ready to transmit data. This signal can be
programmed by writing to bit 1 of Modem
Control Register (MCR). The hardware
reset will reset the nRTS signal to inactive
mode (high). Forced inactive during loop
mode operation.

FDC37C666GT (Adapter Mode): Parallel
Port Configuration Control 1. During reset
active this input is read and latched to
define the address of the Parallel Port.

nRequest to
Send

Secondary Serial
Port
Configuration
Control

nRTS2

S2CF0

Active low Request to Send output for
Secondary Serial Port. Handshake output
signal notifies modem that the UART is
ready to transmit data. This signal can be
programmed by writing to bit 1 of Modem
Control Register (MCR). The hardware
reset will reset the nRTS signal to inactive
mode (high). Forced inactive during loop
mode operation.

FDC37C666GT (Adapter Mode): Secondary
Serial Port Configuration Control 0. During
Reset active this input is read and latched to
define the address of the Secondary Serial
Port.

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

nData Terminal
Ready

IDE
Configuration
Control

nDTR1

IDECF

Active low Data Terminal Ready output for
primary serial port. Handshake output
signal notifies modem that the UART is
ready to establish data communication link.
This signal can be programmed by writing
to bit 0 of Modem Control Register (MCR).
The hardware reset will reset the nDTR
signal to inactive mode (high). Forced
inactive during loop mode operation.

FDC37C666GT (Adapter Mode): IDE
Configuration Control. During reset active
this input is read and latched to
enable/disable the IDE.

nData Terminal
Ready

Secondary Serial
Port
Configuration
Control 1

nDTR2

S2CF1

Active low Data Terminal Ready output for
secondary serial port. Handshake output
signal notifies modem that the UART is
ready to establish data communication link.
This signal can be programmed by writing
to bit 0 of Modem Control Register (MCR),
The hardware reset will reset the nDTR
signal to inactive mode (high). Forced
inactive during loop mode operation.

FDC37C666GT (Adapter Mode): Secondary
Serial Port Configuration Control 1. During
reset active this input is read and latched to
define the address of the Secondary Serial
Port.

Transmit Data 2

TXD2

FDCCF

Transmitter Serial Data output from
Secondary Serial Port.

FDC37C666GT (Adapter Mode): Floppy
Disk Configuration. This input is read and
latched during Reset to enable/disable the
Floppy Disk Controller.

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

82,92

nClear to Send

nCTS1,
nCTS2

Active low Clear to Send inputs for primary
and secondary serial ports. Handshake
signal which notifies the UART that the
modem is ready to receive data. The CPU
can monitor the status of nCTS signal by
reading bit 4 of Modem Status Register
(MSR). A nCTS signal state change from
low to high after the last MSR read will set
MSR bit 0 to a 1. If bit 3 of Interrupt Enable
Register is set, the interrupt is generated
when nCTS changes state. The nCTS
signal has no effect on the transmitter.
Note: Bit 4 of MSR is the complement of
nCTS.

80,90

nData Set Ready nDSR1,

nDSR2

Active low Data Set Ready inputs for
primary and secondary serial ports.
Handshake signal which notifies the UART
that the modem is ready to establish the
communication link. The CPU can monitor
the status of nDSR signal by reading bit 5 of
Modem Status Register (MSR). A nDSR
signal state change from low to high after
the last MSR read will set MSR bit 1 to a 1.
If bit 3 of Interrupt Enable Register is set,
the interrupt is generated when nDSR
changes state. Note: Bit 5 of MSR is the
complement of nDSR.

85,87

nData Carrier
Detect

nDCD1,
nDCD2

Active low Data Carrier Detect inputs for
primary and secondary serial ports.
Handshake signal which notifies the UART
that carrier signal is detected by the
modem. The CPU can monitor the status of
nDCD signal by reading bit 7 of Modem
Status Register (MSR). A nDCD signal
state change from low to high after the last
MSR read will set MSR bit 3 to a 1. If bit 3
of Interrupt Enable Register is set, the
interrupt is generated when nDCD changes
state. Note: Bit 7 of MSR is the
complement of nDCD.

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

84,86

nRing Indicator

nRI1, nRI2

Active low Ring Indicator input for primary
and secondary serial ports. Handshake
signal which notifies the UART that the
telephone ring signal is detected by the
modem. The CPU can monitor the status of
nRI signal by reading bit 6 of Modem Status
Register (MSR). A nRI signal state change
from low to high after the last MSR read will
set MSR bit 2 to a 1. If bit 3 of Interrupt
Enable Register is set, the interrupt is
generated when nRI changes state. Note:
Bit 6 of MSR is the complement of nRI.

Drive 2

nADRx

Parallel Port
Interrupt
Request 2

DRV2

nADRx

PINTR2

ECPEN

O24

In PS/2 mode, this input indicates whether a
second drive is connected; DRV2 should be
low if a second drive is connected. This
status is reflected in a read of Status
Register A. (Only available in
FDC37C665GT. This pin must not be
driven in the FDC37C666GT)

Optional I/O port address decode output.
Refer to Configuration registers CR3, CR8
and CR9 for more information. Active low.
(Available in FDC37C665GT and
FDC37C666GT.) Defaults to tri-state after
power-up. This pin has a 30

a internal pull-

up.

This interrupt from the Parallel Port is
enabled/disabled via bit 4 of the Parallel
Port Control Register. Refer to
configuration registers CR1 and CR3 for
more information.

FDC37C666GT (Adapter Mode): Enhanced
Parallel Port mode select. Refer to
FDC37C666GT hardware configuration for
more information. Read and latched during
reset active.

PARALLEL PORT INTERFACE

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

nPrinter Select
Input

nSLCTIN

OD24

This active low output selects the printer.
This is the complement of bit 3 of the Printer
Control Register.

0P24

Refer to Parallel Port description for use of
this pin in ECP and EPP mode.

nInitiate Output

nINIT

OD24

This output is bit 2 of the printer control
register. This is used to initiate the printer
when low.

0P24

Refer to Parallel Port description for use of
this pin in ECP and EPP mode.

nAutofeed
Output

nAUTOFD

OD24

This output goes low to cause the printer to
automatically feed one line after each line is
printed. The nAUTOFD output is the
complement of bit 1 of the Printer Control
Register.

0P24

Refer to Parallel Port description for use of
this pin in ECP and EPP mode.

nStrobe Output

nSTROBE

OD24

An active low pulse on this output is used to
strobe the printer data into the printer. The
nSTROBE output is the complement of bit 0
of the Printer Control Register.

0P24

Refer to Parallel Port description for use of
this pin in ECP and EPP mode.

Busy

BUSY

This is a status output from the printer, a
high indicating that the printer is not ready
to receive new data. Bit 7 of the Printer
Status Register is the complement of the
BUSY input. Refer to Parallel Port
description for use of this pin in ECP and
EPP mode.

nAcknowledge

nACK

A low active output from the printer
indicating that it has received the data and
is ready to accept new data. Bit 6 of the
Printer Status Register reads the nACK
input. Refer to Parallel Port description for
use of this pin in ECP and EPP mode.

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

Paper End

Another status output from the printer, a
high indicating that the printer is out of
paper. Bit 5 of the Printer Status Register
reads the PE input. Refer to Parallel Port
description for use of this pin in ECP and
EPP mode.

Printer Selected
Status

SLCT

This high active output from the printer
indicates that it has power on. Bit 4 of the
Printer Status Register reads the SLCT
input. Refer to Parallel Port description for
use of this pin in ECP and EPP mode.

nError

nERR

A low on this input from the printer indicates
that there is a error condition at the printer.
Bit 3 of the Printer Status register reads the
nERR input. Refer to Parallel Port
description for use of this pin in ECP and
EPP mode.

71-68
66-63

Port Data

PD0-PD7

I/OP24

The bi-directional parallel data bus is used
to transfer information between CPU and
peripherals.

100

IOCHRDY

OD24P

In EPP mode, this pin is pulled low to
extend the read/write command. This pin
has an internal pull-up.

IDE

nIDE Low Byte
Enable

nIDEENLO

S1CF1

This active low signal is used in both the XT
and AT mode. In the AT mode, this pin is
active when the IDE is enabled and the I/O
address is accessing 1F0H-1F7H and
3F6H-3F7H in primary address mode or
170H-177H and 376H,377H in secondary
address mode. In the XT mode, this signal
is active for accessing 320H-323H, 8 bit
programmed I/O or DMA.

FDC37C666GT (Adapter Mode): Primary
Serial Configuration 1. Read and latched
during reset active to select the address of
the Secondary Serial Port.

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

nIDE High Byte
Enable

nIDEENHI

S1CF0

This signal is active low only in the AT
mode, and when IO16CSB is also active.
The I/O addresses for which this pin reacts
are 1F0H-1F7H in primary address mode or
170H-177H in secondary address mode.
This pin is not used in XT mode.

FDC37C666GT (Adapter Mode): Primary
Serial Configuration 0. Read and latched
during reset active to define the address of
the Secondary Serial Port.

nHard Disk Chip
Select

nHDCS0

IDEACF

O24

This is the Hard Disk Chip select
corresponding to addresses 1F0H-1F7H in
primary address mode or 170H-177H in
secondary address mode in the AT mode
and addresses 320H-323H in the XT mode.

FDC37C666GT (Adapter Mode): IDE
Address Control. Refer to FDC37C666GT
hardware configuration for more
information. Read and latched during
reset active.

nHard Disk Chip
Select

nHDCS1

FACF

O24

This is the Hard Disk Chip select
corresponding to 3F6H,3F7H for primary
address mode or 376H,377H for secondary
address mode in the AT mode and
addresses 3F6H,3F7H in the XT mode.

FDC37C666GT (Adapter Mode): Floppy
Disk Address Control. Refer to
FDC37C666GT hardware configuration for
more information. Read and latched during
reset active.

nI/O 16 Bit
Indicator

nIOCS16

nHDACK

This input indicates, in AT mode only, when
16 bit transfers are to take place. This
signal is generated by the hard disk
interface. Logic "0" = 16 bit mode; logic "1"
= 8 bit mode.

In the XT mode, this is the Hard Disk
Controller DMA Acknowledge, low active.

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

IDE Data Bit 7

IDED7

I/O24

IDE data bit 7 in the AT mode. IDED7
transfers data at I/O addresses 1F0H-1F7H
(R/W), 3F6 (R/W), 3F7(W). IDED7 should
be connected to IDE data bit 7. The
FDC37C665GT functions as a buffer
transferring data bit 7 between the IDE
device and the host. During I/O read of
3F7H, IDED7 is the FDC disk change bit. In
the XT mode, IDE7 is not used.

MISCELLANEOUS

Power Good

PWRGD

FDC37C665GT (Motherboard Mode): This
input indicates that the power (V

) is valid.

For device operation, PWRGD must be
active. When PWRGD is inactive, all inputs
to the FDC37C665GT are disconnected and
put in a low power mode, all outputs are put
into high impedance. The contents of all
registers are preserved as long as V

has a

valid value. The driver current drain in this
mode drops to ISTBY - standby current.
This input has a weak pullup resistor to V

nGame Port
Chip Select

nGAMECS

PADCF

FDC37C666GT (Adapter Mode): This is the
Game Port Chip Select output - active low.
It will go active when the I/O address is
201H.

FDC37C666GT (Adapter Mode): Parallel
Port Mode Control. Refer to FDC37C666GT
hardware configuration for more
information. Read and latched during reset
active.

CLOCK 1

X1/CLK1

ICLK

The external connection for a parallel
resonant 24 MHz crystal. A CMOS
compatible oscillator is required if crystal is
not used.

CLOCK 2

X2/CLK2

OCLK

24 MHz crystal. If an external clock is used,
this pin should not be connected. This pin
should not be used to drive any other
drivers.

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

15,72

Power

+ 5 Volt supply pin.

6,47,

67,95

Ground

GND

Ground pin.

Note 1: These active low open drain outputs select motor drives 0-3. In non-ECP modes, four drives

can be supported directly. These motor enable bits are controlled by software via the Digital
Output Register (DOR). In ECP mode, MTR0,1 can be used to directly support 2 drives or
can support 4 drives by using an external 2 to 4 decoder.

Note 2: Active low open drain outputs select drives 0-3. In non-ECP modes, four drives can be

supported directly. These drive select outputs are a decode of bits 0 and 1 of the Digital
Output Register and qualified by the appropriate Motor Enable Bit of the DOR (bits 4-7). In
ECP mode, DS0,1 can be used to directly support 2 drives or can support 4 drives by using
an external 2 to 4 decoder.

FIGURE 1 - FDC37C665GT/FDC37C666GT BLOCK DIAGRAM

nDSR1, nDCD1,
nRI1, nDTR1

TXD1, nCTS1, nRTS1

nINIT, nAUTOFD

MULTI-MODE

PARALLEL
PORT/FDC

MUX

16C550

COMPATIBLE

SERIAL
PORT 1

16C550

COMPATIBLE

SERIAL
PORT 2

IDE

CONFIGURATION

REGISTERS

DECODER

POWER

MANAGEMENT

INTERFACE

CONTROL BUS

ADDRESS BUS

DATA BUS

CLOCK

GEN

SERIAL

CLOCK CLK 1 CLK2

nINDEX

nTRK0

nDSKCHG

nWRPRT

nWGATE

DENSEL

nDIR

nSTEP

DRATE0

DRATE1

nHDSEL

nDS0,1,2,3

nMTR0,1,2,3

RDATA

RCLOCK

WDATA

WCLOCK

nWDATA nRDATA

nIDEENLO, nIDEENHI

nHDCS0, nHDCS1

nIOCS16

TXD2, nCTS2, nRTS2

RXD2

nDSR2, nDCD2,
nRI2, nDTR2

IDED7

RXD1

PD0-7

BUSY, SLCT, PE,

nERROR, nACK

nSTROBE, nSLCTIN,

nGAMECS

PWRGD

(FDC37C665GT only)

(FDC37C666GT only)

Vcc (2)

Vss (4)

SMSC

PROPRIETARY

82077 COMPATIBLE

VERTICAL

FLOPPYDISK

CONTROLLER

CORE

DIGITAL

DATA

SEPARATOR
WITH WRITE

PRECOM-

PENSATION

PDIR

HOST

CPU

INTERFACE

nIOR

nIOW

AEN

A0-A9

DO-D7

FDRQ

nDACK

IRQ3

IRQ4

PINTR

FINTR

RESET

PDRQ

PDACK

A10

IOCHRDY

PINTR2

FUNCTIONAL DESCRIPTION

SUPER I/O REGISTERS

The address map, shown below in Table 1,
shows the addresses of the different blocks of
the Super I/O immediately after power up. The
base addresses of the FDC, IDE, serial and
parallel ports can be moved via the
configuration registers. Some addresses are
used to access more than one register.

HOST PROCESSOR INTERFACE

The host processor communicates with the
FDC37C665GT/666GT through a series of
read/write registers. The port addresses for
these registers are shown in Table 1. Register
access is accomplished through programmed
I/O or DMA transfers. All registers are 8 bits
wide except the IDE data register at port 1F0H
which is 16 bits wide. All host interface output
buffers are capable of sinking a minimum of 24
mA.

Table 1 - FDC37C665GT/666GT Block Addresses

ADDRESS

BLOCK NAME

NOTES

3F0, 3F1

Configuration

Write only; Note 1, 2

3F0, 3F1

Floppy Disk

Read only; Address at power
up; Note 2

3F2, 3F3, 3F4, 3F5, 3F7

Floppy Disk

Address at power up; Note 2

3F8-3FF

Serial Port Com 1

Address at power up; Note 2

2F8-2FF

Serial Port Com 2

Address at power up; Note 2

278-27A

Parallel Port

Address at power up; Note 2

1F0-1F7, 3F6, 3F7

IDE

AT Mode; Note 2, 3

Note 1: Configuration registers can only be modified in configuration mode, entered only by writing a

security code sequence to 3F0. The configuration registers can only be read in configuration
mode by accessing 3F1. Access to status registers A and B of the floppy disk is disabled in
configuration mode. Outside of configuration mode, a read of 3F0 accesses status register A
and a read of 3F1 accesses status register B of the floppy disk.

Note 2: Address at power up; These addresses can be changed in the configuration setup.
Note 3: Addresses 320H-323H and 3F5-3F7H for XT Mode. Selectable in configuration setup.

FLOPPY DISK CONTROLLER

The Floppy Disk Controller (FDC) provides the
interface between a host microprocessor and
the floppy disk drives. The FDC integrates the
functions of the Formatter/Controller, Digital
Data Separator, Write Precompensation and
Data Rate Selection logic for an IBM XT/AT
compatible FDC. The true CMOS 765B core
guarantees 100% IBM PC XT/AT compatibility
in addition to providing data overflow and
underflow protection.

The FDC37C665GT and FDC37C666GT are
compatible to the 82077AA using SMSC's
proprietary floppy disk controller core.

FLOPPY DISK CONTROLLER INTERNAL
REGISTERS

The Floppy Disk Controller contains eight
internal registers which facilitate the interfacing
between the host microprocessor and the disk
drive. Table 2 shows the addresses required to
access these registers. Registers other than the
ones shown are not supported. The rest of the
description assumes that the primary addresses
have been selected.

Table 2 - Status, Data and Control Registers

PRIMARY

ADDRESS

SECONDARY

ADDRESS

REGISTER

3F0
3F1
3F2
3F3
3F4
3F4
3F5
3F6
3F7
3F7

370
371
372
373
374
374
375
376
377
377

R
R

R/W
R/W

R/W

Status Register A
Status Register B
Digital Output Register
Tape Drive Register
Main Status Register
Data Rate Select Register
Data (FIFO)
Reserved
Digital Input Register
Configuration Control Register

SRA
SRB

DOR

TSR

MSR

DSR

FIFO

DIR

CCR

For information on the floppy disk on Parallel Port pins, refer to Configuration Register CR4
and Parallel Port Floppy Disk Controller description.

STATUS REGISTER A (SRA)

Address 3F0 READ ONLY
This register is read-only and monitors the state
of the FINTR pin and several disk interface pins,

in PS/2 and Model 30 modes. The SRA can be
accessed at any time when in PS/2 mode. In
the PC/AT mode the data bus pins D0 - D7 are
held in a high impedance state for a read of
address 3F0.

PS/2 Mode

BIT 0 DIRECTION
Active high status indicating the direction of
head movement. A logic "1" indicating inward
direction a logic "0" outward.

BIT 1 nWRITE PROTECT
Active low status of the WRITE PROTECT disk
interface input. A logic "0" indicating that the
disk is write protected.

BIT 2 nINDEX
Active low status of the INDEX disk interface
input.

BIT 3 HEAD SELECT
Active high status of the HDSEL disk interface
input. A logic "1" selects side 1 and a logic "0"
selects side 0.

BIT 4 nTRACK 0
Active low status of the TRK0 disk interface
input.

BIT 5 STEP
Active high status of the STEP output disk
interface output pin.

BIT 6 nDRV2
Active low status of the DRV2 disk interface
input pin, indicating that a second drive has
been installed.

BIT 7 INTERRUPT PENDING
Active high bit indicating the state of the Floppy
Disk Interrupt output.

INT

PENDING

nDRV2

STEP

nTRK0 HDSEL nINDX

nWP

DIR

RESET

COND.

N/A

PS/2 Model 30 Mode

BIT 0 nDIRECTION
Active low status indicating the direction of head
movement. A logic "0" indicating inward
direction a logic "1" outward.

BIT 1 WRITE PROTECT
Active high status of the WRITE PROTECT disk
interface input. A logic "1" indicating that the
disk is write protected.

BIT 2 INDEX
Active high status of the INDEX disk interface
input.

BIT 3 nHEAD SELECT
Active low status of the HDSEL disk interface
input. A logic "0" selects side 1 and a logic "1"
selects side 0.

BIT 4 TRACK 0
Active high status of the TRK0 disk interface
input.

BIT 5 STEP
Active high status of the latched STEP disk
interface output pin. This bit is latched with the
STEP output going active, and is cleared with a
read from the DIR register, or with a hardware
or software reset.

BIT 6 DMA REQUEST
Active high status of the DRQ output pin.

BIT 7 INTERRUPT PENDING
Active high bit indicating the state of the Floppy
Disk Interrupt output.

INT

PENDING

DRQ

STEP

F/F

TRK0

nHDSEL

INDX

nDIR

RESET

COND.

N/A

STATUS REGISTER B (SRB)

Address 3F1 READ ONLY
This register is read-only and monitors the state
of several disk interface pins, in PS/2 and Model

30 modes. The SRB can be accessed at any
time when in PS/2 mode. In the PC/AT mode
the data bus pins D0 - D7 are held in a high
impedance state for a read of address 3F1.

PS/2 Mode

BIT 0 MOTOR ENABLE 0
Active high status of the MTR0 disk interface
output pin. This bit is low after a hardware reset
and unaffected by a software reset.

BIT 1 MOTOR ENABLE 1
Active high status of the MTR1 disk interface
output pin. This bit is low after a hardware reset
and unaffected by a software reset.

BIT 2 WRITE GATE
Active high status of the WGATE disk interface
output.

BIT 3 READ DATA TOGGLE
Every inactive edge of the RDATA input causes
this bit to change state.

BIT 4 WRITE DATA TOGGLE
Every inactive edge of the WDATA input causes
this bit to change state.

BIT 5 DRIVE SELECT 0
Reflects the status of the Drive Select 0 bit of
the DOR (address 3F2 bit 0). This bit is cleared
after a hardware reset, it is unaffected by a
software reset.

BIT 6 RESERVED
Always read as a logic "1".

BIT 7 RESERVED
Always read as a logic "1".

DRIVE

SEL0

WDATA

TOGGLE

RDATA

TOGGLE

WGATE

MOT

EN1

MOT

EN0

RESET

COND.

PS/2 Model 30 Mode

BIT 0 nDRIVE SELECT 2
Active low status of the DS2 disk interface
output.

BIT 1 nDRIVE SELECT 3
Active low status of the DS3 disk interface
output.

BIT 2 WRITE GATE
Active high status of the latched WGATE output
signal. This bit is latched by the active going
edge of WGATE and is cleared by the read of
the DIR register.

BIT 3 READ DATA
Active high status of the latched RDATA output
signal. This bit is latched by the inactive going
edge of RDATA and is cleared by the read of the
DIR register.

BIT 4 WRITE DATA
Active high status of the latched WDATA output
signal. This bit is latched by the inactive going
edge of WDATA and is cleared by the read of
the DIR register. This bit is not gated with
WGATE.

BIT 5 nDRIVE SELECT 0
Active low status of the DS0 disk interface
output.

BIT 6 nDRIVE SELECT 1
Active low status of the DS1 disk interface
output.

BIT 7 nDRV2
Active low status of the DRV2 disk interface
input.

nDRV2

nDS1

nDS0

WDATA

F/F

RDATA

F/F

WGATE

F/F

nDS3

nDS2

RESET

COND.

N/A

DIGITAL OUTPUT REGISTER (DOR)

Address 3F2 READ/WRITE
The DOR controls the drive select and motor
enables of the disk interface outputs. It also

contains the enable for the DMA logic and
contains a software reset bit. The contents of
the DOR are unaffected by a software reset.
The DOR can be written to at any time.

BIT 0 and 1 DRIVE SELECT
These two bits a are binary encoded for the four
drive selects DS0-DS3, thereby allowing only
one drive to be selected at a time.

BIT 2 nRESET
A logic "0" written to this bit resets the Floppy
disk controller. This reset will remain active
until a logic "1" is written to this bit. This
software reset does not affect the DSR and CCR
registers, nor does it affect the other bits of the
DOR register. The minimum reset duration
required is 100ns, therefore toggling this bit by
consecutive writes to this register is a valid
method of issuing a software reset.

BIT 3 DMAEN
PC/AT and Model 30 Mode:
Writing this bit to logic "1" will enable the DRQ,
nDACK, TC and FINTR outputs. This bit being
a logic "0" will disable the nDACK and TC
inputs, and hold the DRQ and FINTR outputs in
a high impedance state. This bit is a logic "0"
after a reset and in these modes.

PS/2 Mode: In this mode the DRQ, nDACK, TC
and FINTR pins are always enabled. During a
reset, the DRQ, nDACK, TC, and FINTR pins
will remain enabled, but this bit will be cleared to
a logic "0".

BIT 4 MOTOR ENABLE 0
This bit controls the MTR0 disk interface output.
A logic "1" in this bit will cause the output pin to
go active.

BIT 5 MOTOR ENABLE 1
This bit controls the MTR1 disk interface output.
A logic "1" in this bit will cause the output pin to
go active.

BIT 6 MOTOR ENABLE 2
This bit controls the MTR2 disk interface output.
A logic "1" in this bit will cause the output pin to
go active.

BIT 7 MOTOR ENABLE 3
This bit controls the MTR3 disk interface output.
A logic "1" in this bit causes the output to go
active.

Table 3 - Drive Activation Values

MOT

EN3

MOT

EN2

MOT

EN1

MOT

EN0

DMAEN nRESE

DRIVE

SEL1

DRIVE

SEL0

RESET

COND.

DRIVE

DOR VALUE

0
1
2
3

1CH
2DH
4EH

8FH

TAPE DRIVE REGISTER (TDR)

Address 3F3 READ/WRITE

This register is included for 82077 software
compatability. The robust digital data separator
used in the FDC37C665GT does not require its
characteristics modified for tape support. The
contents of this register are not used internal to
the device. The TDR is unaffected by a
software reset. Bits 2-7 are tri-stated when
read in this mode.

Table 4- Tape Select Bits

Table 5 - Internal 4 Drive Decode - Normal

DIGITAL OUTPUT REGISTER

DRIVE SELECT OUTPUTS

(ACTIVE LOW)

MOTOR ON OUTPUTS

(ACTIVE LOW)

Bit 7

Bit 6

Bit 5

Bit 4

Bit1

Bit 0

nDS3

nDS2

nDS1

nDS0

nMTR3

nMTR2

nMTR1

nMTR0

nBIT 7

nBIT 6

nBIT 5

nBIT 4

nBIT 7

nBIT 6

nBIT 5

nBIT 4

nBIT 7

nBIT 6

nBIT 5

nBIT 4

nBIT 7

nBIT 6

nBIT 5

nBIT 4

nBIT 7

nBIT 6

nBIT 5

nBIT 4

Table 6 - Internal 4 Drive Decode - Drives 0 and 1 Swapped

DIGITAL OUTPUT REGISTER

DRIVE SELECT OUTPUTS

(ACTIVE LOW)

MOTOR ON OUTPUTS

(ACTIVE LOW)

Bit 7

Bit 6

Bit 5

Bit 4

Bit1

Bit 0

nDS3

nDS2

nDS1

nDS0

nMTR3

nMTR2

nMTR1

nMTR0

nBIT 7

nBIT 6

nBIT 4

nBIT 5

nBIT 7

nBIT 6

nBIT 4

nBIT 5

nBIT 7

nBIT 6

nBIT 4

nBIT 5

nBIT 7

nBIT 6

nBIT 4

nBIT 5

nBIT 7

nBIT 6

nBIT 4

nBIT 5

TAPE SEL1

TAPE SEL2

DRIVE

SELECTED

0
0
1
1

0
1
0
1

None

1
2
3

Table 7 - External 2 to 4 Drive Decode - Normal

DIGITAL OUTPUT REGISTER

DRIVE SELECT

OUTPUTS

(ACTIVE LOW)

MOTOR ON OUTPUTS

(ACTIVE LOW)

Bit 7

Bit 6

Bit 5

Bit 4

Bit1

Bit 0

nDS1

nDS0

nMTR1

nMTR0

Table 8 - External 2 to 4 Drive Decode - Drives 0 and 1 Swapped

DIGITAL OUTPUT REGISTER

DRIVE SELECT

OUTPUTS

(ACTIVE LOW)

MOTOR ON OUTPUTS

(ACTIVE LOW)

Bit 7

Bit 6

Bit 5

Bit 4

Bit1

Bit 0

nDS1

nDS0

nMTR1

nMTR0

Normal Floppy Mode

Normal mode. Register 3F3 contains only bits 0 and 1. When this register is read, bits 2 - 7 are a
high impedance.

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

REG 3F3

Tri-state

tape sel1

tape sel0

Enhanced Floppy Mode 2 (OS2)

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

REG 3F3

Media

ID1

Media

ID0

Drive Type ID

Floppy Boot Drive

tape sel1

tape sel0

For this mode, DRATE0 and DRATE1 pins are
inputs, and these inputs are gated into bits 6
and 7 of the 3F3 register. These two bits are
not affected by a hard or soft reset.

BIT 7 MEDIA ID 1 READ ONLY (Pin 18) (See
Table 9)

BIT 6 MEDIA ID 0 READ ONLY (Pin 19) (See
Table 10)

BITS 5 and 4 Drive Type ID - These Bits reflect
two of the bits of configuration register 6.

Which two bits depends on the last drive
selected in the Digital Output Register (3F2).
(See Table 11)

BITS 3 and 2 Floppy Boot Drive - These bits
reflect the value of configuration register 7 bits
1, 0. Bit 3 = CR7 Bit DB1. Bit 2 = CR7 Bit DB0.

Bits 1 and 0 - Tape Drive Select
(READ/WRITE). Same as in Normal and
Enhanced Floppy Mode. 1.

Table 9 - Media ID1

DRATE1

Input

MEDIA ID1

BIT 7

Pin 18

CR7-DB3 = 0

CR7-DB3 = 1

Table 10 - Media ID0

DRATE0

Input

MEDIA ID0

BIT 6

Pin 19

CR7-DB2 = 0

CR7-DB2 = 1

DATA RATE SELECT REGISTER (DSR)

Address 3F4 WRITE ONLY
This register is write only. It is used to program
the data rate, amount of write precompensation,
power down status, and software reset. The
data rate is programmed using the
Configuration Control Register (CCR) not the
DSR, for PC/AT and PS/2 Model 30 and

Microchannel applications. Other applications
can set the data rate in the DSR. The data rate
of the floppy controller is the most recent write
of either the DSR or CCR. The DSR is
unaffected by a software reset. A hardware
reset will set the DSR to 02H, which
corresponds to the default precompensation
setting and 250kb/s.

BIT 0 and 1 DATA RATE SELECT
These bits control the data rate of the floppy
controller. See Table 13 for the settings
corresponding to the individual data rates. The
data rate select bits are unaffected by a
software reset, and are set to 250kb/s after a
hardware reset.

BIT 2 through 4 PRECOMPENSATION
SELECT
These three bits select the value of write
precompensation that will be applied to the
WDATA output signal. Table 12 shows the
precompensation values for the combination of
these bits settings. Track 0 is the default
starting track number to start precompensation.
this starting track number can be changed by
the configure command.

BIT 5 UNDEFINED
Should be written as a logic "0".

BIT 6 LOW POWER
A logic "1" written to this bit will put the floppy
controller into Manual Low Power mode. The

floppy controller clock and data separator
circuits will be turned off. The controller will
come out of manual low power mode after a
software reset or access to the Data Register or
Main Status Register.

BIT 7 SOFTWARE RESET
This active high bit has the same function as the
DOR RESET (DOR bit 2) except that this bit is
self clearing.

Table 12 - Precompensation Delays

S/W

RESET

POWER

DOWN

PRE-

COMP2

PRE-

COMP1

PRE-

COMP0

DRATE

SEL1

DRATE

SEL0

RESET

COND.

PRECOMP

432

PRECOMPENSATION

DELAY

111
001
010
011
100
101
110
000

0.00 ns-DISABLED

41.67 ns
83.34 ns

125.00 ns
166.67 ns
208.33 ns
250.00 ns

Default (See Table 14)

Table 13 - Data Rates

Table 14 - Default Precompensation Delays

MAIN STATUS REGISTER

Address 3F4 READ ONLY
The Main Status Register is a read-only register
and indicates the status of the disk controller.
The Main Status Register can be read at any

time. The MSR indicates when the disk
controller is ready to receive data via the Data
Register. It should be read before each byte
transferring to or from the data register except in
DMA mode. NO delay is required when reading
the MSR after a data transfer.

BIT 0 - 3 DRV x BUSY
These bits are set to 1s when a drive is in the
seek portion of a command, including implied
and overlapped seeks and recalibrates.

BIT 4 COMMAND BUSY
This bit is set to a 1 when a command is in
progress. This bit will go active after the
command byte has been accepted and goes
inactive at the end of the results phase. If there
is no result phase (Seek, Recalibrate
commands), this bit is returned to a 0 after the
last command byte.

BIT 5 NON-DMA
This mode is selected in the SPECIFY
command and will be set to a 1 during the
execution phase of a command. This is for
polled data transfers and helps differentiate
between the data transfer phase and the reading
of result bytes.

BIT 6 DIO
Indicates the direction of a data transfer once a
RQM is set. A 1 indicates a read and a 0
indicates a write is required.

BIT 7 RQM
Indicates that the host can transfer data if set to
a 1. No access is permitted if set to a 0.

DRATESEL

DATA RATE

MFM

1
0
0
1

1
0
1
0

1 Mbps

500 Kbps
300 Kbps
250 Kbps

Illegal

250 Kbps
150 Kbps
125 Kbps

DATA RATE

PRECOMPENSATION

DELAYS

1 Mbps

500 Kbps
300 Kbps
250 Kbps

41.67 ns

125 ns
125 ns
125 ns

RQM

DIO

NON
DMA

CMD

BUSY

DRV3
BUSY

DRV2
BUSY

DRV1
BUSY

DRV0
BUSY

DATA REGISTER (FIFO)

Address 3F5 READ/WRITE
All command parameter information, disk data
and result status are transferred between the
host processor and the floppy disk controller
through the Data Register.

Data transfers are governed by the RQM and
DIO bits in the Main Status Register.

The Data Register defaults to FIFO disabled
mode after any form of reset. This maintains
PC/AT hardware compatibility. The default
values can be changed through the Configure
command (enable full FIFO operation with
threshold control). The advantage of the FIFO
is that it allows the system a larger DMA
latency without causing a disk error. Table 15
gives several examples of the delays with a

FIFO. The data is based upon the following
formula:

At the start of a command, the FIFO action is
always disabled and command parameters
must be sent based upon the RQM and DIO bit
settings. As the command execution phase is
entered, the FIFO is cleared of any data to
ensure that invalid data is not transferred.

An overrun or underrun will terminate the
current command and the transfer of data. Disk
writes will complete the current sector by
generating a 00 pattern and valid CRC. Reads
require the host to remove the remaining data
so that the result phase may be entered.

Table 15 - FIFO Service Delay

FIFO THRESHOLD

EXAMPLES

MAXIMUM DELAY TO SERVICING

AT 1 Mbps DATA RATE

1 byte

2 bytes
8 bytes

15 bytes

1 x 8

s - 1.5

s = 6.5

2 x 8

s - 1.5

s = 14.5

8 x 8

s - 1.5

s = 62.5

15 x 8

s - 1.5

s = 118.5

FIFO THRESHOLD

EXAMPLES

MAXIMUM DELAY TO SERVICING

AT 500 Kbps DATA RATE

1 byte

2 bytes
8 bytes

15 bytes

1 x 16

s - 1.5

s = 14.5

2 x 16

s - 1.5

s = 30.5

8 x 16

s - 1.5

s = 126.5

15 x 16

s - 1.5

s = 238.5

Threshold # x

DATA RATE

x 8

- 1.5

s = DELAY

DIGITAL INPUT REGISTER (DIR)

Address 3F7 READ ONLY
This register is read-only in all modes.

PC-AT Mode

BIT 0 - 6 UNDEFINED
The data bus outputs D0 - 6 will remain in a
high impedance state during a read of this
register.

BIT 7 DSKCHG
This bit monitors the pin of the same name and
reflects the opposite value seen on the disk
cable.

PS/2 Mode

BIT 0 nHIGH DENS
This bit is low whenever the 500 Kbps or 1 Mbps
data rates are selected, and high when 250Kbps
and 300Kbps are selected.

BITS 1 - 2 DATA RATE SELECT
These bits control the data rate of the floppy
controller. See Table 13 for the settings
corresponding to the individual data rates. The
data rate select bits are unaffected by a

software reset, and are set to 250kb/s after a
hardware reset.

BITS 3 - 6 UNDEFINED
Always read as a logic "1"

BIT 7 DSKCHG
This bit monitors the pin of the same name and
reflects the opposite value seen on the disk
cable.

DSK

CHG

RESET

COND.

N/A

DSK

CHG

DRATE

SEL1

DRATE

SEL0

nHIGH

DENS

RESET

COND.

N/A

Model 30 Mode

BITS 0 - 1 DATA RATE SELECT
These bits control the data rate of the floppy
controller. See Table 13 for the settings
corresponding to the individual data rates. The
data rate select bits are unaffected by a
software reset, and are set to 250kb/s after a
hardware reset.

BIT 2 NOPREC
This bit reflects the value of NOPREC bit set in
the CCR register.

BIT 3 DMAEN
This bit reflects the value of DMAEN bit set in
the DOR register bit 3.

BITS 4 - 6 UNDEFINED
Always read as a logic "0"

BIT 7 DSKCHG
This bit monitors the pin of the same name and
reflects the opposite value seen on the pin.

DSK

CHG

DMAEN NOPREC DRATE

SEL1

DRATE

SEL0

RESET

COND.

N/A

CONFIGURATION CONTROL REGISTER (CCR)

Address 3F7 WRITE ONLY
PC/AT and PS/2 Modes

BIT 0 and 1 DATA RATE SELECT 0 and 1
These bits determine the data rate of the floppy
controller. See Table 13 for the appropriate
values.

BIT 2 - 7 RESERVED
Should be set to a logical "0"

PS/2 Model 30 Mode

BIT 0 and 1 DATA RATE SELECT 0 and 1
These bits determine the data rate of the floppy
controller. See Table 13 for the appropriate
values.

BIT 2 NO PRECOMPENSATION
This bit can be set by software, but it has no
functionality. It can be read by bit 2 of the DSR
when in Model 30 register mode. Unaffected by
software reset.

BIT 3 - 7 RESERVED
Should be set to a logical "0"

Table 16 shows the state of the DENSEL pin.
The DENSEL pin is set high after a hardware
reset and is unaffected by the DOR and the
DSR resets.

Table 16 - DENSEL Encoding

DRATE

SEL1

DRATE

SEL0

RESET

COND.

N/A

NOPREC DRATE

SEL1

DRATE

SEL0

RESET

COND.

N/A

Data Rate

IDENT

DENSEL

1Mbps

500kbps

300kps

250kbps

STATUS REGISTER ENCODING

During the Result Phase of certain commands, the Data Register contains data bytes that give the
status of the command just executed.

Table 17 - Status Register 0

BIT NO.

SYMBOL

NAME

DESCRIPTION

7,6

Interrupt
Code

00 - Normal termination of command. The specified
command was properly executed and completed
without error.
01 - Abnormal termination of command. Command
execution was started, but was not successfully
completed.
10 - Invalid command. The requested command
could not be executed.
11 - Abnormal termination caused by Polling.

Seek End

The FDC completed a Seek, Relative Seek or
Recalibrate command (used during a Sense Interrupt
Command).

Equipment
Check

The TRK0 pin failed to become a "1" after:
1.

80 step pulses in the Recalibrate command.

The Relative Seek command caused the FDC to
step outward beyond Track 0.

Unused. This bit is always "0".

Head
Address

The current head address.

1,0

DS1,0

Drive Select

The current selected drive.

Table 18 - Status Register 1

BIT NO.

SYMBOL

NAME

DESCRIPTION

End of
Cylinder

The FDC tried to access a sector beyond the final
sector of the track (255D). Will be set if TC is not
issued after Read or Write Data command.

Unused. This bit is always "0".

Data Error

The FDC detected a CRC error in either the ID field or
the data field of a sector.

Overrun/
Underrun

Becomes set if the FDC does not receive CPU or DMA
service within the required time interval, resulting in
data overrun or underrun.

Unused. This bit is always "0".

No Data

Any one of the following:
1.

Read Data, Read Deleted Data command - the

FDC did not find the specified sector.

Read ID command - the FDC cannot read the ID

field without an error.

Read A Track command - the FDC cannot find

the proper sector sequence.

Not Writable

WP pin became a "1" while the FDC is executing a
Write Data, Write Deleted Data, or Format A Track
command.

Missing
Address Mark

Any one of the following:
1.

The FDC did not detect an ID address mark at the

specified track after encountering the index pulse
from the IDX pin twice.

The FDC cannot detect a data address mark or a

deleted data address mark on the specified track.

Table 19 - Status Register 2

BIT NO.

SYMBOL

NAME

DESCRIPTION

Unused. This bit is always "0".

Control Mark

Any one of the following:
1.

Read Data command - the FDC encountered a

deleted data address mark.

Read Deleted Data command - the FDC

encountered a data address mark.

Data Error in
Data Field

The FDC detected a CRC error in the data field.

Wrong
Cylinder

The track address from the sector ID field is different
from the track address maintained inside the FDC.

Unused. This bit is always "0".

Bad Cylinder

The track address from the sector ID field is different
from the track address maintained inside the FDC and
is equal to FF hex, which indicates a bad track with a
hard error according to the IBM soft-sectored format.

Missing Data
Address Mark

The FDC cannot detect a data address mark or a
deleted data address mark.

Table 20- Status Register 3

BIT NO.

SYMBOL

NAME

DESCRIPTION

Unused. This bit is always "0".

Write
Protected

Indicates the status of the WP pin.

Unused. This bit is always "1".

Track 0

Indicates the status of the TRK0 pin.

Unused. This bit is always "1".

Head
Address

Indicates the status of the HDSEL pin.

1,0

DS1,0

Drive Select

Indicates the status of the DS1, DS0 pins.

RESET

There are three sources of system reset on the
FDC: the RESET pin of the FDC37C665GT, a
reset generated via a bit in the DOR, and a reset
generated via a bit in the DSR. At power on, a
Power On Reset initializes the FDC. All resets
take the FDC out of the power down state.

All operations are terminated upon a RESET,
and the FDC enters an idle state. A reset while
a disk write is in progress will corrupt the data
and CRC.

On exiting the reset state, various internal
registers are cleared, including the Configure
command information, and the FDC waits for a
new command. Drive polling will start unless
disabled by a new Configure command.

RESET Pin (Hardware Reset)

The RESET pin is a global reset and clears all
registers except those programmed by the
Specify command. The DOR reset bit is
enabled and must be cleared by the host to exit
the reset state.

DOR Reset vs. DSR Reset (Software Reset)

These two resets are functionally the same.
Both will reset the FDC core, which affects drive
status information and the FIFO circuits. The
DSR reset clears itself automatically while the
DOR reset requires the host to manually clear it.
DOR reset has precedence over the DSR reset.
The DOR reset is set automatically upon a pin
reset. The user must manually clear this reset
bit in the DOR to exit the reset state.

MODES OF OPERATION

The FDC has three modes of operation, PC/AT
mode, PS/2 mode and Model 30 mode. These
are determined by the state of the IDENT and
MFM bits 6 and 5 respectively of configuration
register 3.

PC/AT mode - (IDENT high, MFM a "don't
care")
The PC/AT register set is enabled, the DMA
enable bit of the DOR becomes valid (FINTR
and DRQ can be hi Z), and TC and DENSEL
become active high signals.

PS/2 mode - (IDENT low, MFM high)
This mode supports the PS/2 models 50/60/80
configuration and register set. The DMA bit of
the DOR becomes a "don't care", (FINTR and
DRQ are always valid), TC and DENSEL
become active low.

Model 30 mode - (IDENT low, MFM low)
This mode supports PS/2 Model 30
configuration and register set. The DMA enable
bit of ther DOR becomes valid (FINTR and DRQ
can be hi Z), TC is active high and DENSEL is
active low.

DMA TRANSFERS

DMA transfers are enabled with the Specify
command and are initiated by the FDC by
activating the FDRQ pin during a data transfer
command. The FIFO is enabled directly by
asserting nDACK and addresses need not be
valid.

Note that if the DMA controller (i.e. 8237A) is
programmed to function in verify mode, a
pseudo read is performed by the FDC based
only on nDACK. This mode is only available
when the FDC has been configured into byte
mode (FIFO disabled) and is programmed to do
a read. With the FIFO enabled, the FDC can
perform the above operation by using the new
Verify command; no DMA operation is needed.

CONTROLLER PHASES

For simplicity, command handling in the FDC
can be divided into three phases: Command,
Execution, and Result. Each phase is described
in the following sections.

Command Phase

After a reset, the FDC enters the command
phase and is ready to accept a command from
the host. For each of the commands, a defined

set of command code bytes and parameter
bytes has to be written to the FDC before the
command phase is complete. (Please refer to
Table 21 for the command set descriptions.)
These bytes of data must be transferred in the
order prescribed.

Before writing to the FDC, the host must
examine the RQM and DIO bits of the Main
Status Register. RQM and DIO must be equal
to "1" and "0" respectively before command
bytes may be written. RQM is set false by the
FDC after each write cycle until the received
byte is processed. The FDC asserts RQM again
to request each parameter byte of the command
unless an illegal command condition is
detected. After the last parameter byte is
received, RQM remains "0" and the FDC
automatically enters the next phase as defined
by the command definition.

The FIFO is disabled during the command
phase to provide for the proper handling of the
"Invalid Command" condition.

Execution Phase

All data transfers to or from the FDC occur
during the execution phase, which can proceed
in DMA or non-DMA mode as indicated in the
Specify command.

After a reset, the FIFO is disabled. Each data
byte is transferred by an FINT or FDRQ
depending on the DMA mode. The Configure
command can enable the FIFO and set the
FIFO threshold value.

The following paragraphs detail the operation of
the FIFO flow control. In these descriptions,
<threshold> is defined as the number of bytes
available to the FDC when service is requested
from the host and ranges from 1 to 16. The
parameter FIFOTHR, which the user programs,
is one less and ranges from 0 to 15.

A low threshold value (i.e. 2) results in longer
periods of time between service requests, but
requires faster servicing of the request for both
read and write cases. The host reads (writes)
from (to) the FIFO until empty (full), then the
transfer request goes inactive. The host must
be very responsive to the service request. This
is the desired case for use with a "fast" system.

A high value of threshold (i.e. 12) is used with a
"sluggish" system by affording a long latency
period after a service request, but results in
more frequent service requests.

Non-DMA Mode - Transfers from the FIFO to
the Host

The FINT pin and RQM bits in the Main Status
Register are activated when the FIFO contains
(16-<threshold>) bytes or the last bytes of a full
sector have been placed in the FIFO. The FINT
pin can be used for interrupt-driven systems,
and RQM can be used for polled systems. The
host must respond to the request by reading
data from the FIFO. This process is repeated
until the last byte is transferred out of the FIFO.
The FDC will deactivate the FINT pin and RQM
bit when the FIFO becomes empty.

Non-DMA Mode - Transfers from the Host to the
FIFO

The FINT pin and RQM bit in the Main Status
Register are activated upon entering the
execution phase of data transfer commands.
The host must respond to the request by writing
data into the FIFO. The FINT pin and RQM bit
remain true until the FIFO becomes full. They
are set true again when the FIFO has
<threshold> bytes remaining in the FIFO. The
FINT pin will also be deactivated if TC and
nDACK both go inactive. The FDC enters the
result phase after the last byte is taken by the
FDC from the FIFO (i.e. FIFO empty condition).

DMA Mode - Transfers from the FIFO to the
Host

The FDC activates the FDRQ pin when the FIFO
contains (16 - <threshold>) bytes, or the last
byte of a full sector transfer has been placed in
the FIFO. The DMA controller must respond to
the request by reading data from the FIFO. The
FDC will deactivate the FDRQ pin when the
FIFO becomes empty. FDRQ goes inactive
after nDACK goes active for the last byte of a
data transfer (or on the active edge of nIOR, on
the last byte, if no edge is present on nDACK).
A data underrun may occur if FDRQ is not
removed in time to prevent an unwanted cycle.

DMA Mode - Transfers from the Host to the
FIFO

The FDC activates the FDRQ pin when entering
the execution phase of the data transfer
commands. The DMA controller must respond
by activating the nDACK and nIOW pins and
placing data in the FIFO. FDRQ remains active
until the FIFO becomes full. FDRQ is again set
true when the FIFO has <threshold> bytes
remaining in the FIFO. The FDC will also
deactivate the FDRQ pin when TC becomes true
(qualified by nDACK), indicating that no more
data is required. FDRQ goes inactive after
nDACK goes active for the last byte of a data
transfer (or on the active edge of nIOW of the
last byte, if no edge is present on nDACK). A
data overrun may occur if FDRQ is not removed
in time to prevent an unwanted cycle.

Data Transfer Termination

The FDC supports terminal count explicitly
through the TC pin and implicitly through the
underrun/overrun and end-of-track (EOT)
functions. For full sector transfers, the EOT
parameter can define the last sector to be
transferred in a single or multi-sector transfer.

If the last sector to be transferred is a partial
sector, the host can stop transferring the data in
mid-sector, and the FDC will continue to
complete the sector as if a hardware TC was
received. The only difference between these
implicit functions and TC is that they return
"abnormal termination" result status. Such
status indications can be ignored if they were
expected.

Note that when the host is sending data to the
FIFO of the FDC, the internal sector count will
be complete when the FDC reads the last byte
from its side of the FIFO. There may be a delay
in the removal of the transfer request signal of
up to the time taken for the FDC to read the last
16 bytes from the FIFO. The host must tolerate
this delay.

Result Phase

The generation of FINT determines the
beginning of the result phase. For each of the
commands, a defined set of result bytes has to
be read from the FDC before the result phase is
complete. These bytes of data must be read out
for another command to start.

RQM and DIO must both equal "1" before the
result bytes may be read. After all the result
bytes have been read, the RQM and DIO bits
switch to "1" and "0" respectively, and the CB bit
is cleared, indicating that the FDC is ready to
accept the next command.

COMMAND SET/DESCRIPTIONS

Commands can be written whenever the FDC is
in the command phase. Each command has a
unique set of needed parameters and status
results. The FDC checks to see that the first
byte is a valid command and, if valid, proceeds
with the command. If it is invalid, an interrupt

is issued. The user sends a Sense Interrupt
Status command which returns an invalid
command error. Refer to Table 21 for
explanations of the various symbols used. Table
22 lists the required parameters and the results
associated with each command that the FDC is
capable of performing.

Table 21 - Description of Command Symbols

SYMBOL

NAME

DESCRIPTION

Cylinder Address

The currently selected address; 0 to 255.

Data Pattern

The pattern to be written in each sector data field during
formatting.

D0, D1, D2,
D3

Drive Select 0-3

Designates which drives are perpendicular drives on the
Perpendicular Mode Command. A "1" indicates a perpendicular
drive.

DIR

Direction Control

If this bit is 0, then the head will step out from the spindle during a
relative seek. If set to a 1, the head will step in toward the spindle.

DS0, DS1

Disk Drive Select

DS1 DS0 DRIVE

0 0 drive 0

0 1 drive 1

1 0 drive 2

1 1 drive 3

DTL

Special Sector
Size

By setting N to zero (00), DTL may be used to control the number
of bytes transferred in disk read/write commands. The sector size
(N = 0) is set to 128. If the actual sector (on the diskette) is larger
than DTL, the remainder of the actual sector is read but is not
passed to the host during read commands; during write
commands, the remainder of the actual sector is written with all
zero bytes. The CRC check code is calculated with the actual
sector. When N is not zero, DTL has no meaning and should be
set to FF HEX.

Enable Count

When this bit is "1" the "DTL" parameter of the Verify command
becomes SC (number of sectors per track).

EFIFO

Enable FIFO

This active low bit when a 0, enables the FIFO. A "1" disables the
FIFO (default).

EIS

Enable Implied
Seek

When set, a seek operation will be performed before executing any
read or write command that requires the C parameter in the
command phase. A "0" disables the implied seek.

EOT

End of Track

The final sector number of the current track.

Table 21 - Description of Command Symbols

SYMBOL

NAME

DESCRIPTION

GAP

Alters Gap 2 length when using Perpendicular Mode.

GPL

Gap Length

The Gap 3 size. (Gap 3 is the space between sectors excluding
the VCO synchronization field).

H/HDS

Head Address

Selected head: 0 or 1 (disk side 0 or 1) as encoded in the sector
ID field.

HLT

Head Load Time

The time interval that FDC waits after loading the head and before
initializing a read or write operation. Refer to the Specify
command for actual delays.

HUT

Head Unload
Time

The time interval from the end of the execution phase (of a read or
write command) until the head is unloaded. Refer to the Specify
command for actual delays.

LOCK

Lock defines whether EFIFO, FIFOTHR, and PRETRK
parameters of the CONFIGURE COMMAND can be reset to their
default values by a "software Reset". (A reset caused by writing to
the appropriate bits of either tha DSR or DOR)

MFM

MFM/FM Mode
Selector

A one selects the double density (MFM) mode. A zero selects
single density (FM) mode.

Table 21 - Description of Command Symbols

SYMBOL

NAME

DESCRIPTION

Multi-Track
Selector

When set, this flag selects the multi-track operating mode. In this
mode, the FDC treats a complete cylinder under head 0 and 1 as
a single track. The FDC operates as this expanded track started
at the first sector under head 0 and ended at the last sector under
head 1. With this flag set, a multitrack read or write operation will
automatically continue to the first sector under head 1 when the
FDC finishes operating on the last sector under head 0.

Sector Size Code

This specifies the number of bytes in a sector. If this parameter is
"00", then the sector size is 128 bytes. The number of bytes
transferred is determined by the DTL parameter. Otherwise the
sector size is (2 raised to the "N'th" power) times 128. All values
up to "07" hex are allowable. "07"h would equal a sector size of
16k. It is the user's responsibility to not select combinations that
are not possible with the drive.

NCN

New Cylinder
Number

The desired cylinder number.

Non-DMA Mode
Flag

When set to 1, indicates that the FDC is to operate in the non-
DMA mode. In this mode, the host is interrupted for each data
transfer. When set to 0, the FDC operates in DMA mode,
interfacing to a DMA controller by means of the DRQ and nDACK
signals.

Overwrite

The bits D0-D3 of the Perpendicular Mode Command can only be
modified if OW is set to 1. OW id defined in the Lock command.

PCN

Present Cylinder
Number

The current position of the head at the completion of Sense
Interrupt Status command.

POLL

Polling Disable

When set, the internal polling routine is disabled. When clear,
polling is enabled.

PRETRK

Precompensation
Start Track
Number

Programmable from track 00 to FFH.

Sector Address

The sector number to be read or written. In multi-sector transfers,
this parameter specifies the sector number of the first sector to be
read or written.

RCN

Relative Cylinder
Number

Relative cylinder offset from present cylinder as used by the
Relative Seek command.

Number of
Sectors Per Track

The number of sectors per track to be initialized by the Format
command. The number of sectors per track to be verified during a
Verify command when EC is set.

Table 21 - Description of Command Symbols

SYMBOL

NAME

DESCRIPTION

Skip Flag

When set to 1, sectors containing a deleted data address mark will
automatically be skipped during the execution of Read Data. If
Read Deleted is executed, only sectors with a deleted address
mark will be accessed. When set to "0", the sector is read or
written the same as the read and write commands.

SRT

Step Rate Interval The time interval between step pulses issued by the FDC.

Programmable from 0.5 to 8 milliseconds in increments of 0.5 ms
at the 1 Mbit data rate. Refer to the SPECIFY command for actual
delays.

ST0
ST1
ST2
ST3

Status 0
Status 1
Status 2
Status 3

Registers within the FDC which store status information after a
command has been executed. This status information is available
to the host during the result phase after command execution.

WGATE

Write Gate

Alters timing of WE to allow for pre-erase loads in perpendicular
drives.

INSTRUCTION SET

Table 22 - Instruction Set

READ DATA

PHASE

R/W

DATA BUS

REMARKS

Command

MFM

Command Codes

HDS DS1 DS0

--------

Sector ID information prior to
Command execution.

--------

-------

EOT

-------

GPL

-------

DTL

-------

Execution

Data transfer between the
FDD and system.

Result

-------

ST0

-------

Status information after
Command execution.

-------

ST1

-------

ST2

-------

--------

Sector ID information after
Command execution.

--------

READ DELETED DATA

PHASE

R/W

DATA BUS

REMARKS

Command

MFM

Command Codes

HDS DS1 DS0

--------

Sector ID information prior to
Command execution.

--------

-------

EOT

-------

GPL

-------

DTL

-------

Execution

Data transfer between the
FDD and system.

Result

-------

ST0

-------

Status information after
Command execution.

-------

ST1

-------

ST2

-------

--------

Sector ID information after
Command execution.

--------

WRITE DATA

PHASE

R/W

DATA BUS

REMARKS

Command

MFM

Command Codes

HDS DS1 DS0

--------

Sector ID information prior to
Command execution.

--------

-------

EOT

-------

GPL

-------

DTL

-------

Execution

Data transfer between the
FDD and system.

Result

-------

ST0

-------

Status information after
Command execution.

-------

ST1

-------

ST2

-------

--------

Sector ID information after
Command execution.

--------

WRITE DELETED DATA

PHASE

R/W

DATA BUS

REMARKS

Command

MFM

Command Codes

HDS

DS1

DS0

--------

Sector ID information
prior to Command
execution.

--------

-------

EOT

-------

GPL

-------

DTL

-------

Execution

Data transfer between
the FDD and system.

Result

-------

ST0

-------

Status information after
Command execution.

-------

ST1

-------

ST2

-------

--------

Sector ID information
after Command
execution.

--------

READ A TRACK

PHASE

R/W

DATA BUS

REMARKS

Command

MFM

Command Codes

HDS

DS1

DS0

--------

Sector ID information
prior to Command
execution.

--------

-------

EOT

-------

GPL

-------

DTL

-------

Execution

Data transfer between
the FDD and system.
FDC reads all of
cylinders' contents from
index hole to EOT.

Result

-------

ST0

-------

Status information after
Command execution.

-------

ST1

-------

ST2

-------

--------

Sector ID information
after Command
execution.

--------

VERIFY

PHASE

R/W

DATA BUS

REMARKS

Command

MFM

Command Codes

HDS

DS1

DS0

--------

Sector ID information
prior to Command
execution.

--------

-------

EOT

-------

GPL

-------

------

DTL/SC

------

Execution

No data transfer takes
place.

Result

-------

ST0

-------

Status information after
Command execution.

-------

ST1

-------

ST2

-------

--------

Sector ID information
after Command
execution.

--------

VERSION

PHASE

R/W

DATA BUS

REMARKS

Command

Command Code

Result

Enhanced Controller

FORMAT A TRACK

PHASE

R/W

DATA BUS

REMARKS

Command

MFM

Command Codes

HDS

DS1

DS0

--------

Bytes/Sector

--------

Sectors/Cylinder

-------

GPL

-------

Gap 3

--------

Filler Byte

Execution for
Each Sector
Repeat:

--------

Input Sector
Parameters

--------

FDC formats an entire
cylinder

Result

-------

ST0

-------

Status information after
Command execution

-------

ST1

-------

ST2

-------

------

Undefined

------

Undefined

------

Undefined

------

Undefined

------

SENSE DRIVE STATUS

PHASE

R/W

DATA BUS

REMARKS

Command

Command Codes

HDS

DS1

DS0

Result

-------

ST3

-------

Status information about
FDD

SEEK

PHASE

R/W

DATA BUS

REMARKS

Command

Command Codes

HDS

DS1

DS0

-------

NCN

-------

Execution

Head positioned over
proper cylinder on
diskette.

CONFIGURE

PHASE

R/W

DATA BUS

REMARKS

Command

Configure
Information

EIS EFIFO

POLL

---

FIFOTHR

---

Execution

---------

PRETRK

---------

RELATIVE SEEK

PHASE

R/W

DATA BUS

REMARKS

Command

DIR

HDS

DS1

DS0

-------

RCN

-------

DUMPREG

PHASE

R/W

DATA BUS

REMARKS

Command

*Note:
Registers
placed in
FIFO

Execution

Result

------

PCN-Drive 0

-------

------

PCN-Drive 1

-------

------

PCN-Drive 2

-------

------

PCN-Drive 3

-------

----

SRT

----

---

HUT

---

-------

HLT

-------

SC/EOT

-------

LOCK

GAP

WGATE

EIS EFIFO

POLL

FIFOTHR

--------

PRETRK

--------

PERPENDICULAR MODE

PHASE

R/W

DATA BUS

REMARKS

Command

Command Codes

GAP

WGATE

INVALID CODES

PHASE

R/W

DATA BUS

REMARKS

Command

-----

Invalid Codes

-----

Invalid Command Codes
(NoOp -
FDC37C665GT/666GT goes
into Standby State)

Result

-------

ST0

-------

ST0 = 80H

LOCK

PHASE

R/W

DATA BUS

REMARKS

Command

LOCK

Command Codes

Result

LOCK

SC is returned if the last command that was issued was the Format command. EOT is returned if the
last command was a Read or Write.

NOTE: These bits are used internally only. They are not reflected in the Drive Select pins. It is the
user's responsibility to maintain correspondence between these bits and the Drive Select pins (DOR).

DATA TRANSFER COMMANDS

All of the Read Data, Write Data and Verify type
commands use the same parameter bytes and
return the same results information, the only
difference being the coding of bits 0-4 in the first
byte.

An implied seek will be executed if the feature
was enabled by the Configure command. This
seek is completely transparent to the user. The
Drive Busy bit for the drive will go active in the
Main Status Register during the seek portion of
the command. If the seek portion fails, it will be
reflected in the results status normally returned
for a Read/Write Data command. Status
Register 0 (ST0) would contain the error code
and C would contain the cylinder on which the
seek failed.

Read Data

A set of nine (9) bytes is required to place the
FDC in the Read Data Mode. After the Read
Data command has been issued, the FDC loads
the head (if it is in the unloaded state), waits the
specified head settling time (defined in the
Specify command), and begins reading ID
Address Marks and ID fields. When the sector
address read off the diskette matches with the
sector address specified in the command, the
FDC reads the sector's data field and transfers
the data to the FIFO.

After completion of the read operation from the
current sector, the sector address is
incremented by one and the data from the next
logical sector is read and output via the FIFO.
This continuous read function is called "Multi-
Sector Read Operation". Upon receipt of TC, or
an implied TC (FIFO overrun/underrun), the
FDC stops sending data but will continue to
read data from the current sector, check the
CRC bytes, and at the end of the sector,
terminate the Read Data Command.

N determines the number of bytes per sector
(see Table 23 below). If N is set to zero, the
sector size is set to 128. The DTL value
determines the number of bytes to be
transferred. If DTL is less than 128, the FDC
transfers the specified number of bytes to the
host. For reads, it continues to read the entire
128-byte sector and checks for CRC errors. For
writes, it completes the 128-byte sector by filling
in zeros. If N is not set to 00 Hex, DTL should
be set to FF Hex and has no impact on the
number of bytes transferred.

Table 23 - Sector Sizes

The amount of data which can be handled with
a single command to the FDC depends upon
MT (multi-track) and N (number of bytes/sector).

The Multi-Track function (MT) allows the FDC to
read data from both sides of the diskette. For a
particular cylinder, data will be transferred
starting at Sector 1, Side 0 and completing the
last sector of the same track at Side 1.

If the host terminates a read or write operation
in the FDC, the ID information in the result
phase is dependent upon the state of the MT bit
and EOT byte. Refer to Table 24.

At the completion of the Read Data command,
the head is not unloaded until after the Head
Unload Time Interval (specified in the Specify
command) has elapsed. If the host issues
another command before the head unloads,
then the head settling time may be saved
between subsequent reads.

SECTOR SIZE

00
01
02
03

128 bytes
256 bytes
512 bytes

1024 bytes

...

16 Kbytes

If the FDC detects a pulse on the nINDEX pin
twice without finding the specified sector
(meaning that the diskette's index hole passes
through index detect logic in the drive twice), the
FDC sets the IC code in Status Register 0 to
"01" indicating abnormal termination, sets the
ND bit in Status Register 1 to "1" indicating a
sector not found, and terminates the Read Data
Command.

After reading the ID and Data Fields in each
sector, the FDC checks the CRC bytes. If a

CRC error occurs in the ID or data field, the
FDC sets the IC code in Status Register 0 to
"01" indicating abnormal termination, sets the
DE bit flag in Status Register 1 to "1", sets the
DD bit in Status Register 2 to "1" if CRC is
incorrect in the ID field, and terminates the Read
Data Command. Table 25 describes the effect
of the SK bit on the Read Data command
execution and results. Except where noted in
Table 25, the C or R value of the sector address
is automatically incremented (see Table 27).

Table 24 - Effects of MT and N Bits

MAXIMUM TRANSFER

CAPACITY

FINAL SECTOR READ

FROM DISK

0
1
0
1
0
1

1
1
2
2
3
3

256 x 26 = 6,656
256 x 52 = 13,312
512 x 15 = 7,680
512 x 30 = 15,360
1024 x 8 = 8,192
1024 x 16 = 16,384

26 at side 0 or 1
26 at side 1
15 at side 0 or 1
15 at side 1
8 at side 0 or 1
16 at side 1

Table 25 - Skip Bit vs Read Data Command

SK BIT
VALUE

DATA ADDRESS

MARK TYPE

ENCOUNTERED

RESULTS

SECTOR

READ?

CM BIT OF

ST2 SET?

DESCRIPTION

OF RESULTS

Normal Data

Deleted Data

Normal Data

Deleted Data

Yes

Normal
termination.
Address not
incremented.
Next sector not
searched for.
Normal
termination.
Normal
termination.
Sector not read
("skipped").

Read Deleted Data

This command is the same as the Read Data
command, only it operates on sectors that
contain a Deleted Data Address Mark at the
beginning of a Data Field.

Table 26 describes the effect of the SK bit on
the Read Deleted Data command execution and
results.

Except where noted in Table 26, the C or R
value of the sector address is automatically
incremented (see Table 27).

Table 26 - Skip Bit vs. Read Deleted Data Command

SK BIT
VALUE

DATA ADDRESS

MARK TYPE

ENCOUNTERED

RESULTS

SECTOR

READ?

CM BIT OF

ST2 SET?

DESCRIPTION

OF RESULTS

Normal Data

Deleted Data

Normal Data

Deleted Data

Yes

Address not
incremented.
Next sector not
searched for.
Normal
termination.
Normal
termination.
Sector not read
("skipped").
Normal
termination.

Read A Track

This command is similar to the Read Data
command except that the entire data field is
read continuously from each of the sectors of a
track. Immediately after encountering a pulse
on the nINDEX pin, the FDC starts to read all
data fields on the track as continuous blocks of
data without regard to logical sector numbers. If
the FDC finds an error in the ID or DATA CRC
check bytes, it continues to read data from the
track and sets the appropriate error bits at the
end of the command. The FDC compares the
ID information read from each sector with the
specified value in the command and sets the

ND flag of Status Register 1 to a "1" if there is
no comparison. Multi-track or skip operations
are not allowed with this command. The MT
and SK bits (bits D7 and D5 of the first
command byte respectively) should always be
set to "0".

This command terminates when the EOT
specified number of sectors has not been read.
If the FDC does not find an ID Address Mark on
the diskette after the second occurrence of a
pulse on the IDX pin, then it sets the IC code in
Status Register 0 to "01" (abnormal
termination), sets the MA bit in Status Register
1 to "1", and terminates the command.

Table 27 - Result Phase Table

HEAD

FINAL SECTOR

TRANSFERRED TO

HOST

D INFORMATION AT RESULT PHASE

Less than EOT

R + 1

Equal to EOT

C + 1

Less than EOT

R + 1

Equal to EOT

C + 1

Less than EOT

R + 1

Equal to EOT

LSB

Less than EOT

R + 1

Equal to EOT

C + 1

LSB

NC: No Change, the same value as the one at the beginning of command execution.
LSB: Least Significant Bit, the LSB of H is complemented.

Write Data

After the Write Data command has been issued,
the FDC loads the head (if it is in the unloaded
state), waits the specified head load time if
unloaded (defined in the Specify command),
and begins reading ID fields. When the sector
address read from the diskette matches the
sector address specified in the command, the
FDC reads the data from the host via the FIFO
and writes it to the sector's data field.

After writing data into the current sector, the
FDC computes the CRC value and writes it into
the CRC field at the end of the sector transfer.
The Sector Number stored in "R" is incremented
by one, and the FDC continues writing to the
next data field. The FDC continues this "Multi-
Sector Write Operation". Upon receipt of a
terminal count signal or if a FIFO over/under run
occurs while a data field is being written, then

the remainder of the data field is filled with
zeros.

The FDC reads the ID field of each sector and
checks the CRC bytes. If it detects a CRC error
in one of the ID fields, it sets the IC code in
Status Register 0 to "01" (abnormal
termination), sets the DE bit of Status Register 1
to "1", and terminates the Write Data command.

The Write Data command operates in much the
same manner as the Read Data command. The
following items are the same. Please refer to
the Read Data Command for details:

Transfer Capacity

EN (End of Cylinder) bit

ND (No Data) bit

Head Load, Unload Time Interval

ID information when the host terminates the
command

Definition of DTL when N = 0 and when N
does not = 0

Write Deleted Data

This command is almost the same as the Write
Data command except that a Deleted Data
Address Mark is written at the beginning of the
Data Field instead of the normal Data Address
Mark. This command is typically used to mark
a bad sector containing an error on the floppy
disk.

Verify

The Verify command is used to verify the data
stored on a disk. This command acts exactly
like a Read Data command except that no data
is transferred to the host. Data is read from the
disk and CRC is computed and checked against
the previously-stored value.

Because data is not transferred to the host, TC
(pin 35) cannot be used to terminate this
command. By setting the EC bit to "1", an
implicit TC will be issued to the FDC. This
implicit TC will occur when the SC value has
decremented to 0 (an SC value of 0 will verify
256 sectors). This command can also be
terminated by setting the EC bit to "0" and the
EOT value equal to the final sector to be
checked. If EC is set to "0", DTL/SC should be
programmed to 0FFH. Refer to Table 27 and
Table 28 for information concerning the values
of MT and EC versus SC and EOT value.

Definitions:

# Sectors Per Side = Number of formatted
sectors per each side of the disk.

# Sectors Remaining = Number of formatted
sectors left which can be read, including side 1
of the disk if MT is set to "1".

Table 28 - Verify Command Result Phase Table

SC/EOT VALUE

TERMINATION RESULT

SC = DTL
EOT

# Sectors Per Side

Success Termination
Result Phase Valid

SC = DTL
EOT > # Sectors Per Side

Unsuccessful Termination
Result Phase Invalid

# Sectors Remaining AND

EOT

# Sectors Per Side

Successful Termination
Result Phase Valid

SC > # Sectors Remaining OR
EOT > # Sectors Per Side

Unsuccessful Termination
Result Phase Invalid

SC = DTL
EOT

# Sectors Per Side

Successful Termination
Result Phase Valid

SC = DTL
EOT > # Sectors Per Side

Unsuccessful Termination
Result Phase Invalid

# Sectors Remaining AND

EOT

# Sectors Per Side

Successful Termination
Result Phase Valid

SC > # Sectors Remaining OR
EOT > # Sectors Per Side

Unsuccessful Termination
Result Phase Invalid

Format A Track

The Format command allows an entire track to
be formatted. After a pulse from the IDX pin is
detected, the FDC starts writing data on the disk
including gaps, address marks, ID fields, and
data fields per the IBM System 34 or 3740
format (MFM or FM respectively). The particular
values that will be written to the gap and data
field are controlled by the values programmed
into N, SC, GPL, and D which are specified by
the host during the command phase. The data
field of the sector is filled with the data byte
specified by D. The ID field for each sector is
supplied by the host; that is, four data bytes per
sector are needed by the FDC for C, H, R, and
N (cylinder, head, sector number and sector size
respectively).

After formatting each sector, the host must send
new values for C, H, R and N to the FDC for the
next sector on the track. The R value (sector
number) is the only value that must be changed
by the host after each sector is formatted. This
allows the disk to be formatted with
nonsequential sector addresses (interleaving).
This incrementing and formatting continues for
the whole track until the FDC encounters a pulse
on the IDX pin again and it terminates the
command.

Table 29 contains typical values for gap fields
which are dependent upon the size of the sector
and the number of sectors on each track. Actual
values can vary due to drive electronics.

FORMAT FIELDS

SYSTEM 34 (DOUBLE DENSITY) FORMAT

GAP4a

80x

SYNC

12x

IAM

GAP1

50x

SYNC

12x

IDAM

C
Y

H
D

S
E
C

N
O

C
R
C

GAP2

22x

SYNC

12x

DATA

C
R
C

GAP3

GAP 4b

SYSTEM 3740 (SINGLE DENSITY) FORMAT

GAP4a

40x

SYNC

IAM

GAP1

26x

SYNC

IDAM

C
Y

H
D

S
E
C

N
O

C
R
C

GAP2

11x

SYNC

DATA

C
R
C

GAP3

GAP 4b

FB or

PERPENDICULAR FORMAT

GAP4a

80x

SYNC

12x

IAM

GAP1

50x

SYNC

12x

IDAM

C
Y

H
D

S
E
C

N
O

C
R
C

GAP2

41x

SYNC

12x

DATA

C
R
C

GAP3

GAP 4b

Table 29 - Typical Values for Formatting

FORMAT

SECTOR SIZE

GPL1

GPL2

5.25"

Drives

128
128
512

1024
2048
4096

...

00
00
02
03
04
05

...

12
10
08
04
02
01

07
10
18
46

C8
C8

09
19
30
87

FF
FF

MFM

256
256

512*

1024
2048
4096

...

01
01
02
03
04
05

...

12
10
09
04
02
01

C8
C8

32
50
F0

FF
FF

3.5"

Drives

128
256
512

0
1
2

0F
09
05

07
0F

1B
2A
3A

MFM

256

512**

1024

1
2
3

0F
09
05

0E
1B

36
54
74

GPL1 = suggested GPL values in Read and Write commands to avoid splice point
between data field and ID field of contiguous sections.
GPL2 = suggested GPL value in Format A Track command.
*PC/AT values (typical)
**PS/2 values (typical). Applies with 1.0 MB and 2.0 MB drives.
NOTE: All values except sector size are in hex.

CONTROL COMMANDS

Control commands differ from the other
commands in that no data transfer takes place.
Three commands generate an interrupt when
complete: Read ID, Recalibrate, and Seek. The
other control commands do not generate an
interrupt.

Read ID

The Read ID command is used to find the
present position of the recording heads. The
FDC stores the values from the first ID field it is
able to read into its registers. If the FDC does
not find an ID address mark on the diskette after
the second occurrence of a pulse on the
nINDEX pin, it then sets the IC code in Status
Register 0 to "01" (abnormal termination), sets
the MA bit in Status Register 1 to "1", and
terminates the command.

The following commands will generate an
interrupt upon completion. They do not return
any result bytes. It is highly recommended that
control commands be followed by the Sense
Interrupt Status command. Otherwise, valuable
interrupt status information will be lost.

Recalibrate

This command causes the read/write head
within the FDC to retract to the track 0 position.
The FDC clears the contents of the PCN counter
and checks the status of the nTR0 pin from the
FDD. As long as the nTR0 pin is low, the DIR
pin remains 0 and step pulses are issued.
When the nTR0 pin goes high, the SE bit in
Status Register 0 is set to "1" and the command
is terminated. If the nTR0 pin is still low after 79
step pulses have been issued, the FDC sets the
SE and the EC bits of Status Register 0 to "1"
and terminates the command. Disks capable of
handling more than 80 tracks per side may
require more than one Recalibrate command to
return the head back to physical Track 0.

The Recalibrate command does not have a
result phase. The Sense Interrupt Status
command must be issued after the Recalibrate
command to effectively terminate it and to
provide verification of the head position (PCN).
During the command phase of the recalibrate
operation, the FDC is in the BUSY state, but
during the execution phase it is in a NON-BUSY
state. At this time, another Recalibrate
command may be issued, and in this manner
parallel Recalibrate operations may be done on
up to four drives at once.

Upon power up, the software must issue a
Recalibrate command to properly initialize all
drives and the controller.

Seek

The read/write head within the drive is moved
from track to track under the control of the Seek
command. The FDC compares the PCN, which
is the current head position, with the NCN and
performs the following operation if there is a
difference:

PCN < NCN: Direction signal to drive set to
"1" (step in) and issues step pulses.
PCN > NCN: Direction signal to drive set to
"0" (step out) and issues step pulses.

The rate at which step pulses are issued is
controlled by SRT (Stepping Rate Time) in the
Specify command. After each step pulse is
issued, NCN is compared against PCN, and
when NCN = PCN the SE bit in Status Register
0 is set to "1" and the command is terminated.

During the command phase of the seek or
recalibrate operation, the FDC is in the BUSY
state, but during the execution phase it is in the
NON-BUSY state. At this time, another Seek or
Recalibrate command may be issued, and in
this manner, parallel seek operations may be
done on up to four drives at once.

Note that if implied seek is not enabled, the read
and write commands should be preceded by:
1) Seek command - Step to the proper track
2) Sense Interrupt Status command -

Terminate the Seek command

3) Read ID - Verify head is on proper track
4) Issue Read/Write command.

The Seek command does not have a result
phase. Therefore, it is highly recommended that
the Sense Interrupt Status command be issued
after the Seek command to terminate it and to
provide verification of the head position (PCN).
The H bit (Head Address) in ST0 will always
return to a "0". When exiting POWERDOWN
mode, the FDC clears the PCN value and the
status information to zero. Prior to issuing the
POWERDOWN command, it is highly
recommended that the user service all pending
interrupts through the Sense Interrupt Status
command.

Sense Interrupt Status

An interrupt signal on FINT pin is generated by
the FDC for one of the following reasons:

1. Upon entering the Result Phase of:

a. Read Data command
b. Read A Track command
c. Read ID command
d. Read Deleted Data command
e. Write Data command
f.

Format A Track command

g. Write Deleted Data command
h. Verify command

2. End of Seek, Relative Seek, or Recalibrate

command

3. FDC requires a data transfer during the

execution phase in the non-DMA mode

The Sense Interrupt Status command resets the
interrupt signal and, via the IC code and SE bit
of Status Register 0, identifies the cause of the
interrupt.

Table 30 - Interrupt Identification

The Seek, Relative Seek, and Recalibrate
commands have no result phase. The Sense
Interrupt Status command must be issued
immediately after these commands to terminate
them and to provide verification of the head
position (PCN). The H (Head Address) bit in
ST0 will always return a "0". If a Sense Interrupt
Status is not issued, the drive will continue to be
BUSY and may affect the operation of the next
command.

Sense Drive Status

Sense Drive Status obtains drive status
information. It has not execution phase and
goes directly to the result phase from the
command phase. Status Register 3 contains
the drive status information.

Specify

The Specify command sets the initial values for
each of the three internal times. The HUT
(Head Unload Time) defines the time from the
end of the execution phase of one of the
read/write commands to the head unload state.
The SRT (Step Rate Time) defines the time
interval between adjacent step pulses. Note that
the spacing between the first and second step
pulses may be shorter than the remaining step
pulses. The HLT (Head Load Time) defines

INTERRUPT DUE TO

0
1

11
00

Polling
Normal termination of Seek
or Recalibrate command
Abnormal termination of
Seek or Recalibrate
command

the time between when the Head Load signal
goes high and the read/write operation starts.

The values change with the data rate speed
selection and are documented in Table 31. The
values are the same for MFM and FM.

Table 31 - Drive Control Delays (ms)

HUT

SRT

500K

300K

250K

500K

300K

250K

0
1
..

E
F

128

8
..

112
120

256

224
240

426

26.7

373
400

512

448
480

8.0
7.5

1.0
0.5

16
15

..
2
1

26.7

3.33
1.67

32
30

..
4
2

HLT

500K

300K

250K

00
01
02

7F
7F

128

1
2
..

126
127

256

2
4
..

252
254

426

3.3
6.7

420
423

512

4
8

504
508

The choice of DMA or non-DMA operations is
made by the ND bit. When this bit is "1", the
non-DMA mode is selected, and when ND is "0",
the DMA mode is selected. In DMA mode, data
transfers are signalled by the FDRQ pin. Non-
DMA mode uses the RQM bit and the FINT pin
to signal data transfers.

Configure

The Configure command is issued to select the
special features of the FDC. A Configure
command need not be issued if the default
values of the FDC meet the system
requirements.

Configure Default Values:

EIS - No Implied Seeks
EFIFO - FIFO Disabled
POLL - Polling Enabled
FIFOTHR - FIFO Threshold Set to 1 Byte

PRETRK - Pre-Compensation Set to Track 0
EIS - Enable Implied Seek. When set to "1", the
FDC will perform a Seek operation before
executing a read or write command. Defaults to
no implied seek.

EFIFO - A "1" disables the FIFO (default). This
means data transfers are asked for on a byte-
by-byte basis. Defaults to "1", FIFO disabled.
The threshold defaults to "1".

POLL - Disable polling of the drives. Defaults to
"0", polling enabled. When enabled, a single
interrupt is generated after a reset. No polling is
performed while the drive head is loaded and
the head unload delay has not expired.

FIFOTHR - The FIFO threshold in the execution
phase of read or write commands. This is
programmable from 1 to 16 bytes. Defaults to
one byte. A "00" selects one byte; "0F" selects
16 bytes.

PRETRK - Pre-Compensation Start Track
Number. Programmable from track 0 to 255.
Defaults to track 0. A "00" selects track 0; "FF"
selects track 255.

Version

The Version command checks to see if the
controller is an enhanced type or the older type
(765A). A value of 90 H is returned as the result
byte.

Relative Seek

The command is coded the same as for Seek,
except for the MSB of the first byte and the DIR
bit.

DIR

Head Step Direction Control

RCN Relative Cylinder Number that

determines how many tracks to step the
head in or out from the current track
number.

The Relative Seek command differs from the
Seek command in that it steps the head the
absolute number of tracks specified in the
command instead of making a comparison
against an internal register. The Seek
command is good for drives that support a
maximum of 256 tracks. Relative Seeks cannot
be overlapped with other Relative Seeks. Only
one Relative Seek can be active at a time.
Relative Seeks may be overlapped with Seeks
and Recalibrates. Bit 4 of Status Register 0
(EC) will be set if Relative Seek attempts to step
outward beyond Track 0.

As an example, assume that a floppy drive has
300 useable tracks. The host needs to read
track 300 and the head is on any track (0-255).
If a Seek command is issued, the head will stop

at track 255. If a Relative Seek command is
issued, the FDC will move the head the
specified number of tracks, regardless of the
internal cylinder position register (but will
increment the register). If the head was on track
40 (d), the maximum track that the FDC could
position the head on using Relative Seek will be
295 (D), the initial track + 255 (D). The
maximum count that the head can be moved
with a single Relative Seek command is 255
(D).

The internal register, PCN, will overflow as the
cylinder number crosses track 255 and will
contain 39 (D). The resulting PCN value is thus
(RCN + PCN) mod 256. Functionally, the FDC
starts counting from 0 again as the track
number goes above 255 (D). It is the user's
responsibility to compensate FDC functions
(precompensation track number) when
accessing tracks greater than 255. The FDC
does not keep track that it is working in an
"extended track area" (greater than 255). Any
command issued will use the current PCN value
except for the Recalibrate command, which only
looks for the TRACK0 signal. Recalibrate will
return an error if the head is farther than 79 due
to its limitation of issuing a maximum of 80 step
pulses. The user simply needs to issue a
second Recalibrate command. The Seek
command and implied seeks will function
correctly within the 44 (D) track (299-255) area
of the "extended track area". It is the user's
responsibility not to issue a new track position
that will exceed the maximum track that is
present in the extended area.

To return to the standard floppy range (0-255) of
tracks, a Relative Seek should be issued to
cross the track 255 boundary.

A Relative Seek can be used instead of the
normal Seek, but the host is required to
calculate the difference between the current
head location and the new (target) head
location. This may require the host to issue a
Read ID command to ensure that the head is
physically on the track that software assumes it

DIR

ACTION

0
1

Step Head Out
Step Head In

to be. Different FDC commands will return
different cylinder results which may be difficult
to keep track of with software without the Read
ID command.

Perpendicular Mode

The Perpendicular Mode command should be
issued prior to executing Read/Write/Format
commands that access a disk drive with
perpendicular recording capability. With this
command, the length of the Gap2 field and VCO
enable timing can be altered to accommodate
the unique requirements of these drives. Table
31 describes the effects of the WGATE and
GAP bits for the Perpendicular Mode command.
Upon a reset, the FDC will default to the
conventional mode (WGATE = 0, GAP = 0).

Selection of the 500 Kbps and 1 Mbps
perpendicular modes is independent of the
actual data rate selected in the Data Rate Select
Register. The user must ensure that these two
data rates remain consistent.

The Gap2 and VCO timing requirements for
perpendicular recording type drives are dictated
by the design of the read/write head. In the
design of this head, a pre-erase head precedes
the normal read/write head by a distance of 200
micrometers. This works out to about 38 bytes
at a 1 Mbps recording density. Whenever the
write head is enabled by the Write Gate signal,
the pre-erase head is also activated at the same
time. Thus, when the write head is initially
turned on, flux transitions recorded on the media
for the first 38 bytes will not be preconditioned
with the pre-erase head since it has not yet been
activated. To accommodate this head activation
and deactivation time, the Gap2 field is
expanded to a length of 41 bytes. The format
field shown on page 67 illustrates

the change in the Gap2 field size for the
perpendicular format.

On the read back by the FDC, the controller
must begin synchronization at the beginning of
the sync field. For the conventional mode, the
internal PLL VCO is enabled (VCOEN)
approximately 24 bytes from the start of the
Gap2 field. But, when the controller operates in
the 1 Mbps perpendicular mode (WGATE = 1,
GAP = 1), VCOEN goes active after 43 bytes to
accommodate the increased Gap2 field size. For
both cases, and approximate two-byte cushion
is maintained from the beginning of the sync
field for the purposes of avoiding write splices in
the presence of motor speed variation.

For the Write Data case, the FDC activates
Write Gate at the beginning of the sync field
under the conventional mode. The controller
then writes a new sync field, data address mark,
data field, and CRC as shown on page 67. With
the pre-erase head of the perpendicular drive,
the write head must be activated in the Gap2
field to insure a proper write of the new sync
field. For the 1 Mbps perpendicular mode
(WGATE = 1, GAP = 1), 38 bytes will be written
in the Gap2 space. Since the bit density is
proportional to the data rate, 19 bytes will be
written in the Gap2 field for the 500 Kbps
perpendicular mode (WGATE = 1, GAP =0).

It should be noted that none of the alterations in
Gap2 size, VCO timing, or Write Gate timing
affect normal program flow. The information
provided here is just for background purposes
and is not needed for normal operation. Once
the Perpendicular Mode command is invoked,
FDC software behavior from the user standpoint
is unchanged.

The perpendicular mode command is enhanced
to allow specific drives to be designated
Perpendicular recording drives. This
enhancement allows data transfers between
Conventional and Perpendicular drives without
having to issue Perpendicular mode commnds
between the accesses of the different drive

types, nor having to change write pre-
compensation values.

When both GAP and WGATE bits of the
PERPENDICULAR MODE COMMAND are both
programmed to "0" (Conventional mode), then
D0, D1, D2, D3, and D4 can be programmed
independently to "1" for that drive to be set
automatically to Perpendicular mode. In this
mode the following set of conditions also apply:
1. The GAP2 written to a perpendicular drive

during a write operation will depend upon the
programmed data rate.

2. The write pre-compensation given to a

perpendicular mode drive will be 0ns.

3. For D0-D3 programmed to "0" for

conventional mode drives any data written
will be at the currently programmed write
pre-compensation.

Note: Bits D0-D3 can only be overwritten when

OW is programmed as a "1".
If either GAP or WGATE is a "1" then
D0-D3 are ignored.

Software and hardware resets have the
following effect on the PERPENDICULAR
MODE COMMAND:
1. "Software" resets (via the DOR or DSR

registers) will only clear GAP and WGATE
bits to "0". D0-D3 are unaffected and retain
their previous value.

2. "Hardware" resets will clear all bits ( GAP,

WGATE and D0-D3) to "0", i.e all
conventional mode.

Table 32 - Effects of WGATE and GAP Bits

WGATE

GAP

MODE

LENGTH OF

GAP2

FORMAT

FIELD

PORTION OF

GAP 2

WRITTEN BY
WRITE DATA

OPERATION

0
0

0
1

Conventional
Perpendicular
(500 Kbps)
Reserved
(Conventional)
Perpendicular
(1 Mbps)

22 Bytes
22 Bytes

22 Bytes

41 Bytes

0 Bytes

19 Bytes

0 Bytes

38 Bytes

LOCK

In order to protect systems with long DMA
latencies against older application software that
can disable the FIFO the LOCK Command has
been added. This command should only be
used by the FDC routines, and application
software should refrain from using it. If an
application calls for the FIFO to be disabled
then the CONFIGURE command should be
used.

The LOCK command defines whether the
EFIFO, FIFOTHR, and PRETRK parameters of
the CONFIGURE command can be RESET by
the DOR and DSR registers. When the LOCK
bit is set to logic "1" all subsequent "software
RESETS by the DOR and DSR registers will not
change the previously set parameters to their
default values. All "hardware" RESET from the
RESET pin will set the LOCK bit to logic "0" and
return the EFIFO, FIFOTHR, and PRETRK to
their default values. A status byte is returned
immediately after issuing a a LOCK command.

This byte reflects the value of the LOCK bit set
by the command byte.

ENHANCED DUMPREG

The DUMPREG command is designed to
support system run-time diagnostics and
application software development and debug.
To accommodate the LOCK command and the
enhanced PERPENDICULAR MODE command
the eighth byte of the DUMPREG command has
been modified to contain the additional data
from these two commands.

COMPATIBILITY

The FDC37C665GT/666GT was designed with
software compatibility in mind. It is a fully
backwards- compatible solution with the older
generation 765A/B disk controllers. The FDC
also implements on-board registers for
compatibility with the PS/2, as well as PC/AT
and PC/XT, floppy disk controller subsystems.
After a hardware reset of the FDC, all registers,
functions and enhancements default to a PC/AT,
PS/2 or PS/2 Model 30 compatible operating
mode, depending on how the IDENT and MFM
bits are configured by the system bios.

PARALLEL PORT FLOPPY DISK CONTROLLER

In this mode, the Floppy Disk Control signals
are available on the parallel port pins. When
this mode is selected, the parallel port is not
available. There are two modes of operation,
PPFD1 and PPFD2. These modes can be
selected in Configuration Register 4. PPFD1
has only drive 1 on the parallel port pins; PPFD2
has drive 0 and 1 on the parallel port pins.

PPFD1:

Drive 0 is on the FDC pins

Drive 1 is on the Parallel port pins
Drive 2 is on the FDC pins*
Drive 3 is on the FDC pins*

PPFD2:

Drive 0 is on the Parallel port
pins

Drive 1 is on the Parallel port pins
Drive 2 is on the FDC pins*
Drive 3 is on the FDC pins*

* If ECP is selected, then direct support for
drives 2 and 3 is not available. Drives 2 and 3
are available using external decoders.

When the PPFDC is selected the following pins
are set as follows:

nDS2/PDIR (pin 98): not ECP = high-Z,
ECP = high

A10/nDS3 (pin 97): high-Z, A10 = to
internal logic.

nMTR2/nPDACK (pin 96): high-Z

nMTR3/PDRQ (pin 99): not ECP = high-Z,
ECP & dmaEn = 0, ECP & not dmaEn =
high-Z

PINTR: not active, this is hi-Z or Low
depending on settings.

The following parallel port pins are read as
follows by a read of the parallel port register:

Data Register (read) = last Data Register
(write)

Control Register are read as "cable not
connected" STROBE, AUTOFD and SLC =
0 and nINIT = 1;

Status Register reads: nBUSY = 0, PE = 0,
SLCT = 0, nACK = 1, nERR = 1.

The following FDC pins are all in the high
impedence state when the PPFDC is actually
selected by the drive select register:

nWDATA, DENSEL, nHDSEL, nWGATE,
nDIR, nSTEP, nDS1, nDS0, nMTRO,
nMTR1.

If PPFDx is selected, then the parallel port
can not be used as a parallel port until
"Normal" mode is selected.

The FDC signals are muxed onto the Parallel
Port pins as shown in Table 33:

SERIAL PORT (UART)

The FDC37C665GT and FDC37C666GT
incorporate two full function UARTs. They are
compatible with the NS16450, the 16450 ACE
registers and the NS16550A. The UARTS
perform serial-to-parallel conversion on received
characters and parallel-to-serial conversion on
transmit characters. The data rates are
independently programmable from 115.2K baud
down to 50 baud. The character options are
programmable for 1 start; 1, 1.5 or 2 stop bits;
even, odd, sticky or no parity; and prioritized
interrupts. The UARTS each contain a
programmable baud rate generator that is
capable of dividing the input clock or crystal by
a number from 1 to 65535. The UARTs are also
capable of supporting the MIDI data rate. Refer
to the FDC37C665GT Configuration Registers
and the FDC37C666GT Hardware

Configuration description for information on
disabling, power down and changing the base
address of the UARTS. The interrupt from a
UART is enabled by programming OUT2 of that
UART to a logic "1". OUT2 being a logic "0"
disables that UART's interrupt.

REGISTER DESCRIPTION

Addressing of the accessible registers of the
Serial Port is shown below. The base
addresses of the serial ports are defined by the
configuration registers (see Configuration
section). The Serial Port registers are located at
sequentially increasing addresses above these
base addresses. The FDC37C665GT/666GT
contains two serial ports, each of which contain
a register set as described below.

Table 34 - Addressing the Serial Port

DLAB*

REGISTER NAME

Receive Buffer (read)

Transmit Buffer (write)

Interrupt Enable (read/write)

Interrupt Identification (read)

FIFO Control (write)

Line Control (read/write)

Modem Control (read/write)

Line Status (read/write)

Modem Status (read/write)

Scratchpad (read/write)

Divisor LSB (read/write)

Divisor MSB (read/write

*NOTE: DLAB is Bit 7 of the Line Control Register

The following section describes the operation of
the registers.

RECEIVE BUFFER REGISTER (RB)
Address Offset = 0H, DLAB = 0, READ ONLY

This register holds the received incoming data
byte. Bit 0 is the least significant bit, which is
transmitted and received first. Received data is
double buffered; this uses an additional shift
register to receive the serial data stream and
convert it to a parallel 8 bit word which is
transferred to the Receive Buffer register. The
shift register is not accessible.

TRANSMIT BUFFER REGISTER (TB)
Address Offset = 0H, DLAB = 0, WRITE ONLY

This register contains the data byte to be
transmitted. The transmit buffer is double
buffered, utilizing an additional shift register (not
accessible) to convert the 8 bit data word to a
serial format. This shift register is loaded from
the Transmit Buffer when the transmission of
the previous byte is complete.

INTERRUPT ENABLE REGISTER (IER)
Address Offset = 1H, DLAB = 0, READ/WRITE

The lower four bits of this register control the
enables of the five interrupt sources of the Serial
Port interrupt. It is possible to totally disable the
interrupt system by resetting bits 0 through 3 of
this register. Similarly, setting the appropriate
bits of this register to a high, selected interrupts
can be enabled. Disabling the interrupt system
inhibits the Interrupt Identification Register and
disables any Serial Port interrupt out of the
FDC37C665. All other system functions operate
in their normal manner, including the Line
Status and MODEM Status Registers. The
contents of the Interrupt Enable Register are
described below.

Bit 0
This bit enables the Received Data Available
Interrupt (and timeout interrupts in the FIFO
mode) when set to logic "1".

Bit 1
This bit enables the Transmitter Holding
Register Empty Interrupt when set to logic "1".

Bit 2
This bit enables the Received Line Status
Interrupt when set to logic "1". The error
sources causing the interrupt are Overrun,
Parity, Framing and Break. The Line Status
Register must be read to determine the source.

Bit 3
This bit enables the MODEM Status Interrupt
when set to logic "1". This is caused when one
of the Modem Status Register bits changes
state.

Bits 4 through 7
These bits are always logic "0".

FIFO CONTROL REGISTER (FCR)
Address Offset = 2H, DLAB = X, WRITE

This is a write only register at the same location
as the IIR. This register is used to enable and
clear the FIFO's, set the RCVR FIFO trigger
level. Note: DMA is not supported.

Bit 0
Setting this bit to a logic "1" enables both the
XMIT and RCVR FIFO's. Clearing this bit to a
logic "0" disables both the XMIT and RCVR
FIFO's and clears all bytes from both FIFO's.
When changing from FIFO Mode to non-FIFO
(16450) mode, data is automatically cleared
from the FIFO's. This bit must be a 1 when
other bits in this register are written to or they
will not be properly programmed.

Bit 1
Setting this bit to a logic "1" clears all bytes in
the RCVR FIFO and resets its counter logic to 0.
The shift register is not cleared. This bit is self-
clearing.

Bit 2
Setting this bit to a logic "1" clears all bytes in
the XMIT FIFO and resets its counter logic to 0.
The shift register is not cleared. This bit is self-
clearing.

Bit 3
Writting to this bit has no effect on the operation
of the UART. The RXRDY and TXRDY pins are
not available on this chip.

Bit 4,5
Reserved

Bit 6,7

These bits are used to set the trigger level for
the RCVR FIFO interrupt.
INTERRUPT IDENTIFICATION REGISTER
(IIR)
Address Offset = 2H, DLAB = X, READ

By accessing this register, the host CPU can
determine the highest priority interrupt and its
source. Four levels of priority interrupt exist.
They are in descending order of priority:

1. Receiver Line Status (highest priority)
2. Received Data Ready

3. Transmitter Holding Register Empty
4. MODEM Status (lowest priority)

Information indicating that a prioritized interrupt
is pending and the source of that interrupt is
stored in the Interrupt Identification Register
(refer to Interrupt Control Table). When the
CPU accesses the IIR, the Serial Port freezes all
interrupts and indicates the highest priority
pending interrupt to the CPU. During this CPU
access, even if the Serial Port records new
interrupts, the current indication does not
change until access is completed. The contents
of the IIR are described below.

Bit 0
This bit can be used in either a hardwired
prioritized or polled environment to indicate
whether an interrupt is pending. When bit 0 is a
logic "0", an interrupt is pending and the
contents of the IIR may be used as a pointer to
the appropriate internal service routine. When
bit 0 is a logic "1", no interrupt is pending.

Bits 1 and 2
These two bits of the IIR are used to identify the
highest priority interrupt pending as indicated by
the Interrupt Control Table.

Bit 3

In non-FIFO mode, this bit is a logic "0". In
FIFO mode this bit is set along with bit 2 when a
timeout interrupt is pending.

Bits 4 and 5
These bits of the IIR are always logic "0".

Bits 6 and 7
These two bits are set when the FIFO
CONTROL Register bit 0 equals 1.

Bit 7

Bit 6

RCVR FIFO

Trigger Level

(BYTES)

Table 35 - Interrupt Control Table

FIFO

MODE

ONLY

INTERRUPT

IDENTIFICATION

REGISTER

INTERRUPT SET AND RESET FUNCTIONS

BIT

PRIORIT

Y LEVEL

INTERRUPT

TYPE

INTERRUPT

SOURCE

INTERRUPT

RESET

CONTROL

None

Highest

Receiver Line
Status

Overrun Error,
Parity Error,
Framing Error or
Break Interrupt

Reading the Line
Status Register

Second

Received Data
Available

Receiver Data
Available

Read Receiver
Buffer or the
FIFO drops
below the trigger
level.

Second

Character
Timeout
Indication

No Characters
Have Been
Removed From
or Input to the
RCVR FIFO
during the last 4
Char times and
there is at least 1
char in it during
this time

Reading the
Receiver Buffer
Register

Third

Transmitter
Holding Register
Empty

Reading the IIR
Register (if
Source of
Interrupt) or
Writing the
Transmitter
Holding Register

Fourth

MODEM Status

Clear to Send or
Data Set Ready
or Ring Indicator
or Data Carrier
Detect

Reading the
MODEM Status
Register

LINE CONTROL REGISTER (LCR)
Address Offset = 3H, DLAB = 0, READ/WRITE

This register contains the format information of
the serial line. The bit definitions are:

Bits 0 and 1
These two bits specify the number of bits in
each transmitted or received serial character.
The encoding of bits 0 and 1 is as follows:

The Start, Stop and Parity bits are not included
in the word length.

Bit 2
This bit specifies the number of stop bits in each
transmitted or received serial character. The
following table summarizes the information.

Note: The receiver will ignore all stop bits
beyond the first, regardless of the number used
in transmitting.

Bit 3
Parity Enable bit. When bit 3 is a logic "1", a
parity bit is generated (transmit data) or
checked (receive data) between the last data
word bit and the first stop bit of the serial data.
(The parity bit is used to generate an even or

odd number of 1s when the data word bits and
the parity bit are summed).

Bit 4
Even Parity Select bit. When bit 3 is a logic "1"
and bit 4 is a logic "0", an odd number of logic
"1"'s is transmitted or checked in the data word
bits and the parity bit. When bit 3 is a logic "1"
and bit 4 is a logic "1" an even number of bits is
transmitted and checked.

Bit 5
Stick Parity bit. When bit 3 is a logic "1" and bit
5 is a logic "1", the parity bit is transmitted and
then detected by the receiver in the opposite
state indicated by bit 4.

Bit 6
Set Break Control bit. When bit 6 is a logic "1",
the transmit data output (TXD) is forced to the
Spacing or logic "0" state and remains there
(until reset by a low level bit 6) regardless of
other transmitter activity. This feature enables
the Serial Port to alert a terminal in a
communications system.

Bit 7
Divisor Latch Access bit (DLAB). It must be set
high (logic "1") to access the Divisor Latches of
the Baud Rate Generator during read or write
operations. It must be set low (logic "0") to
access the Receiver Buffer Register, the
Transmitter Holding Register, or the Interrupt
Enable Register.

MODEM CONTROL REGISTER (MCR)
Address Offset = 4H, DLAB = X,
READ/WRITE

This 8 bit register controls the interface with the
MODEM or data set (or device emulating a
MODEM). The contents of the MODEM control
register are described below.

BIT 1

BIT 0 WORD LENGTH

0
0
1
1

0
1
0
1

5 Bits
6 Bits
7 Bits
8 Bits

BIT 2

WORD LENGTH

NUMBER OF

STOP BITS

5 bits

1.5

6 bits

7 bits

8 bits

Bit 0
This bit controls the Data Terminal Ready
(nDTR) output. When bit 0 is set to a logic "1",
the nDTR output is forced to a logic "0". When
bit 0 is a logic "0", the nDTR output is forced to
a logic "1".

Bit 1
This bit controls the Request To Send (nRTS)
output. Bit 1 affects the nRTS output in a
manner identical to that described above for bit
0.

Bit 2
This bit controls the Output 1 (OUT1) bit. This
bit does not have an output pin and can only be
read or written by the CPU.

Bit 3
Output 2 (OUT2). This bit is used to enable an
UART interrupt. When OUT2 is a logic "0", the
serial port interrupt output is forced to a high
impedance state - disabled. When OUT2 is a
logic "1", the serial port interrupt outputs are
enabled.

Bit 4
This bit provides the loopback feature for
diagnostic testing of the Serial Port. When bit 4
is set to logic "1", the following occur:

1. The TXD is set to the Marking State(logic

"1").

2. The receiver Serial Input (RXD) is

disconnected.

3. The output of the Transmitter Shift Register

is "looped back" into the Receiver Shift
Register input.

4. All MODEM Control inputs (nCTS, nDSR,

nRI and nDCD) are disconnected.

5. The four MODEM Control outputs (nDTR,

nRTS, and OUT2) are internally connected
to the four MODEM Control inputs.

6. The Modem Control output pins are forced

inactive high.

7. Data that is transmitted is immediately

received.

This feature allows the processor to verify the
transmit and receive data paths of the Serial
Port. In the diagnostic mode, the receiver and
the transmitter interrupts are fully operational.
The MODEM Control Interrupts are also
operational but the interrupts' sources are now
the lower four bits of the MODEM Control
Register instead of the MODEM Control inputs.
The interrupts are still controlled by the Interrupt
Enable Register.

Bits 5 through 7
These bits are permanently set to logic zero.

LINE STATUS REGISTER (LSR)
Address Offset = 5H, DLAB = X,
READ/WRITE

Bit 0
Data Ready (DR). It is set to a logic "1"
whenever a complete incoming character has
been received and transferred into the Receiver
Buffer Register or the FIFO. Bit 0 is reset to a
logic "0" by reading all of the data in the Receive
Buffer Register or the FIFO.

Bit 1
Overrun Error (OE). Bit 1 indicates that data in
the Receiver Buffer Register was not read before
the next character was transferred into the
register, thereby destroying the previous
character. In FIFO mode, an overrun error will
occur only when the FIFO is full and the next
character has been completely received in the
shift register, the character in the shift register is
overwritten but not transferred to the FIFO. The
OE indicator is set to a logic "1" immediately
upon detection of an overrun condition, and
reset whenever the Line Status Register is read.

Bit 2
Parity Error (PE). Bit 2 indicates that the
received data character does not have the
correct even or odd parity, as selected by the
even parity select bit. The PE is set to a logic
"1" upon detection of a parity error and is reset
to a logic "0" whenever the Line Status Register
is read. In the FIFO mode this error is

associated with the particular character in the
FIFO it applies to. This error is indicated when
the associated character is at the top of the
FIFO.

Bit 3
Framing Error (FE). Bit 3 indicates that the
received character did not have a valid stop bit.
Bit 3 is set to a logic "1" whenever the stop bit
following the last data bit or parity bit is detected
as a zero bit (Spacing level). The FE is reset to
a logic "0" whenever the Line Status Register is
read. In the FIFO mode this error is associated
with the particular character in the FIFO it
applies to. This error is indicated when the
associated character is at the top of the FIFO.
The Serial Port will try to resynchronize after a
framing error. To do this, it assumes that the
framing error was due to the next start bit, so it
samples this 'start' bit twice and then takes in
the 'data'.

Bit 4
Break Interrupt (BI). Bit 4 is set to a logic "1"
whenever the received data input is held in the
Spacing state (logic "0") for longer than a full
word transmission time (that is, the total time of
the start bit + data bits + parity bits + stop bits).
The BI is reset after the CPU reads the contents
of the Line Status Register. In the FIFO mode
this error is associated with the particular
character in the FIFO it applies to. This error is
indicated when the associated character is at
the top of the FIFO. When break occurs only
one zero character is loaded into the FIFO.
Restarting after a break is received, requires the
serial data (RXD) to be logic "1" for at least 1/2
bit time.

Note: Bits 1 through 4 are the error conditions
that produce a Receiver Line Status Interrupt
whenever any of the corresponding conditions
are detected and the interrupt is enabled.

Bit 5
Transmitter Holding Register Empty (THRE). Bit
5 indicates that the Serial Port is ready to accept
a new character for transmission. In addition,
this bit causes the Serial Port to issue an
interrupt when the Transmitter Holding Register
interrupt enable is set high. The THRE bit is set
to a logic "1" when a character is transferred
from the Transmitter Holding Register into the
Transmitter Shift Register. The bit is reset to
logic "0" whenever the CPU loads the
Transmitter Holding Register. In the FIFO mode
this bit is set when the XMIT FIFO is empty, it is
cleared when at least 1 byte is written to the
XMIT FIFO. Bit 5 is a read only bit.

Bit 6
Transmitter Empty (TEMT). Bit 6 is set to a
logic "1" whenever the Transmitter Holding
Register (THR) and Transmitter Shift Register
(TSR) are both empty. It is reset to logic "0"
whenever either the THR or TSR contains a data
character. Bit 6 is a read only bit. In the FIFO
mode this bit is set whenever the THR and TSR
are both empty,

Bit 7
This bit is permanently set to logic "0" in the 450
mode. In the FIFO mode, this bit is set to a
logic "1" when there is at least one parity error,
framing error or break indication in the FIFO.
This bit is cleared when the LSR is read if there
are no subsequent errors in the FIFO.

MODEM STATUS REGISTER (MSR)
Address Offset = 6H, DLAB = X,
READ/WRITE

This 8 bit register provides the current state of
the control lines from the MODEM (or peripheral
device). In addition to this current state
information, four bits of the MODEM Status
Register (MSR) provide change information.
These bits are set to logic "1" whenever a
control input from the MODEM changes state.
They are reset to logic "0" whenever the
MODEM Status Register is read.

Bit 0
Delta Clear To Send (DCTS). Bit 0 indicates
that the nCTS input to the chip has changed
state since the last time the MSR was read.

Bit 1
Delta Data Set Ready (DDSR). Bit 1 indicates
that the nDSR input has changed state since the
last time the MSR was read.

Bit 2
Trailing Edge of Ring Indicator (TERI). Bit 2
indicates that the nRI input has changed from
logic "0" to logic "1".

Bit 3
Delta Data Carrier Detect (DDCD). Bit 3
indicates that the nDCD input to the chip has
changed state.

NOTE: Whenever bit 0, 1, 2, or 3 is set to a
logic "1", a MODEM Status Interrupt is
generated.

Bit 4
This bit is the complement of the Clear To Send
(nCTS) input. If bit 4 of the MCR is set to logic
"1", this bit is equivalent to nRTS in the MCR.

Bit 5
This bit is the complement of the Data Set
Ready (nDSR) input. If bit 4 of the MCR is set
to logic "1", this bit is equivalent to DTR in the
MCR.

Bit 6
This bit is the complement of the Ring Indicator
(nRI) input. If bit 4 of the MCR is set to logic
"1", this bit is equivalent to OUT1 in the MCR.

Bit 7
This bit is the complement of the Data Carrier

Detect (nDCD) input. If bit 4 of the MCR is set
to logic "1", this bit is equivalent to OUT2 in the
MCR.

SCRATCHPAD REGISTER (SCR)
Address Offset =7H, DLAB =X, READ/WRITE

This 8 bit read/write register has no effect on the
operation of the Serial Port. It is intended as a
scratchpad register to be used by the
programmer to hold data temporarily.

PROGRAMMABLE BAUD RATE GENERATOR
(AND DIVISOR LATCHES DLH, DLL)

The Serial Port contains a programmable Baud
Rate Generator that is capable of taking any
clock input (DC to 3 MHz) and dividing it by any
divisor from 1 to 65535. This output frequency
of the Baud Rate Generator is 16x the Baud
rate. Two 8 bit latches store the divisor in 16 bit
binary format. These Divisor Latches must be
loaded during initialization in order to insure
desired operation of the Baud Rate Generator.
Upon loading either of the Divisor Latches, a 16
bit Baud counter is immediately loaded. This
prevents long counts on initial load. If a 0 is
loaded into the BRG registers the output divides
the clock by the number 3. If a 1 is loaded the
output is the inverse of the input oscillator. If a
two is loaded the output is a divide by 2 signal
with a 50% duty cycle. If a 3 or greater is
loaded the output is low for 2 bits and high for
the remainder of the count. The input clock to
the BRG is the 24 MHz crystal divided by 13,
giving a 1.8462 MHz clock.

Table 36 shows the baud rates possible with a
1.8462 MHz crystal.

Effect Of The Reset on Register File

The Reset Function Table (Table 37) details the
effect of the Reset input on each of the registers
of the Serial Port.

FIFO INTERRUPT MODE OPERATION

When the RCVR FIFO and receiver interrupts
are enabled (FCR bit 0 = "1", IER bit 0 = "1"),
RCVR interrupts occur as follows:

A. The receive data available interrupt will be

issued when the FIFO has reached its
programmed trigger level; it is cleared as
soon as the FIFO drops below its
programmed trigger level.

B. The IIR receive data available indication

also occurs when the FIFO trigger level is
reached. It is cleared when the FIFO drops
below the trigger level.

C. The receiver line status interrupt (IIR=06H),

has higher priority than the received data
available (IIR=04H) interrupt.

D. The data ready bit (LSR bit 0)is set as soon

as a character is transferred from the shift
register to the RCVR FIFO. It is reset when
the FIFO is empty.

When RCVR FIFO and receiver interrupts are
enabled, RCVR FIFO timeout interrupts occur
as follows:

A. A FIFO timeout interrupt occurs if all the

following conditions exist:

at least one character is in the FIFO

The most recent serial character received
was longer than 4 continuous character
times ago. (If 2 stop bits are programmed,
the second one is included in this time
delay.)

The most recent CPU read of the FIFO was
longer than 4 continuous character times
ago.

This will cause a maximum character received
to interrupt issued delay of 160 msec at 300
BAUD with a 12 bit character.

B. Character times are calculated by using the

RCLK input for a clock signal (this makes
the delay proportional to the baudrate).

C. When a timeout interrupt has occurred it is

cleared and the timer reset when the CPU
reads one character from the RCVR FIFO.

D. When a timeout interrupt has not occurred

the timeout timer is reset after a new
character is received or after the CPU reads
the RCVR FIFO.

When the XMIT FIFO and transmitter interrupts
are enabled (FCR bit 0 = "1", IER bit 1 = "1"),
XMIT interrupts occur as follows:

A. The transmitter holding register interrupt

(02H) occurs when the XMIT FIFO is
empty; it is cleared as soon as the
transmitter holding register is written to (1
of 16 characters may be written to the XMIT
FIFO while servicing this interrupt) or the
IIR is read.

B. The transmitter FIFO empty indications will

be delayed 1 character time minus the last
stop bit time whenever the following occurs:
THRE=1 and there have not been at least
two bytes at the same time in the transmitte
FIFO since the last THRE=1. The
transmitter interrupt after changing FCR0
will be immediate, if it is enabled.

Character timeout and RCVR FIFO trigger level
interrupts have the sme priority as the current
received data available interrupt; XMIT FIFO
empty has the same priority as the current
transmitter holding register empty interrupt.

FIFO POLLED MODE OPERATION

With FCR bit 0 = "1" resetting IER bits 0, 1, 2 or
3 or all to zero puts the UART in the FIFO
Polled Mode of operation. Since the RCVR and
XMITTER are controlled separately, either one
or both can be in the polled mode of operation.

In this mode, the user's program will check
RCVR and XMITTER status via the LSR. LSR
definitions for the FIFO Polled Mode are as
follows:

Bit 0=1 as long as there is one byte in the

RCVR FIFO.

Bits 1 to 4 specify which error(s) have

occurred. Character error status is handled
the same way as when in the interrupt

mode, the IIR is not affected since EIR bit

2=0.

Bit 5 indicates when the XMIT FIFO is

empty.

Bit 6 indicates that both the XMIT FIFO and

shift register are empty.

Bit 7 indicates whether there are any errors

in the RCVR FIFO.

There is no trigger level reached or timeout
condition indicated in the FIFO Polled Mode,
however, the RCVR and XMIT FIFO's are still
fully capable of holding characters.

Table 36 - Baud Rates Using 1.8462 MHz Clock (24 MHz/13)

DESIRED BAUD

RATE

DIVISOR USED TO

GENERATE 16X CLOCK

PERCENT ERROR DIFFERENCE

BETWEEN DESIRED AND ACTUAL*

2304

0.001

1536

110

1047

134.5

857

0.004

150

768

300

384

600

192

1200

1800

2000

0.005

2400

3600

4800

7200

9600

19200

38400

0.030

57600

0.16

115200

0.16

*Note: The percentage error for all baud rates, except where indicated otherwise, is 0.2%.

Table 37 - Reset Function Table

REGISTER/SIGNAL

RESET CONTROL

RESET STATE

Interrupt Enable Register

RESET

All bits low

Interrupt Identification Reg.

RESET

Bit 0 is high; Bits 1 thru 7 low

FIFO Control

RESET

All bits low

Line Control Reg.

RESET

All bits low

MODEM Control Reg.

RESET

All bits low

Line Status Reg.

RESET

All bits low except 5, 6 high

MODEM Status Reg.

RESET

Bits 0 - 3 low; Bits 4 - 7 input

TXD1, TXD2

RESET

High

INTRPT (RCVR errs)

RESET/Read LSR

Low

INTRPT (RCVR Data Ready)

RESET/Read RBR

Low

INTRPT (THRE)

RESET/ReadIIR/Write THR

Low

OUT2B

RESET

High

RTSB

RESET

High

DTRB

RESET

High

OUT1B

RESET

High

RCVR FIFO

RESET/FCR1*FCR0/_FCR0

All Bits Low

XMIT FIFO

RESET/FCR1*FCR0/_FCR0

All Bits Low

Table 38 - Register Summary for an Individual UART Channel

REGISTER

ADDRESS*

REGISTER NAME

REGISTER

SYMBOL

BIT 0

BIT 1

ADDR = 0

DLAB = 0

Receive Buffer Register (Read Only)

RBR

Data Bit 0
(Note 1)

Data Bit 1

ADDR = 0

DLAB = 0

Transmitter Holding Register (Write
Only)

THR

Data Bit 0

Data Bit 1

ADDR = 1

DLAB = 0

Interrupt Enable Register

IER

Enable
Received
Data
Available
Interrupt
(ERDAI)

Enable
Transmitter
Holding
Register
Empty
Interrupt
(ETHREI)

ADDR = 2

Interrupt Ident. Register (Read Only)

IIR

"0" if Interrupt
Pending

Interrupt ID
Bit

ADDR = 2

FIFO Control Register (Write Only)

FCR

FIFO Enable

RCVR FIFO
Reset

ADDR = 3

Line Control Register

LCR

Word Length
Select Bit 0
(WLS0)

Word Length
Select Bit 1
(WLS1)

ADDR = 4

MODEM Control Register

MCR

Data
Terminal
Ready (DTR)

Request to
Send (RTS)

ADDR = 5

Line Status Register

LSR

Data Ready
(DR)

Overrun
Error (OE)

ADDR = 6

MODEM Status Register

MSR

Delta Clear to
Send (DCTS)

Delta Data
Set Ready
(DDSR)

ADDR = 7

Scratch Register (Note 4)

SCR

Bit 0

Bit 1

ADDR = 0

DLAB = 1

Divisor Latch (LS)

DDL

Bit 0

Bit 1

ADDR = 1

DLAB = 1

Divisor Latch (MS)

DLM

Bit 8

Bit 9

*DLAB is Bit 7 of the Line Control Register (ADDR = 3).

Note 1: Bit 0 is the least significant bit. It is the first bit serially transmitted or received.

Note 2: When operating in the XT mode, this bit will be set any time that the transmitter shift register is empty.

Table 38 - Register Summary for an Individual UART Channel (continued)

BIT 2

BIT 3

BIT 4

BIT 5

BIT 6

BIT 7

Data Bit 2

Data Bit 3

Data Bit 4

Data Bit 5

Data Bit 6

Data Bit 7

Data Bit 2

Data Bit 3

Data Bit 4

Data Bit 5

Data Bit 6

Data Bit 7

Enable
Receiver Line
Status
Interrupt
(ELSI)

Enable
MODEM
Status
Interrupt
(EMSI)

Interrupt ID
Bit

Interrupt ID
Bit (Note 5)

FIFOs
Enabled
(Note 5)

XMIT FIFO
Reset

DMA Mode
Select (Note
6)

Reserved

RCVR Trigger
LSB

RCVR Trigger
MSB

Number of
Stop Bits
(STB)

Parity Enable
(PEN)

Even Parity
Select (EPS)

Stick Parity

Set Break

Divisor Latch
Access Bit
(DLAB)

OUT1

(Note 3)

OUT2

(Note 3)

Loop

Parity Error
(PE)

Framing Error
(FE)

Break
Interrupt (BI)

Transmitter
Holding
Register
(THRE)

Transmitter
Empty
(TEMT) (Note
2)

Error in
RCVR FIFO
(Note 5)

Trailing Edge
Ring Indicator
(TERI)

Delta Data
Carrier Detect
(DDCD)

Clear to Send
(CTS)

Data Set
Ready (DSR)

Ring Indicator
(RI)

Data Carrier
Detect (DCD)

Bit 2

Bit 3

Bit 4

Bit 5

Bit 6

Bit 7

Bit 2

Bit 3

Bit 4

Bit 5

Bit 6

Bit 7

Bit 10

Bit 11

Bit 12

Bit 13

Bit 14

Bit 15

Note 3: This bit no longer has a pin associated with it.

Note 4: When operating in the XT mode, this register is not available.

Note 5: These bits are always zero in the non-FIFO mode.

Note 6: Writing a one to this bit has no effect. DMA modes are not supported in this chip.

NOTES ON SERIAL PORT OPERATION

FIFO MODE OPERATION:

GENERAL

The RCVR FIFO will hold up to 16 bytes
regardless of which trigger level is selected.

TX AND RX FIFO OPERATION

The Tx portion of the UART transmits data
through TXD as soon as the CPU loads a byte
into the Tx FIFO. The UART will prevent
loads to the Tx FIFO if it currently holds 16
characters. Loading to the Tx FIFO will again
be enabled as soon as the next character is
transferred to the Tx shift register. These
capabilities account for the largely autonomous
operation of the Tx.

The UART starts the above operations typically
with a Tx interrupt. The chip issues a Tx
interrupt whenever the Tx FIFO is empty and the
Tx interrupt is enabled, except in the following
instance. Assume that the Tx FIFO is empty
and the CPU starts to load it. When the first
byte enters the FIFO the Tx FIFO empty
interrupt will transition from active to inactive.
Depending on the execution speed of the service
routine software, the UART may be able to
transfer this byte from the FIFO to the shift
register before the CPU loads another byte. If
this happens, the Tx FIFO will be empty again
and typically the UART's interrupt line would
transition to the active state. This could cause a
system with an interrupt control unit to record a
Tx FIFO empty condition, even though the CPU
is currently servicing that interrupt. Therefore,
after the first byte has been loaded into the
FIFO the UART will wait one serial character
transmission time before issuing a new Tx
FIFO empty interrupt.

This one character Tx interrupt delay will
remain active until at least two bytes have
been loaded into the FIFO, concurrently.
When the Tx FIFO empties after this
condition, the Tx interrupt will be activated
without a one character delay.

Rx support functions and operation are quite
different from those described for the
transmitter. The Rx FIFO receives data until the
number of bytes in the FIFO equals the selected
interrupt trigger level. At that time if Rx
interrupts are enabled, the UART will issue an
interrupt to the CPU. The Rx FIFO will continue
to store bytes until it holds 16 of them. It will not
accept any more data when it is full. Any more
data entering the Rx shift register will set the
Overrun Error flag. Normally, the FIFO depth
and the programmable trigger levels will give the
CPU ample time to empty the Rx FIFO before
an overrun occurs.

One side-effect of having a Rx FIFO is that the
selected interrupt trigger level may be above the
data level in the FIFO. This could occur when
data at the end of the block contains fewer bytes
than the trigger level. No interrupt would be
issued to the CPU and the data would remain in
the UART. To prevent the software from
having to check for this situation the chip
incorporates a timeout interrupt.

The timeout interrupt is activated when there is
a least one byte in the Rx FIFO, and neither the
CPU nor the Rx shift register has accessed the
Rx FIFO within 4 character times of the last
byte. The timeout interrupt is cleared or reset
when the CPU reads the Rx FIFO or another
character enters it.

These FIFO related features allow optimization
of CPU/UART transactions and are especially
useful given the higer baud rate capability (256
kbaud).

PARALLEL PORT

The FDC37C665GT and FDC37C666GT
incorporate one IBM XT/AT compatible parallel
port. The FDC37C665GT and FDC37C666GT
support the optional PS/2 type bi-directional
parallel port (SPP), the Enhanced Parallel Port
(EPP) and the Extended Capabilities Port (ECP)
parallel port modes. Refer to the
FDC37C665GT Configuration Registers and
FDC37C666GT Hardware Configuration
description for information on disabling, power
down, changing the base address of the parallel
port, and selecting the mode of operation.

The FDC37C665GT and FDC37C666GT also
incorporate SMSC's ChiProtect circuitry,
which prevents possible damage to the parallel
port due to printer power-up.

The functionality of the Parallel Port is achieved
through the use of eight addressable ports,
with their associated registers and control
gating. The control and data port are read/write
by the CPU, the status port is read/write in the
EPP mode. The address map of the Parallel
Port is shown below:

DATA PORT

BASE ADDRESS + 00H

STATUS PORT

BASE ADDRESS + 01H

CONTROL PORT

BASE ADDRESS + 02H

EPP ADDR PORT

BASE ADDRESS + 03H

EPP DATA PORT 0

BASE ADDRESS + 04H

EPP DATA PORT 1

BASE ADDRESS + 05H

EPP DATA PORT 2

BASE ADDRESS + 06H

EPP DATA PORT 3

BASE ADDRESS + 07H

The bit map of these registers is:

Note

DATA PORT

PD0

PD1

PD2

PD3

PD4

PD5

PD6

PD7

STATUS
PORT

TMOUT

nERR

SLCT

nACK

nBUSY

CONTROL
PORT

STROBE

AUTOFD

nINIT

SLC

IRQE

PCD

EPP ADDR
PORT

PD0

PD1

PD2

PD3

PD4

PD5

PD6

AD7

2,3

EPP DATA
PORT 0

PD0

PD1

PD2

PD3

PD4

PD5

PD6

PD7

2,3

EPP DATA
PORT 1

PD0

PD1

PD2

PD3

PD4

PD5

PD6

PD7

2,3

EPP DATA
PORT 2

PD0

PD1

PD2

PD3

PD4

PD5

PD6

PD7

2,3

EPP DATA
PORT 3

PD0

PD1

PD2

PD3

PD4

PD5

PD6

PD7

2,3

Note 1: These registers are available in all modes.

Note 2: These registers are only available in EPP mode.

Note 3 : For EPP mode, IOCHRDY must be connected to the ISA bus.

Table 39 - Parallel Port Connector

HOST

CONNECTOR

PIN NUMBER

STANDARD

EPP

ECP

nStrobe

nWrite

nStrobe

2-9

71-68, 66-63

PData<0:7>

nAck

Intr

nAck

Busy

nWait

Busy, PeriphAck(3)

(NU)

PError,

nAckReverse(3)

Select

(NU)

Select

nAutofd

nDatastb

nAutoFd,

HostAck(3)

nError

(NU)

nFault(1)

nPeriphRequest(3)

nInit

(NU)

nInit(1)

nReverseRqst(3)

nSelectin

nAddrstrb

nSelectIn(1,3)

(1) = Compatible Mode

(3) = High Speed Mode

Note: For the cable interconnection required for ECP support and the Slave Connector pin numbers,

refer to the IEEE 1284 Extended Capabilities Port Protocol and ISA Standard, Rev. 1.09, Jan.
7, 1993. This document is available from Microsoft.

IBM XT/AT COMPATIBLE, BI-DIRECTIONAL
AND EPP MODES

DATA PORT

ADDRESS OFFSET = 00H

The Data Port is located at an offset of '00H'
from the base address. The data register is
cleared at initialization by RESET. During a
WRITE operation, the Data Register latches the
contents of the data bus with the rising edge of
the nIOW input. The contents of this register
are buffered (non inverting) and output onto the
PD0 - PD7 ports. During a READ operation in
SPP mode, PD0 - PD7 ports are buffered (not
latched) and output to the host CPU.

STATUS PORT

ADDRESS OFFSET = 01H

The Status Port is located at an offset of '01H'
from the base address. The contents of this
register are latched for the duration of an nIOR
read cycle. The bits of the Status Port are
defined as follows:

BIT 0 TMOUT - TIME OUT

This bit is valid in EPP mode only and indicates
that a 10 usec time out has occured on the EPP
bus. A logic 0 means that no time out error has
occured; a logic 1 means that a time out error
has been detected. This bit is cleared by a
RESET. Writing a one to this bit clears the time
out status bit. On a write, this bit is self clearing
and does not require a write of a zero. Writing
a zero to this bit has no effect.

BITS 1, 2 - are not implemented as register bits,
during a read of the Printer Status Register
these bits are a low level.

BIT 3 nERR - nERROR

The level on the nERROR input is read by the
CPU as bit 3 of the Printer Status Register. A
logic O means an error has been detected; a
logic 1 means no error has been detected.

BIT 4 SLCT - PRINTER SELECTED STATUS

The level on the SLCT input is read by the CPU
as bit 4 of the Printer Status Register. A logic 1
means the printer is on line; a logic 0 means it is
not selected.

BIT 5 PE - PAPER END

The level on the PE input is read by the CPU as
bit 5 of the Printer Status Register. A logic 1
indicates a paper end; a logic 0 indicates the
presence of paper.

BIT 6 nACK - nACKNOWLEDGE

The level on the nACK input is read by the CPU
as bit 6 of the Printer Status Register. A logic 0
means that the printer has received a character
and can now accept another. A logic 1 means
that it is still processing the last character or has
not received the data.

BIT 7 nBUSY - nBUSY

The complement of the level on the BUSY input
is read by the CPU as bit 7 of the Printer Status
Register. A logic 0 in this bit means that the
printer is busy and cannot accept a new
character. A logic 1 means that it is ready to
accept the next character.

CONTROL PORT

ADDRESS OFFSET = 02H

The Control Port is located at an offset of '02H'
from the base address. The Control Register is
initialized by the RESET input, bits 0 to 5 only
being affected; bits 6 and 7 are hard wired low.

BIT 0 STROBE - STROBE

This bit is inverted and output onto the
nSTROBE output.

BIT 1 AUTOFD - AUTOFEED

This bit is inverted and output onto the
nAUTOFD output. A logic 1 causes the printer
to generate a line feed after each line is printed.
A logic 0 means no autofeed.

BIT 2 nINIT - nINITIATE OUTPUT

This bit is output onto the nINIT output without
inversion.

BIT 3 SLCTIN - PRINTER SELECT INPUT

This bit is inverted and output onto the nSLCTIN
output. A logic 1 selects the printer; a logic 0
means the printer is not selected.

BIT 4 IRQE - INTERRUPT REQUEST ENABLE

The interrupt request enable bit when set to a
high level may be used to enable interrupt
requests from the Parallel Port to the CPU. An
interrupt request is generated on the IRQ port by
a positive going nACK input. When the IRQE
bit is programmed low the IRQ is disabled.

BIT 5 PCD - PARALLEL CONTROL DIRECTION

Parallel Control Direction is valid in extended
mode only (CR#1<3>=0). In printer mode, the
direction is always out regardless of the state of
this bit. In bi-directional mode, a logic 0 means
that the printer port is in output mode (write); a
logic 1 means that the printer port is in input
mode (read).

Bits 6 and 7 during a read are a low level, and
cannot be written.

EPP ADDRESS PORT

ADDRESS OFFSET = 03H

The EPP Address Port is located at an offset of
'03H' from the base address. The address
register is cleared at initialization by RESET.
During a WRITE operation, the contents of DB0-
DB7 are buffered (non inverting) and output onto
the PD0 - PD7 ports, the leading edge of nIOW

causes an EPP ADDRESS WRITE cycle to be
performed, the trailing edge of IOW latches the
data for the duration of the EPP write cycle.
During a READ operation, PD0 - PD7 ports are
read, the leading edge of IOR causes an EPP
ADDRESS READ cycle to be performed and the
data output to the host CPU, the deassertion of
ADDRSTB latches the PData for the duration of
the IOR cycle. This register is only available in
EPP mode.

EPP DATA PORT 0

ADDRESS OFFSET = 04H

The EPP Data Port 0 is located at an offset of
'04H' from the base address. The data register
is cleared at initialization by RESET. During a
WRITE operation, the contents of DB0-DB7 are
buffered (non inverting) and output onto the PD0
- PD7 ports, the leading edge of nIOW causes
an EPP DATA WRITE cycle to be performed,
the trailing edge of IOW latches the data for the
duration of the EPP write cycle. During a READ
operation, PD0 - PD7 ports are read, the leading
edge of IOR causes an EPP READ cycle to be
performed and the data output to the host CPU,
the deassertion of DATASTB latches the PData
for the duration of the IOR cycle. This register
is only available in EPP mode.

EPP DATA PORT 1

ADDRESS OFFSET = 05H

The EPP Data Port 1 is located at an offset of
'05H' from the base address. Refer to EPP
DATA PORT 0 for a description of operation.
This register is only available in EPP mode.

EPP DATA PORT 2

ADDRESS OFFSET = 06H

The EPP Data Port 2 is located at an offset of
'06H' from the base address. Refer to EPP
DATA PORT 0 for a description of operation.
This register is only available in EPP mode.

EPP DATA PORT 3

ADDRESS OFFSET = 07H

The EPP Data Port 3 is located at an offset of
'07H' from the base address. Refer to EPP
DATA PORT 0 for a description of operation.
This register is only available in EPP mode.

EPP 1.9 OPERATION

When the EPP mode is selected in the
configuration register, the standard and bi-
directional modes are also available. If no EPP
Read, Write or Address cycle is currently
executing, then the PDx bus is in the standard or
bi-directional mode, and all output signals
(STROBE, AUTOFD, INIT) are as set by the
SPP Control Port and direction is controlled by
PCD of the Control port.

In EPP mode, the system timing is closely
coupled to the EPP timing. For this reason, a
watchdog timer is required to prevent system
lockup. The timer indicates if more than 10usec
have elapsed from the start of the EPP cycle
(nIOR or nIOW asserted) to nWAIT being
deasserted (after command). If a time-out
occurs, the current EPP cycle is aborted and the
time-out condition is indicated in Status bit 0.

During an EPP cycle, if STROBE is active, it
overrides the EPP write signal forcing the PDx
bus to always be in a write mode and the
nWRITE signal to always be asserted.

Software Constraints

Before an EPP cycle is executed, the software
must ensure that the control register bit PCD is
a logic "0" (ie a 04H or 05H should be written to
the Control port). If the user leaves PCD as a
logic "1", and attempts to perform an EPP write,
the chip is unable to perform the write (because
PCD is a logic "1") and will appear to perform an
EPP read on the parallel bus, no error is
indicated.

EPP 1.9 Write

The timing for a write operation (address or
data) is shown in timing diagram EPP Write
Data or Address cycle. IOCHRDY is driven
active low at the start of each EPP write and is
released when it has been determined that the
write cycle can complete. The write cycle can
complete under the following circumstances:

If the EPP bus is not ready (nWAIT is active
low) when nDATASTB or nADDRSTB goes
active then the write can complete when
nWAIT goes inactive high.

If the EPP bus is ready (nWAIT is inactive
high) then the chip must wait for it to go
active low before changing the state of
nDATASTB, nWRITE or nADDRSTB. The
write can complete once nWAIT is
determined inactive.

Write Sequence of operation

The host selects an EPP register, places
data on the SData bus and drives nIOW
active.

The chip drives IOCHRDY inactive (low).

If WAIT is not asserted, the chip must wait
until WAIT is asserted.

The chip places address or data on PData
bus, clears PDIR, and asserts nWRITE.

Chip asserts nDATASTB or nADDRSTRB
indicating that PData bus contains valid
information, and the WRITE signal is valid.

Peripheral deasserts nWAIT, indicating that
any setup requirements have been satisfied
and the chip may begin the termination
phase of the cycle.

The chip deasserts nDATASTB or
nADDRSTRB, this marks the beginning
of the termination phase. If it has not
already done so, the peripheral should
latch the information byte now.

The chip latches the data from the
SData bus for the PData bus and
asserts (releases) IOCHRDY allowing
the host to complete the write cycle.

Peripheral asserts nWAIT, indicating to the
host that any hold time requirements have
been satisfied and acknowledging the
termination of the cycle.

Chip may modify nWRITE and nPDATA in
preparation for the next cycle.

EPP 1.9 Read

The timing for a read operation (data) is shown
in timing diagram EPP Read Data cycle.
IOCHRDY is driven active low at the start of
each EPP read and is released when it has been
determined that the read cycle can complete.
The read cycle can complete under the following
circumstances:

1.If the EPP bus is not ready (nWAIT is active

low) when nDATASTB goes active then the
read can complete when nWAIT goes
inactive high.

2.If the EPP bus is ready (nWAIT is inactive

high) then the chip must wait for it to go
active low before changing the state of
WRITE or before nDATASTB goes active.
The read can complete once nWAIT is
determined inactive.

Read Sequence of Operation

The host selects an EPP register and drives
nIOR active.

The chip drives IOCHRDY inactive (low).

If WAIT is not asserted, the chip must wait
until WAIT is asserted.

The chip tri-states the PData bus and
deasserts nWRITE.

Chip asserts nDATASTB or nADDRSTRB
indicating that PData bus is tri-stated, PDIR
is set and the nWRITE signal is valid.

Peripheral drives PData bus valid.

Peripheral deasserts nWAIT, indicating that
PData is valid and the chip may begin the
termination phase of the cycle.

8. a)

The chip latches the data from the
PData bus for the SData bus,
deasserts nDATASTB or nADDRSTRB,
this marks the beginning of the
termination phase.

The chip drives the valid data onto the
SData bus and asserts (releases)
IOCHRDY allowing the host to
complete the read cycle.

Peripheral tri-states the PData bus and
asserts nWAIT, indicating to the host that
the PData bus is tri-stated.

10. Chip may modify nWRITE, PDIR and

nPDATA in preparation for the next cycle.

EPP 1.7 OPERATION

When the EPP 1.7 mode is selected in the
configuration register, the standard and bi-
directional modes are also available. If no EPP
Read, Write or Address cycle is currently
executing, then the PDx bus is in the standard or
bi-directional mode, and all output signals
(STROBE, AUTOFD, INIT) are as set by the
SPP Control Port and direction is controlled by
PCD of the Control port.

In EPP mode, the system timing is closely
coupled to the EPP timing. For this reason, a
watchdog timer is required to prevent system
lockup. The timer indicates if more than 10usec
have elapsed from the start of the EPP cycle
(nIOR or nIOW asserted) to the end of the cycle
nIOR or nIOW deasserted). If a time-out
occurs, the current EPP cycle is aborted and the
time-out condition is indicated in Status bit 0.

Software Constraints

Before an EPP cycle is executed, the software
must ensure that the control register bits D0, D1
and D3 are set to zero. Also, bit D5 (PCD) is a
logic "0" for an EPP write or a logic "1" for and
EPP read.

EPP 1.7 Write

The timing for a write operation (address or
data) is shown in timing diagram EPP 1.7 Write
Data or Address cycle. IOCHRDY is driven
active low when nWAIT is active low during the
EPP cycle. This can be used to extend the cycle
time. The write cycle can complete when
nWAIT is inactive high.

Write Sequence of Operation

The host sets PDIR bit in the control
register to a logic "0". This asserts
nWRITE.

The host selects an EPP register, places
data on the SData bus and drives nIOW
active.

The chip places address or data on PData
bus.

Chip asserts nDATASTB or nADDRSTRB
indicating that PData bus contains valid
information, and the WRITE signal is valid.

If nWAIT is asserted, IOCHRDY is
deasserted until the peripheral deasserts
nWAIT or a time-out occurs.

6. When the host deasserts nI0W the chip

deasserts nDATASTB or nADDRSTRB and
latches the data from the SData bus for the
PData bus.

Chip may modify nWRITE, PDIR and
nPDATA in preparation of the next cycle.

EPP 1.7 Read

The timing for a read operation (data) is shown
in timing diagram EPP 1.7 Read Data cycle.
IOCHRDY is driven active low when nWAIT is
active low during the EPP cycle. This can be
used to extend the cycle time. The read cycle
can complete when nWAIT is inactive high.

Read Sequence of Operation

The host sets PDIR bit in the control
register to a logic "1". This deasserts
nWRITE and tri-states the PData bus.

The host selects an EPP register and drives
nIOR active.

Chip asserts nDATASTB or nADDRSTRB
indicating that PData bus is tri-stated, PDIR
is set and the nWRITE signal is valid.

If nWAIT is asserted, IOCHRDY is
deasserted until the peripheral deasserts
nWAIT or a time-out occurs.

The Peripheral drives PData bus valid.

The Peripheral deasserts nWAIT, indicating
that PData is valid and the chip may begin
the termination phase of the cycle.

7. When the host deasserts nI0R the chip

deasserts nDATASTB or nADDRSTRB.

Peripheral tri-states the PData bus.

Chip may modify nWRITE, PDIR and
nPDATA in preparation of the next cycle.

Table 40 - EPP Pin Descriptions

EPP

SIGNAL

EPP NAME

TYPE

EPP DESCRIPTION

nWRITE

nWrite

This signal is active low. It denotes a write operation.

PD<0:7>

Address/Data

I/O

Bi-directional EPP byte wide address and data bus.

INTR

Interrupt

This signal is active high and positive edge triggered. (Pass
through with no inversion, Same as SPP.)

nWAIT

nWait

This signal is active low. It is driven inactive as a positive
acknowledgement from the device that the transfer of data
is completed. It is driven active as an indication that the
device is ready for the next transfer.

nDATASTB

nData Strobe

This signal is active low. It is used to denote data read or
write operation.

nRESET

nReset

This signal is active low. When driven active, the EPP
device is reset to its initial operational mode.

nADDRSTB

nAddress
Strobe

This signal is active low. It is used to denote address read
or write operation.

Paper End

Same as SPP mode.

SLCT

Printer
Selected
Status

Same as SPP mode.

nERR

nError

Same as SPP mode.

PDIR

Parallel Port
Direction

This output shows the direction of the data transfer on the
parallel port bus. A low means an output/write condition
and a high means an input/read condition. This signal is
normally a low (output/write) unless PCD of the control
register is set or if an EPP read cycle is in progress.

Note 1: SPP and EPP can use 1 common register.

Note 2: nWrite is the only EPP output that can be over-ridden by SPP control port during an EPP

cycle. For correct EPP read cycles, PCD is required to be a low.

100

EXTENDED CAPABILITIES PARALLEL PORT

ECP provides a number of advantages, some of
which are listed below. The individual features
are explained in greater detail in the remainder
of this section.

High performance half-duplex forward and
reverse channel

Interlocked handshake, for fast reliable
transfer

Optional single byte RLE compression for
improved throughput (64:1)

Channel addressing for low-cost peripherals

Maintains link and data layer separation

Permits the use of active output drivers

Permits the use of adaptive signal timing

Peer-to-peer capability

Vocabulary

The following terms are used in this document:

assert:

When a signal asserts it transitions to a
"true" state, when a signal deasserts it
transitions to a "false" state.

forward: Host to Peripheral communication.

reverse: Peripheral to Host communication.

PWord: A port word; equal in size to the width

of the ISA interface. For this
implementation, PWord is always 8
bits.

A high level.

A low level.

These terms may be considered synonymous:

PeriphClk, nAck

HostAck, nAutoFd

PeriphAck, Busy

nPeriphRequest, nFault

nReverseRequest, nInit

nAckReverse, PError

Xflag, Select

ECPMode, nSelectln

HostClk, nStrobe

Reference Document

The IEEE 1284 Extended Capabilities Port
Protocol and ISA Interface Standard, Rev 1.09,
Jan 7, 1993. This document is available from
Microsoft.

The bit map of the Extended Parallel Port
registers is:

Note

data

PD7

PD6

PD5

PD4

PD3

PD2

PD1

PD0

ecpAFifo

Addr/RLE

Address or RLE field

dsr

nBusy

nAck

PError

Select

nFault

dcr

Direction

ackIntEn

SelectIn

nInit

autofd

strobe

cFifo

Parallel Port Data FIFO

ecpDFifo

ECP Data FIFO

tFifo

Test FIFO

cnfgA

cnfgB

compress

intrValue

ecr

MODE

nErrIntrEn

dmaEn

serviceIntr

full

empty

Note 1: These registers are available in all modes.
Note 2: All FIFOs use one common 16 byte FIFO.

101

ISA IMPLEMENTATION STANDARD

This specification describes the standard ISA
interface to the Extended Capabilities Port
(ECP). All ISA devices supporting ECP must
meet the requirements contained in this section
or the port will not be supported by Microsoft.
For a description of the ECP Protocol, please
refer to the IEEE 1284 Extended Capabilities
Port Protocol and ISA Interface Standard, Rev.
1.09, Jan.7, 1993. This document is available
from Microsoft.

Description

The port is software and hardware compatible
with existing parallel ports so that it may be
used as a standard LPT port if ECP is not
required. The port is designed to be simple and
requires a small number of gates to implement.
It does not do any "protocol" negotiation, rather

it provides an automatic high burst-bandwidth
channel that supports DMA for ECP in both the
forward and reverse directions.

Small FIFOs are employed in both forward and
reverse directions to smooth data flow and
improve the maximum bandwidth requirement.
The size of the FIFO is 16 bytes deep. The port
supports an automatic handshake for the
standard parallel port to improve compatibility
mode transfer speed.

The port also supports run length encoded
(RLE) decompression (required) in hardware.
Compression is accomplished by counting
identical bytes and transmitting an RLE byte
that indicates how many times the next byte is
to be repeated. Decompression simply
intercepts the RLE byte and repeats the
following byte the specified number of times.
Hardware support for compression is optional.

102

Table 41 - ECP Pin Descriptions

NAME

TYPE

DESCRIPTION

nStrobe

During write operations nStrobe registers data or address into the slave
on the asserting edge (handshakes with Busy).

PData 7:0

I/O

Contains address or data or RLE data.

nAck

Indicates valid data driven by the peripheral when asserted. This signal
handshakes with nAutoFd in reverse.

PeriphAck (Busy)

This signal deasserts to indicate that the peripheral can accept data.
This signal handshakes with nStrobe in the forward direction. In the
reverse direction this signal indicates whether the data lines contain
ECP command information or data. The peripheral uses this signal to
flow control in the forward direction. It is an "interlocked" handshake
with nStrobe. PeriphAck also provides command information in the
reverse direction.

PError
(nAckReverse)

Used to acknowledge a change in the direction the transfer (asserted =
forward). The peripheral drives this signal low to acknowledge
nReverseRequest. It is an "interlocked" handshake with
nReverseRequest. The host relies upon nAckReverse to determine
when it is permitted to drive the data bus.

Select

Indicates printer on line.

nAutoFd
(HostAck)

Requests a byte of data from the peripheral when asserted,
handshaking with nAck in the reverse direction. In the forward direction
this signal indicates whether the data lines contain ECP address or
data. The host drives this signal to flow control in the reverse direction.
It is an "interlocked" handshake with Ack. HostAck also provides
command information in the forward phase.

nFault
(nPeriphRequest)

Generates an error interrupt when asserted. This signal provides a
mechanism for peer-to-peer communication. This signal is valid only in
the forward direction. During ECP Mode the peripheral is permitted
(but not required) to drive this pin low to request a reverse transfer. The
request is merely a "hint" to the host; the host has ultimate control over
the transfer direction. This signal would be typically used to generate
an interrupt to the host CPU.

nInit

Sets the transfer direction (asserted = reverse, deasserted = forward).
This pin is driven low to place the channel in the reverse direction. The
peripheral is only allowed to drive the bi-directional data bus while in
ECP Mode and HostAck is low and nSelectIn is high.

nSelectIn

Always deasserted in ECP mode.

103

Register Definitions

The register definitions are based on the
standard IBM addresses for LPT. All of the
standard printer ports are supported. The
additional registers attach to an upper bit
decode of the standard LPT port definition to

avoid conflict with standard ISA devices. The
port is equivalent to a generic parallel port
interface and may be operated in that mode.
The port registers vary depending on the mode
field in the ecr. The table below lists these
dependencies. Operation of the devices in
modes other that those specified is undefined.

Table 42 - ECP Register Definitions

NAME

ADDRESS (Note 1)

ECP MODES

FUNCTION

data

+000h R/W

000-001

Data Register

ecpAFifo

+000h R/W

011

ECP FIFO (Address)

dsr

+001h R/W

All

Status Register

dcr

+002h R/W

All

Control Register

cFifo

+400h R/W

010

Parallel Port Data FIFO

ecpDFifo

+400h R/W

011

ECP FIFO (DATA)

tFifo

+400h R/W

110

Test FIFO

cnfgA

+400h R

111

Configuration Register A

cnfgB

+401h R/W

111

Configuration Register B

ecr

+402h R/W

All

Extended Control Register

Note 1: These addresses are added to the parallel port base address as selected by configuration

Note 2: All addresses are qualified with AEN. Refer to the AEN pin definition.

Table 43 - Mode Descriptions

MODE

DESCRIPTION*

000

SPP mode

001

PS/2 Parallel Port mde

010

Parallel Port Data FIFO mode

011

ECP Parallel Port mode

100

EPP mode (If this option is enabled in the configuration registers)

101

(Reserved)

110

Test mode

111

Configuration mode

*Refer to ECR Register Description

104

DATA and ecpAFifo PORT
ADDRESS OFFSET = 00H

Modes 000 and 001 (Data Port)

The Data Port is located at an offset of '00H'
from the base address. The data register is
cleared at initialization by RESET. During a
WRITE operation, the Data Register latches the
contents of the data bus on the rising edge of
the nIOW input. The contents of this register
are buffered (non inverting) and output onto the
PD0 - PD7 ports. During a READ operation,
PD0 - PD7 ports are read and output to the host
CPU.

Mode 011 (ECP FIFO - Address/RLE)

A data byte written to this address is placed in
the FIFO and tagged as an ECP Address/RLE.
The hardware at the ECP port transmitts this
byte to the peripheral automatically. The
operation of this register is ony defined for the
forward direction (direction is 0). Refer to the
ECP Parallel Port Forward Timing Diagram,
located in the Timing Diagrams section of this
data sheet .

DEVICE STATUS REGISTER (dsr)
ADDRESS OFFSET = 01H

The Status Port is located at an offset of '01H'
from the base address. Bits 0 - 2 are not
implemented as register bits, during a read of
the Printer Status Register these bits are a low
level. The bits of the Status Port are defined as
follows:

BIT 3 nFault
The level on the nFault input is read by the CPU
as bit 3 of the Device Status Register.

BIT 4 Select
The level on the Select input is read by the CPU
as bit 4 of the Device Status Register.

BIT 5 PError
The level on the PError input is read by the CPU
as bit 5 of the Device Status Register. Printer
Status Register.

BIT 6 nAck
The level on the nAck input is read by the CPU
as bit 6 of the Device Status Register.

BIT 7 nBusy
The complement of the level on the BUSY input
is read by the CPU as bit 7 of the Device Status
Register.

DEVICE CONTROL REGISTER (dcr)
ADDRESS OFFSET = 02H

The Control Register is located at an offset of
'02H' from the base address. The Control
Register is initialized to zero by the RESET
input, bits 0 to 5 only being affected; bits 6 and
7 are hard wired low.

BIT 0 STROBE - STROBE
This bit is inverted and output onto the
nSTROBE output.

BIT 1 AUTOFD - AUTOFEED
This bit is inverted and output onto the
nAUTOFD output. A logic 1 causes the printer
to generate a line feed after each line is printed.
A logic 0 means no autofeed.

BIT 2 nINIT - nINITIATE OUTPUT
This bit is output onto the nINIT output without
inversion.

BIT 3 SELECTIN
This bit is inverted and output onto the nSLCTIN
output. A logic 1 on this bit selects the printer; a
logic 0 means the printer is not selected.

BIT 4 ackIntEn - INTERRUPT REQUEST
ENABLE
The interrupt request enable bit when set to a
high level may be used to enable interrupt
requests from the Parallel Port to the CPU due

105

to a low to high transition on the nACK input.
Refer to the description of the interrupt under
Operation, Interrupts.

BIT 5 DIRECTION
If mode=000 or mode=010, this bit has no effect
and the direction is always out regardless of the
state of this bit. In all other modes, Direction is
valid and a logic 0 means that the printer port is
in output mode (write); a logic 1 means that the
printer port is in input mode (read).

Bits 6 and 7 during a read are a low level, and
cannot be written.

cFifo (Parallel Port Data FIFO)
ADDRESS OFFSET = 400h
Mode = 010

Bytes written or DMAed from the system to this
FIFO are transmitted by a hardware handshake
to the peripheral using the standard parallel port
protocol. Transfers to the FIFO are byte
aligned. This mode is only defined for the
forward direction.

ecpDFifo (ECP Data FIFO)
ADDRESS OFFSET = 400H
Mode = 011

Bytes written or DMAed from the system to this
FIFO, when the direction bit is 0, are transmitted
by a hardware handshake to the peripheral
using the ECP parallel port protocol. Transfers
to the FIFO are byte aligned.

Data bytes from the peripheral are read under
automatic hardware handshake from ECP into
this FIFO when the direction bit is 1. Reads or
DMAs from the FIFO will return bytes of ECP
data to the system.

tFifo (Test FIFO Mode)
ADDRESS OFFSET = 400H
Mode = 110
Data bytes may be read, written or DMAed to or
from the system to this FIFO in any direction.
Data in the tFIFO will not be transmitted to the
to the parallel port lines using a hardware
protocol handshake. However, data in the
tFIFO may be displayed on the parallel port data
lines.

The tFIFO will not stall when overwritten or
underrun. If an attempt is made to write data to
a full tFIFO, the new data is not accepted into
the tFIFO. If an attempt is made to read data
from an empty tFIFO, the last data byte is re-
read again. The full and empty bits must
always keep track of the correct FIFO state. The
tFIFO will transfer data at the maximum ISA
rate so that software may generate performance
metrics.

The FIFO size and interrupt threshold can be
determined by writing bytes to the FIFO and
checking the full and serviceIntr bits.

The writeIntrThreshold can be derermined by
starting with a full tFIFO, setting the direction bit
to 0 and emptying it a byte at a time until
serviceIntr is set. This may generate a
spurious interrupt, but will indicate that the
threshold has been reached.

The readIntrThreshold can be derermined by
setting the direction bit to 1 and filling the empty
tFIFO a byte at a time until serviceIntr is set.
This may generate a spurious interrupt, but will
indicate that the threshold has been reached.

106

Data bytes are always read from the head of
tFIFO regardless of the value of the direction bit.
For example if 44h, 33h, 22h is written to the
FIFO, then reading the tFIFO will return 44h,
33h, 22h in the same order as was written.

cnfgA (Configuration Register A)
ADDRESS OFFSET = 400H
Mode = 111

This register is a read only register. When read,
10H is returned. This indicates to the system
that this is an 8-bit implementation. (PWord = 1
byte)

cnfgB (Configuration Register B)
ADDRESS OFFSET = 401H
Mode = 111

BIT 7 compress
This bit is read only. During a read it is a low
level. This means that this chip does not
support hardware RLE compression. It does
support hardware de-compression!

BIT 6 intrValue
Returns the value on the ISA iRq line to
determine possible conflicts.

BITS 5:0 Reserved
During a read are a low level. These bits cannot
be written.

ecr (Extended Control Register)
ADDRESS OFFSET = 402H
Mode = all

This register controls the extended ECP parallel
port functions.

BITS 7,6,5
These bits are Read/Write and select the Mode.

BIT 4 nErrIntrEn
Read/Write (Valid only in ECP Mode)
1:

Disables the interrupt generated on the
asserting edge of nFault.

Enables an interrupt pulse on the high to
low edge of nFault. Note that an interrupt
will be generated if nFault is asserted
(interrupting) and this bit is written from a 1
to a 0. This prevents interrupts from being
lost in the time between the read of the ecr
and the write of the ecr.

BIT 3 dmaEn
Read/Write
1:

Enables DMA (DMA starts when serviceIntr
is 0).

Disables DMA unconditionally.

BIT 2 serviceIntr
Read/Write
1:

Disables DMA and all of the service
interrupts.

Enables one of the following 3 cases of
interrupts. Once one of the 3 service
interrupts has occurred serviceIntr bit shall
be set to a 1 by hardware, it must be reset
to 0 to re-enable the interrupts. Writing this
bit to a 1 will not cause an interrupt.

case dmaEn=1:

During DMA (this bit is set to a 1 when
terminal count is reached).

case dmaEn=0 direction=0:

This bit shall be set to 1 whenever there are
writeIntrThreshold or more bytes free in the
FIFO.

case dmaEn=0 direction=1:

This bit shall be set to 1 whenever there are
readIntrThreshold or more valid bytes to be
read from the FIFO.

BIT 1 full
Read only
1:

The FIFO cannot accept another byte or the
FIFO is completely full.

The FIFO has at least 1 free byte.

BIT 0 empty
Read only
1:

The FIFO is completely empty.

The FIFO contains at least 1 byte of data.

107

Table 44 - Extended Control Register

R/W

MODE

000:

Standard Parallel Port mode . In this mode the FIFO is reset and common collector drivers
are used on the control lines (nStrobe, nAutoFd, nInit and nSelectIn). Setting the direction
bit will not tri-state the output drivers in this mode.

001:

PS/2 Parallel Port mode. Same as above except that direction may be used to tri-state the
data lines and reading the data register returns the value on the data lines and not the
value in the data register. All drivers have active pull-ups (push-pull).

010:

Parallel Port FIFO mode. This is the same as 000 except that bytes are written or DMAed to
the FIFO. FIFO data is automatically transmitted using the standard parallel port protocol.
Note that this mode is only useful when direction is 0. All drivers have active pull-ups
(push-pull).

011:

ECP Parallel Port Mode. In the forward direction (direction is 0) bytes placed into the
ecpDFifo and bytes written to the ecpAFifo are placed in a single FIFOand transmitted
automatically to the peripheral using ECP Protocol. In the reverse direction (direction is1)
bytes are moved from the ECP parallel port and packed into bytes in the ecpDFifo. All
drivers have active pull-ups (push-pull).

100:

Selects EPP Mode: In this mode, EPP is selected if the EPP supported option is selected in
configuration register CR4. All drivers have active pull-ups (push-pull).

101:

Reserved

110:

Test Mode. In this mode the FIFO may be written and read, but the data will not be
transmitted on the parallel port. All drivers have active pull-ups (push-pull).

111:

Configuration Mode. In this mode the confgA, confgB registers are accessible at 0x400 and
0x401. All drivers have active pull-ups (push-pull).

108

OPERATION

Mode Switching/Software Control

Software will execute P1284 negotiation and all
operation prior to a data transfer phase under
programmed I/O control (mode 000 or 001).
Hardware provides an automatic control line
handshake, moving data between the FIFO and
the ECP port only in the data transfer phase
(modes 011 or 010).

Setting the mode to 011 or 010 will cause the
hardware to initiate data transfer.

If the port is in mode 000 or 001 it may switch to
any other mode. If the port is not in mode 000
or 001 it can only be switched into mode 000 or
001. The direction can only be changed in
mode 001.

Once in an extended forward mode the software
should wait for the FIFO to be empty before
switching back to mode 000 or 001. In this case
all control signals will be deasserted before the
mode switch. In an ecp reverse mode the
software waits for all the data to be read from
the FIFO before changing back to mode 000 or
001. Since the automatic hardware ecp reverse
handshake only cares about the state of the
FIFO it may have acquired extra data which will
be discarded. It may in fact be in the middle of a
transfer when the mode is changed back to 000
or 001. In this case the port will deassert
nAutoFd independent of the state of the transfer.
The design shall not cause glitches on the
handshake signals if the software meets the
constraints above.

ECP Operation

Prior to ECP operation the Host must negotiate
on the parallel port to determine if the peripheral
supports the ECP protocol. This is a somewhat
complex negotiation carried out under program
control in mode 000.

After negotiation, it is necessary to initialize
some of the port bits. The following are required:

Set Direction = 0, enabling the drivers.

Set strobe = 0, causing the nStrobe signal
to default to the deasserted state.

Set autoFd = 0, causing the nAutoFd signal
to default to the deasserted state.

Set mode = 011 (ECP Mode)

ECP address/RLE bytes or data bytes may be
sent automatically by writing the ecpAFifo or
ecpDFifo respectively.

Note that all FIFO data transfers are byte wide
and byte aligned. Address/RLE transfers are
byte-wide and only allowed in the forward
direction.

The host may switch directions by first switching
to mode = 001, negotiating for the forward or
reverse channel, setting direction to 1 or 0,
then setting mode = 011. When direction is 1
the hardware shall handshake for each ECP
read data byte and attempt to fill the FIFO.
Bytes may then be read from the ecpDFifo as
long as it is not empty .

ECP transfers may also be accomplished (albeit
slowly) by handshaking individual bytes under
program control in mode = 001, or 000.

Termination from ECP Mode

Termination from ECP Mode is similar to the
termination from Nibble/Byte Modes. The host is
permitted to terminate from ECP Mode only in
specific well-defined states. The termination can
only be executed while the bus is in the forward
direction. To terminate while the channel is in
the reverse direction, it must first be transitioned
into the forward direction.

109

Command/Data

ECP Mode supports two advanced features to
improve the effectiveness of the protocol for
some applications. The features are
implemented by allowing the transfer of normal
8-bit data or 8-bit commands.

When in the forward direction, normal data is
transferred when HostAck is high and an 8-bit
command is transferred when HostAck is low.

The most significant bit of the command
indicates whether it is a run-length count (for
compression) or a channel address.

When in the reverse direction, normal data is
transferred when PeriphAck is high and an 8-bit
command is transferred when PeriphAck is low.
The most significant bit of the command is
always zero. Reverse channel addresses are
seldom used and may not be supported in
hardware.

Table 45

Forward Channel Commands (HostAck Low)

Reverse Channel Commands (PeripAck Low)

D[6:0]

Run-Length Count (0-127)
(mode 0011 0X00 only)

Channel Address (0-127)

Data Compression

The FDC37C665GT/666GT supports run length
encoded (RLE) decompression in hardware and
can transfer compressed data to a peripheral.
Run length encoded (RLE) compression in
hardware is not supported. To transfer
compressed data in ECP mode, the
compression count is written to the ecpAFifo
and the data byte is written to the ecpDFifo.

Compression is accomplished by counting
identical bytes and transmitting an RLE byte
that indicates how many times the next byte is
to be repeated. Decompression simply
intercepts the RLE byte and repeats the
following byte the specified number of times.
When a run-length count is received from a
peripheral, the subsequent data byte is
replicated the specified number of times. A
run-length count of zero specifies that only one
byte of data is represented by the next data
byte, whereas a run-length count of 127

indicates that the next byte should be expanded
to 128 bytes. To prevent data expansion,
however, run-length counts of zero should be
avoided.

Pin Definition

The drivers for nStrobe, nAutoFd, nInit and
nSelectIn are open-collector in mode 000 and
are push-pull in all other modes.

ISA Connections

The interface can never stall causing the host to
hang. The width of data transfers is strictly
controlled on an I/O address basis per this
specification. All FIFO-DMA transfers are byte
wide, byte aligned and end on a byte boundary.
(The PWord value can be obtained by reading
Configuration Register A, cnfgA, described in
the next section.) Single byte wide transfers

110

are always possible with standard or PS/2
mode using program control of the control
signals.

Interrupts

The interrupts are enabled by serviceIntr in the
ecr register.

serviceIntr = 1 Disables the DMA and all of the

service interrupts.

serviceIntr = 0Enables the selected interrupt

condition. If the interrupting
condition is valid, then the
interrupt is generated
immediately when this bit is
changed from a 1 to a 0. This
can occur during Programmed
I/O if the number of bytes
removed or added from/to the
FIFO does not cross the
threshold.

The interrupt generated is ISA friendly in that it
must pulse the interrupt line low, allowing for
interrupt sharing. After a brief pulse low
following the interrupt event, the interrupt line is
tri-stated so that other interrupts may assert.

An interrupt is generated when:

1. For DMA transfers: When serviceIntr is 0,

dmaEn is 1 and the DMA TC is received.

2. For Programmed I/O:

When serviceIntr is 0, dmaEn is 0,
direction is 0 and there are
writeIntrThreshold or more free bytes in
the FIFO. Also, an interrupt is
generated when serviceIntr is cleared
to 0 whenever there are
writeIntrThreshold or more free bytes in
the FIFO.

(1)

When serviceIntr is 0, dmaEn
is 0, direction is 1 and there
are readIntrThreshold or more
bytes in the FIFO. Also, an
interrupt is generated when
serviceIntr is cleared to 0
whenever there are
readIntrThreshold or more
bytes in the FIFO.

3. When nErrIntrEn is 0 and nFault transitions

from high to low or when nErrIntrEn is set
from 1 to 0 and nFault is asserted.

4. When ackIntEn is 1 and the nAck signal

transitions from a low to a high.

FIFO Operation

The FIFO threshold is set in the chip
configuration registers. All data transfers to or
from the parallel port can proceed in DMA or
Programmed I/O (non-DMA) mode as indicated
by the selected mode. The FIFO is used by
selecting the Parallel Port FIFO mode or ECP
Parallel Port Mode. (FIFO test mode will be
addressed separately.) After a reset, the FIFO
is disabled. Each data byte is transferred by a
Programmed I/O cycle or PDRQ depending on
the selection of DMA or Programmed I/O mode.

The following paragraphs detail the operation of
the FIFO flow control. In these descriptions,
<threshold> ranges from 1 to 16. The
parameter FIFOTHR, which the user programs,
is one less and ranges from 0 to 15.

A low threshold value (i.e. 2) results in longer
periods of time between service requests, but
requires faster servicing of the request for both
read and write cases. The host must be very
responsive to the service request. This is the
desired case for use with a "fast" system.

111

A high value of threshold (i.e. 12) is used with a
"sluggish" system by affording a long latency
period after a service request, but results in
more frequent service requests.

DMA TRANSFERS

DMA transfers are always to or from the
ecpDFifo, tFifo or CFifo. DMA utilizes the
standard PC DMA services. To use the DMA
transfers, the host first sets up the direction and
state as in the programmed I/O case. Then it
programs the DMA controller in the host with the
desired count and memory address. Lastly it
sets dmaEn to 1 and serviceIntr to 0. The ECP
requests DMA transfers from the host by
activating the PDRQ pin. The DMA will empty
or fill the FIFO using the appropriate direction
and mode. When the terminal count in the DMA
controller is reached, an interrupt is generated
and serviceIntr is asserted, disabling DMA. In
order to prevent possible blocking of refresh
requests dReq shall not be asserted for more
than 32 DMA cycles in a row. The FIFO is
enabled directly by asserting nPDACK and
addresses need not be valid. PINTR is
generated when a TC is received. PDRQ must
not be asserted for more than 32 DMA cycles in
a row. After the 32nd cycle, PDRQ must be
kept unasserted until nPDACK is deasserted for
a minimum of 350nsec. (Note: The only way to
properly terminate DMA transfers is with a TC.)

DMA may be disabled in the middle of a transfer
by first disabling the host DMA controller. Then
setting serviceIntr to 1, followed by setting
dmaEn to 0, and waiting for the FIFO to
become empty or full. Restarting the DMA is
accomplished by enabling DMA in the host,
setting dmaEn to 1, followed by setting
serviceIntr to 0.

DMA Mode - Transfers from the FIFO to the
Host

(Note: In the reverse mode, the peripheral may
not continue to fill the FIFO if it runs out of data

to transfer, even if the chip continues to request
more data from the peripheral.)

The ECP activates the PDRQ pin whenever
there is data in the FIFO. The DMA controller
must respond to the request by reading data
from the FIFO. The ECP will deactivate the
PDRQ pin when the FIFO becomes empty or
when the TC becomes true (qualified by
nPDACK), indicating that no more data is
required. PDRQ goes inactive after nPDACK
goes active for the last byte of a data transfer
(or on the active edge of nIOR, on the last byte,
if no edge is present on nPDACK). If PDRQ
goes inactive due to the FIFO going empty, then
PDRQ is active again as soon as there is one
byte in the FIFO. If PDRQ goes inactive due to
the TC, then PDRQ is active again when there
is one byte in the FIFO, and serviceIntr has
been re-enabled. (Note: A data underrun may
occur if PDRQ is not removed in time to prevent
an unwanted cycle.)

Programmed I/O Mode or Non-DMA Mode

The ECP or parallel port FIFOs may also be
operated using interrupt driven programmed I/O.
Software can determine the writeIntrThreshold,
readIntrThreshold, and FIFO depth by accessing
the FIFO in Test Mode.

Programmed I/O transfers are to the ecpDFifo
at 400H and ecpAFifo at 000H or from the
ecpDFifo located at 400H, or to/from the tFifo at
400H. To use the programmed I/O transfers,
the host first sets up the direction and state, sets
dmaEn to 0 and serviceIntr to 0.

The ECP requests programmed I/O transfers
from the host by activating the PINTR pin. The
programmed I/O will empty or fill the FIFO using
the appropriate direction and mode.

Note: A threshold of 16 is equivalent to a
threshold of 15. These two cases are treated
the same.

112

Programmed I/O - Transfers from the FIFO to
the Host

In the reverse direction an interrupt occurs when
serviceIntr is 0 and readIntrThreshold bytes
are available in the FIFO. If at this time the
FIFO is full it can be emptied completely in a
single burst, otherwise readIntrThreshold bytes
may be read from the FIFO in a single burst.

readIntrThreshold =(16-<threshold>) data bytes

in FIFO

An interrupt is generated when serviceIntr is 0
and the number of bytes in the FIFO is greater
than or equal to (16-<threshold>). (If the
threshold = 12, then the interrupt is set
whenever there are 4-16 bytes in the FIFO.) The
PINT pin can be used for interrupt-driven
systems. The host must respond to the request
by reading data from the FIFO. This process is
repeated until the last byte is transferred out of
the FIFO. If at this time the FIFO is full, it can
be completely emptied in a single burst,
otherwise a minimum of (16-<threshold>) bytes
may be read from the FIFO in a single burst.

Programmed I/O - Transfers from the Host to
the FIFO

In the forward direction an interrupt occurs when
serviceIntr is 0 and there are writeIntrThreshold
or more bytes free in the FIFO. At this time if
the FIFO is empty it can be filled with a single
burst before the empty bit needs to be re-read.
Otherwise it may be filled with
writeIntrThreshold bytes.

writeIntrThreshold = (16-<threshold>)

free bytes in FIFO

An interrupt is generated when serviceIntr is 0
and the number of bytes in the FIFO is less than
or equal to <threshold>. (If the threshold = 12,
then the interrupt is set whenever there are 12 or
less bytes of data in the FIFO.) The PINT pin
can be used for interrupt-driven systems. The
host must respond to the request by writing data
to the FIFO. If at this time the FIFO is empty, it
can be completely filled in a single burst,
otherwise a minimum of (16-<threshold>) bytes
may be written to the FIFO in a single burst.
This process is repeated until the last byte is
transferred into the FIFO.

113

INTEGRATED DRIVE ELECTRONICS INTERFACE

The IDE interface enables hard disks with
embedded controllers (AT and XT) to be
interfaced to the host processor. The following
definitions are for reference only. These
registers are not implemented in the
FDC37C665GT and FDC37C666GT. Access to
these registers are controlled by the
FDC37C665GT and FDC37C666GT. For more
information, refer to the IDE pin descriptions
and the ATA specification.

HOST FILE REGISTERS

The HOST FILE REGISTERS are accessed by
the AT Host, rather than the Local Processor.
There are two groups of registers, the AT Task
File, and the Miscellaneous AT Registers.

ADDRESS 1F0H-1F7H; 170H-177H

These AT registers contain the Task File
Registers. These registers communicate data,
command, and status information with the AT
host, and are addressed when nHDCS0 is low.

ADDRESS 376H/3F6H; 377H/3F7H

These AT registers may be used by the BIOS for
drive control. They are accessed by the AT
interface when nHDSC1 is active.

Figure 3 shows the AT Host Register Map of the
FDC37C665GT and FDC37C666GT.

FIGURE 3 - HOST PROCESSOR REGISTER ADDRESS MAP (AT MODE)

PRIMARY

SECONDARY

1F0H

1F7H

170H

177H

TASK FILE REGISTERS

3F6H

3F7H

376H

377H

MISC. AT REGISTERS

TASK FILE REGISTERS

Task File Registers may be accessed by the
host AT when pin nHDCS0 is active (low). The
Data Register (1F0H) is 16 bits wide; the
remaining task file registers are 8 bits wide. The
task file registers are ATA and EATA

compatible. Please refer to the ATA and EATA
specifications. These are available from:

Global Engineering
2805 McGaw Street
Irvine, CA 92714
(800) 854-7179
(714) 261-1455

117

CONFIGURATION

The configuration of the FDC37C665GT within
the user system is selected through software
selectable configuration registers. The different
configurations of the FDC37C666GT can be
selected through a combination of jumper
options and software.

FDC37C665GT CONFIGURATION
REGISTERS

The configuration registers are used to select
programmable options of the FDC. After power
up, the FDC is in the default mode. The default
modes are identified in the Configuration Mode
Register Description. To program the
configuration registers, the following sequence
must be followed:

1.Enter Configuration Mode.
2.Configure FDC Registers.
3.Exit Configuration Mode.

Enter Configuration Mode

To enter the configuration mode of the
FDC37C665GT, two writes in succession to port
3F0H with 55H data are required. If a write to
another address or port occurs

between these two writes, the chip does not
enter the configuration mode. It is strongly
recommended that interrupts be disabled for the
duration of these two writes.

Configure FDC37C665GT

The FDC37C665GT contains SIXTEEN
configuration registers, CR0-CRF. These
registers are accessed by first writing the
number (0-F) of the desired register to port
3F0H and then writing or reading the
configuration register through port 3F1H.

Exit Configuration Mode

The configuration mode is exited by writing an
AAH to port 3F0H.

Programming Example

The following is an example of a configuration
program in Intel 8086 assembly language. For
this example, the FDC37C665GT is being reset
to the default condition after power up.

119

Table 46 - FDC37C665GT Configuration Registers

Default

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

3BH

CR0

VALID

OSC

FDC EN

FDC PWR

(RESERVED)

IDE AT/XT

IDE EN

9FH

CR1

LOCK CRx

COM3, 4 ADDR

IRQ POL

PP MODE

PP PWR

Parallel Port Address

DCH

CR2

UART2 PWR

UART2

UART2 ADDRESS

UART1

PWR

UART1 EN

UART1 ADDRESS

78H

CR3

ADRx/

DRV2 EN/

PINTR

IDENT

MFM

DRIVE OPTIONS

PINTR

ENHANCED

FDC MODE

(RESERVED)

00H

CR4

(RESERVED)

EPP Type

MIDI 2

MIDI 1

Parallel Port FDC

PP EXT MODES

00H

CR5

(RESERVED)

EXTx4

DRV 0X1

DEN SEL

DMA MODE

IDE SEC

FDC SEC

FFH

CR6

Floppy Drive D

Floppy Drive C

Floppy Drive B

Floppy Drive A

00H

CR7

RESERVED

Media ID Polarity

Floppy Boot Drive

00H

CR8

ADR7

ADR6

ADR5

ADR4

ADR3

ADR2

ADR1

ADR0

00H

CR9

RESERVED

ADR10

ADR9

ADR8

00H

CRA

RESERVED

ECP FIFO THRESHOLD

TBD

CRB

RESERVED

TBD

CRC

RESERVED

66/65H

CRD

1/0

0/1

01H

CRE

00H

CRF

TEST MODES - RESERVED

FDC37C665GT Configuration Register
Description

The configuration registers consist of seventeen
registers, the Configuration Select Register and
Configuration Registers 0-F. The configuration
select register is written to by writing to port
3F0H. The Configuration Registers 0-F are
accessed by reading or writing to port 3F1H.

Configuration Select Register (CSR)

This register can only be accessed when the
FDC is in the Configuration Mode. This register,
located at port 3F0H, must be

initialized upon entering the Configuration Mode
before the configuration registers (CR0-CRF)
can be accessed and is used to select which of
the Configuration Registers are to be accessed
at port 3F1H.

Configuration Registers 0-F

These registers are set to their default values at
power up and are not affected by RESET. They
are accessed at port 3F1H. Refer to the
following descriptions for the function of each
configuration register.

120

CR0

This register can only be accessed when the
FDC is in the Configuration Mode and after the
CSR has been initialized to 00H. The default

value of this register after power up is 3BH for
the FDC37C665GT and 2BH for the
FDC37C666GT.

Table 47 - CR0

BIT NO.

BIT NAME

DESCRIPTION

IDE ENABLE

A high level on this bit, enables the IDE (Default). A low level on
this bit disables the IDE.

IDE AT/XT

A high level on this bit sets the IDE to AT type (Default). A low
level on this bit sets the IDE to XT type.

RESR

(This bit is Reserved - set to '0').

FDC POWER

A high level on this bit, supplies power to the FDC (Default). A
low level on this bit puts the FDC in low power mode.

FDC ENABLE

A high level on this bit, enables the FDC (Default for
FDC37C665GT). A low level on this bit disables the FDC
(Default for FDC37C665GT).

5,6

OSC

6 5
0 0 Osc ON, Baud Rate Generator (BRG) Clock Enabled.
0 1 Osc is On, BRG Clock is ON when PWRGD is active. When
PWRGD is inactive, Osc is off and BRG Clock is Disabled
(Default).
1 0 (same as 0 1 case)
1 1 Osc OFF, BR Generator Clock Disabled

VALID

A high level on this software controlled bit indicates that a valid
configuration cycle has occurred. The control software must take
care to set this bit at the appropriate times. Set to zero after
power up.

121

CR1

This register can only be accessed when the
FDC is in the Configuration Mode and after the

CSR has been initialized to 01H. The default
value of this register after power up is 9FH.

Table 48 - CR1

BIT NO.

BIT NAME

DESCRIPTION

0,1

Parallel Port
Address

These bits are used to select the Parallel Port Address.
1 0 Parallel Port Address
0 0 Disabled
0 1 3BCH
1 0 378H
1 1 278H (Default)

Parallel Port
Power

A high level on this bit, supplies power to the Parallel Port
(Default). A low level on this bit puts the Parallel Port in low
power mode.

Parallel Port
Mode

Parallel Port Mode. A high level on this bit, sets the Parallel Port
for Printer Mode (Default). A low level on this bit enables the
Extended Parallel port modes. Refer to Bits 0 and 1 of CR4

IRQ Polarity

A high level on this bit, programs IRQ3, IRQ4, FINTR and
(PINTR) for active high, inactive low (Default). A low level on
this bit programs IRQ3, IRQ4, FINTR and (PINTR) for active
low, inactive hi-Z. (See Note CR1_1)

5,6

COM3,4

Select the COM3 and COM4 address.

6 5 COM3 COM4
0 0 338H 238H (Default)
0 1 3E8H 2E8H
1 0 2E8H 2E0H
1 1 220H 228H

LOCK CRx

A high level on this bit enables the reading and writing of CR0-
CRF (Default). A low level on this bit disables the reading and
writing of CR0-CRF. Once set to 0, this bit can only be set to 1
by a hard reset or power-up reset.

Note CR1_1: If the parallel port is configured for ECP or EPP modes, then PINTR is always active

low, inactive hi-z independent of this bit.

122

CR2

This register can only be accessed when the
FDC is in the Configuration Mode and after the

CSR has been initialized to 02H. The default
value of this register after power up is DCH.

Table 49 - CR2

BIT NO.

BIT NAME

DESCRIPTION

0,1

UART 1 Address
Select

These bits select the Primary Serial Port Address.
1 0 COM Port ADDRESS
0 0 COM1 3F8H (Default)
0 1 COM2 2F8H
1 0 COM3 (Refer to CR1, bits 5,6)
1 1 COM4 (Refer to CR1, bits 5,6)

UART 1 Enable

A high level on this bit, enables the Primary Serial Port (Default).
A low level on this bit disables the Primary Serial Port.

UART 1 Power
down

A high level on this bit, allows normal operation of the Primary
Serial Port (Default). A low level on this bit places the Primary
Serial Port into Power Down Mode.

4,5

UART 2 Address
Select

These bits select the Secondary Serial Port Address.
5 4 COM Port ADDRESS
0 0 COM1 3F8H
0 1 COM2 2F8H (Default)
1 0 COM3 (Refer to CR1, bits 5,6)
1 1 COM4 (Refer to CR1, bits 5,6)

UART 2 Enable

A high level on this bit enables the Secondary Serial Port
(Default). A low level on this bit disables the Secondary Serial
Port.

UART 2 Power
down

A high level on this bit, allows normal operation of the Secondary
Serial Port (Default). A low level on this bit places the Secondary
Serial Port into Power Down Mode.

123

CR3

This register can only be accessed when the
FDC is in the Configuration Mode and the

CSR has been initialized to 03H. The default
value after power up is 78H.

Table 50 - CR3

BIT NO.

BIT NAME

DESCRIPTION

RESERVED

Reserved - Read as zero

Enhanced
Floppy Mode
2

Bit 1

Floppy Mode - Refer to the description of the TAPE
DRIVE REGISTER (TDR) for more information on
these modes.

NORMAL Floppy Mode (Default)

Enhanced Floppy Mode 2 (OS2)

Drive Opt 0

These two bits control the DRATE0 and DRATE1 outputs. The mapping
from the DRATE SEL bit of the DSR, DIR AND CCR to the DRATE
outputs is shown in Table 50 below. Defaults 1, 1 after power-up. If bit
1 = 1, then bits 3 and 4 become "don't cares".

Drive Opt 1

MFM

IDENT is used in conjunction with MFM to define the interface mode of
operation.

IDENT

IDENT

1
1
0
0

MFM

1
0
1
0

MODE
AT Mode (Default)
Reserved
PS/2
Model 30

7,2

ADRx/
DRV2 EN/
PINTR

Bit 7

0
1
1

Bit 2

0
1

Pin 94

Input DRV2

ADDRX
PINTR2

Pin 39
PINTR
PINTR
High-Z

ADRx output/DRIVE 2 EN input: When set to a 1, this bit enables the
output. When cleared to a 0 (default) this bit allows the connection of the
Drive 2 indicator. Drive 2 is not available for the FDC37C666GT

125

CR4

This register can only be accessed when the
FDC is in the Configuration Mode and the

CSR has been initialized to 04H. The default
value after power up is 00H.

Table 52 - CR4 - Parallel and Serial Extended Setup Register

BIT NO.

BIT NAME

DESCRIPTION

1,0

Parallel Port
Extended Modes

Bit 1

Bit 0

If CR1 bit 3 is a low level then:

Standard and Bidirectional Modes (SPP)
(Default)

EPP Mode and SPP

ECP Mode (Note CR4_2)

ECP Mode & EPP Mode (Note CR4_1, 2)

2,3

Parallel Port
FDC

Refer to Parallel Port Floppy Disk Controller description.

Bit 3

Bit 2

Normal

PPFD1

PPFD2

Reserved

MIDI 1

Serial Clock Select Port 1: A low level on this bit, disables MIDI
support, clock = divide by 13 (Default). A high level on this bit
enables MIDI support, clock = divide by 12. (Note CR4_3)

MIDI 2

Serial Clock Select Port 2: A low level on this bit, disables MIDI
support, clock = divide by 13 (Default). A high level on this bit
enables MIDI support, clock = divide by 12. (Note CR4_3)

EPP Type

0 = EPP 1.9 (Default)
1 = EPP 1.7

RESR

(This bit is Reserved - set/read as '0').

Note CR4_1: In this mode, EPP can be selected through the ecr register of ECP as mode 100.
Note CR4_2: In these modes, 2 drives can be supported directly, 3 or 4 drives must use external 4

drive support! SPP can be selected through the ecr register of ECP as mode 000.

Note CR4_3: MIDI Support: The Musical Instrumental Digital Interface (MIDI) operates at 31.25Kbaud

(+/-1%) which can be derived from 125KHz. (24MHz/12=2MHz, 2MHz/16=125KHz).

126

CR5

This register can only be accessed when the
FDC is in the Configuration Mode and the

CSR has been initialized to 05H. The default
value after power up is 00H.

Table 53 - CR5- Floppy Disk and IDE Extended Setup Register

BIT NO.

BIT NAME

DESCRIPTION

FDC Secondary

A low level on this bit selects the primary address for the FDC
interface (Default). A high level on this bit selects the secondary
address space.

IDE Secondary

A low level on this bit selects the primary address for the IDE
interface (Default). A high level on this bit selects the secondary
address space.

FDC DMA Mode

0=(default) Burst mode is enabled for the FDC FIFO execution
phase data transfers. 1=Non-Burst mode enabled. The FDRQ
and FIRQ pins are strobed once for each byte transferred while
the FIFO is enabled.

4,3

DenSel

Bit 4

Bit 3

Densel output

Normal (Default)

Reserved

swap drv 0,1

A high level on this bit, swaps drives and motor sel 0 and 1 of the
FDC. A low level on this bit does not (Default).

EXTx4

External 4 drive support: 0=Internal 4 drive decoder (default).
1=External 4 drive decoder (External 2 to 4 decoder required).

DS3

Set to 0 (default) - Pin 98 is DS2 if ECP is not enabled by the
configuration or PDIR if ECP is enabled.
Set to 1 - Pin 98 is DS3 regardless of the parallel port mode.

ADDRESS

BLOCK NAME

NOTES

3F0-3F7

Floppy Disk

Primary address

370-377

Floppy Disk

Secondary address

1F0-1F7, 3F6,3F7

IDE

Primary address

170-177, 376,377

IDE

Secondary address

127

CR6
This register can only be accessed when the
FDC is in the Configuration Mode and after the
CSR has been initialized to 06H. The default
value of this register after power up is FFH. This
register holds the floppy disk drive types for up
to four floppy disk drives.

CR7
This register can only be accessed when the
FDC is in the Configuration Mode and after the
CSR has been initialized to 07H. The default
value of this register after power up is 00H. This
register holds the value for the floppy boot drive
and the polarity of the media ID bits.

CR8
This register can only be accessed when the
FDC is in the Configuration Mode and after the
CSR has been initialized to 08H. The default
value of this register after power up is 00H. This
is the lower 8 bits for the ADRx address decode.
(Note: All addresses are qualified with AEN.)

CR9
This register can only be accessed when the
FDC is in the Configuration Mode and after the
CSR has been initialized to 09H. The default
value of this register after power up is 00H. This
is the upper 3 bits (D2 - MSB, D0 - LSB) for the
ADRx address decode. If ECP mode is not
selected then A10 is assumed to be low. (Note:
All addresses are qualified with AEN.)

CRA
This register can only be accessed when the
FDC is in the Configuration Mode and after the
CSR has been initialized to 0AH. The default
value of this register after power up is 00H. This
byte defines the FIFO threshold for the ECP
mode parallel port.

CRB and CRC
Reserved - The contents of these registers are
undefined when read.

CRD
This register can only be accessed when the
FDC is in the Configuration Mode and after the
CSR has been initialized to 0DH. This register
is read only. The default value of this register
after power up is 065H for the FDC37C665GT
and a 066H for the FDC37C666GT.

CRE
This register can only be accessed when the
FDC is in the Configuration Mode and after the
CSR has been initialized to 0EH. This register
is read only. The default value of this register
after power up is 02H. This is used to identify
the chip revision level.

CRF
This register can only be accessed when the
FDC is in the Configuration Mode and after the
CSR has been initialized to 0FH. The default
value of this register after power up is 00H.

128

Table 54 - CRF

BIT NO.

BIT NAME

DESCRIPTION

Test 0

Reserved - Set to zero.

Test 1

Reserved - Set to zero.

Test 2

Reserved - Set to zero.

Test 3

Reserved - Set to zero.

Test 4

Reserved - Set to zero.

Test 5

Reserved - Set to zero.

Test 6

Reserved - Set to zero.

Test 7

Reserved - Set to zero.

FDC37C666GT Hardware Configuration

The FDC37C666GT hardware configuration can
select or deselect the parallel, serial, FDC

and IDE circuits, FDC and IDE addresses, set
the parallel port and serial port addresses and
move the configuration register addresses.

PCF1

PCF0

PARALLEL PORT ADDRESS

Disabled

3BCH

378H

278H

ECPEN

PADCF

PARALLEL PORT MODE

Printer Mode (output only)

EPP

ECP

ECP+EPP

129

S1CF1

S1CF0

PRIMARY SERIAL PORT ADDRESS

Disabled

COM3 3E8H

COM2 2F8H

COM1 3F8H

S2CF1

S2CF0

SECONDARY SERIAL PORT ADDRESS

Disabled

COM4 2E8H

COM1 3F8H

COM2 2F8H

IDECF

IDEACF

IDE CONTROL

Disabled

Reserved

Primary

Secondary

FDCCF

FACF

FDC CONTROL

Floppy Disabled, Configuration registers at 3F0H and 3F1H and allow
override of FDC enable/disable and primary/secondary address in config
registers. DRATEx power-up as inputs, allow selection of Enhanced
Floppy Mode 2.

Floppy Disabled, Configuration registers at 370H and 371H and allow
override of FDC enable/disable and primary/secondary address in config
registers. DRATEx power-up as inputs, allow selection of Enhanced
Floppy Mode 2.

FDC at Primary Address (DRATE0,1 are outputs, Enhanced Floppy Mode
2 not available)

FDC at Secondary Address (DRATE0,1 are outputs, Enhanced Floppy
Mode 2 not available)

130

FDC37C666GT Software Configuration -
Differences from FDC37C665GT

All software configuration options available for
the FDC37C665GT are available for the
FDC37C666GT except for those options
selected by the hardware configuration pins. The
options set by hardware configuration in the
FDC37C666GT that cannot be changed by
software are:

Parallel Port Address (set by PCF1, PCF0)
Parallel Port Mode (Set by ECPEN and PADCF)
Serial Port Address (Set by S1CF1, S1CF0,
S2CF1, S2CF0)
IDE Control (Set by IDECF, IDEACF)
FDC Control (if FDCCF=1, Set by FACF, If
FDCCF=0 can be changed in software
configuration)

The location of the configuration select registers

(CSR) can be moved to 370H and the
configuration registers 0-F can be accessed at
port 371H by setting FDCCF=0 and FACF=1.

To enter the configuration mode of the
FDC37C666GT, two writes in succession to the
CSR (port 3F0H or 370H see FDCCF and
FACF) with 44H data are required. If a write to
another address or port occurs between these
two writes, the chip does not enter the
configuration mode. It is strongly recommended
that interrupts be disabled for the duration of
these two writes. The configuration mode is
exited by writing an AAH to the CSR.

In the FDC37C666GT, the pins used to
configure the part should be connected as per
the diagram below. This shows how a jumper
can be used to set a high (VCC) or a low (GND)
into the port for configuration at the end of the
reset pulse.

27k ohms

To FDC37C666GT

VCC

GND

131

OPERATIONAL DESCRIPTION

MAXIMUM GUARANTEED RATINGS*

Operating Temperature Range......................................................................................... 0

C to +70

Storage Temperature Range..........................................................................................-55

to +150

Lead Temperature Range (soldering, 10 seconds) .................................................................... +325

Positive Voltage on any pin, with respect to Ground ................................................................V

+0.3V

Negative Voltage on any pin, with respect to Ground.................................................................... -0.3V
Maximum V

................................................................................................................................. +7V

*Stresses above those listed above could cause permanent damage to the device. This is a stress
rating only and functional operation of the device at any other condition above those indicated in the
operation sections of this specification is not implied.

Note: When powering this device from laboratory or system power supplies, it is important that the
Absolute Maximum Ratings not be exceeded or device failure can result. Some power supplies exhibit
voltage spikes on their outputs when the AC power is switched on or off. In addition, voltage
transients on the AC power line may appear on the DC output. If this possibility exists, it is suggested
that a clamp circuit be used.

DC ELECTRICAL CHARACTERISTICS (T

= 0

C - 70

C, V

= +5.0 V ± 10%)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

COMMENTS

I Type Input Buffer

Low Input Level

High Input Level

ILI

IHI

2.0

0.8

TTL Levels

IS Type Input Buffer

Low Input Level

High Input Level

Schmitt Trigger Hysteresis

ILIS

IHIS

HYS

2.2

250

0.8

Schmitt Trigger

CLK

Input Buffer

Low Input Level

High Input Level

ILCK

IHCK

3.0

0.4

Input Leakage
(All I and IS buffers except
PWRGD)
Low Input Leakage

High Input Leakage

-10

+10

= 0

= V

132

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

COMMENTS

Input Current
PWRGD

150

= 0

I/O24 Type Buffer

Low Output Level

High Output Level

Output Leakage

2.4

-10

0.5

+10

= 24 mA

= -12 mA

= 0 to V

(Note 1)

O24 Type Buffer

Low Output Level

High Output Level

Output Leakage

2.4

-10

0.5

+10

= 24 mA

= -12 mA

= 0 to V

(Note 1)

OD24 Type Buffer

Low Output Level

Output Leakage

-10

0.5

+10

= 24 mA

= 0 to V

(Note 1)

OD24P Type Buffer

Low Output Level

High Output Level

Output Leakage

2.4

-10

0.5

+10

= 24 mA

= -30

= 0 to V

(Note 1)

OP24 Type Buffer

Low Output Level

High Output Level

Output Leakage

2.4

-10

0.5

+10

= 24 mA

= -4 mA

= 0 to V

(Note 1)

OD48 Type Buffer

Low Output Level

Output Leakage

-10

0.5

+10

= 48 mA

= 0 to V

(Note 2)

133

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

COMMENTS

O4 Type Buffer

Low Output Level

High Output Level

Output Leakage

2.4

-10

0.4

+10

= 4 mA

= -1 mA

= 0 to V

(Note 1)

O8 Type Buffer

Low Output Level

High Output Level

Output Leakage

2.4

-10

0.4

+10

= 8 mA

= -4 mA

= 0 to V

(Note 1)

Supply Current Active

Supply Current Standby

CSBY

300

500

All outputs open.

Note 3

ChiProtect
(SLCT, PE, BUSY, nACK,
nERROR)

±10

Chip in circuit:
V

= 0V

= 6V Max.

Backdrive
(nSTROBE, nAUTOFD,
nINIT,nSLCTIN)

±10

= 0V

= 6V Max.

Backdrive
(PD0-PD7)

±10

= 0V

= 6V Max.

Note 1: All output leakages are measured with the current pins in high impedance as defined by the

PWRGD pin (FDC37C665GT only).

Note 2: Output leakage is measured with the low driving output off, either for a high level output or a

high impedance state defined by PWRGD (FDC37C665GT only).

Note 3: Defined by the device configuration with the PWRGD input low.

CAPACITANCE T

= 25

C; fc = 1MHz; V

= 5V

PARAMETER

SYMBOL

LIMITS

UNIT

TEST CONDITION

MIN

TYP

MAX

Clock Input Capacitance

All pins except pin
under test tied to
AC ground

Input Capacitance

Output Capacitance

OUT

136

nDACK Delay Time from FDRQ High
DRQ Reset Delay from nIOR or nIOW
FDRQ Reset Delay from nDACK Low
nDACK Width
nIOR Delay from FDRQ High
nIOW Delay from FDRQ High
Data Access Time from nIOR Low
Data Set Up Time to nIOW High
Data to Float Delay from nIOR High
Data Hold Time from nIOW High
nDACK Set Up to nIOW/nIOR Low
nDACK Hold After nIOW/nIOR High
TC Pulse Width
AEN Set Up to nIOR/nIOW
AEN Hold from nDACK
TC Active to PDRQ Inactive

Parameter

min

typ

max

units

t1
t2
t3
t4
t5
t6
t7
t8
t9

t10
t11
t12
t13
t14
t15
t16

150

0
0

40
10
10

10
60
40
10

100
100

100

ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns

t15

t12

t16

t11

t14

t10

t13

AEN

FDRQ,
PDRQ

nDACK

nIOR

nIOW

DATA

(DO-D7)

DATA VALID

FIGURE 6 - DMA TIMING

140

t10

t11

AEN,

nIOCS16

A0-A9

nIDEENLO,

nIDEENHI,

nGAMECS,

HDCSx

IDED7

nIOR

DB7

nIOW

IDED7

t3
t4
t5
t6
t7
t8
t9

t10
t11

nIDEENLO, nIDEENHI, nGAMECS, nHDCSx
Delay from AEN, IOCS16
nIDEENLO, nIDEENHI, nGAMECS, nHDCSx
Delay from A0-A9
IDED7 Hold Time after nIOR
DB7 Delay from nIOR
DB7 Hold Time from nIOR
DB7 Hold Time from nIOW
IDED7 Delay from Data Bus nIOW Active
IDED7 Inactive Delay from nIOW
nIDEENLO Delay from nIDEENHI,
nIOCS16, AEN
IDED7 Set Up Time before nIOR
IDED7 Delay from DB7, IDED7 in Output
Mode

Parameter

min

typ

max

units

10
10

60
60

50
50
40

ns
ns
ns
ns
ns
ns
ns
ns

ns
ns

FIGURE 11 - IDE INTERFACE TIMING

142

t18

t17

t12

t19

t10

t11

t13

t20

t22

t14

t16

t15

t21

A0-A10

SD<7:0>

nIOW

IOCHRDY

nWRITE

PD<7:0>

nDATAST

nADDRSTB

nWAIT

PDIR

t1
t2
t3
t4
t5
t6
t7
t8
t9

t10
t11
t12
t13
t14
t15
t16
t17
t18
t19
t20
t21
t22

nIOW Asserted to PDATA Valid
nWAIT Asserted to nWRITE Change
nWRITE to Command Asserted
nWAIT Deasserted to Command Deasserted
nWAIT Asserted to PDATA Invalid
Time Out
Command Deasserted to nWAIT Asserted
SDATA Valid to nIOW Asserted
nIOW Deasserted to DATA Invalid
nIOW Asserted to IOCHRDY Asserted
nWAIT Deasserted to IOCHRDY Deasserted
IOCHRDY Deasserted to nIOW Deasserted
nIOW Asserted to nWRITE Asserted
nWAIT Asserted to Command Asserted
Command Asserted to nWAIT Deasserted
PDATA Valid to Command Asserted
Ax Valid to nIOW Asserted
nIOW Deasserted to Ax Invalid
nIOW Deasserted to nIOW or nIOR Asserted
nWAIT Asserted to nWRITE Asserted
nWAIT Asserted to PDIR Low
PDIR Low to nWRITE Asserted

ns
ns
ns
ns
ns
µs
ns
ns
ns
ns
ns
ns
ns
ns
µs
ns
ns
ns
ns
ns
ns
ns

185

190

160

210

185

Parameter

min

max

units

0
0

60
10

10
40
10
40
60

0
0

Notes

1
1

1. WAIT must be filtered to compensate for ringing on the parallel bus cable. WAIT is considered to have settled after it
does not transition for a minimum of 50 nsec.

FIGURE 13 - EPP 1.9 DATA OR ADDRESS WRITE CYCLE

144

t1
t2
t3

t4
t5
t6
t7
t8
t9

t10

t11

t12

t13
t14
t15
t16
t17
t18
t19
t20
t21
t22
t23
t24
t25
t26
t27
t28

PDATA Hi-Z to Command Asserted
nIOR Asserted to PDATA Hi-Z
nWAIT Deasserted to Command
Deasserted
Command Deasserted to PDATA Hi-Z
Command Asserted to PDATA Valid
PDATA Hi-Z to nWAIT Deasserted
PDATA Valid to nWAIT Deasserted
nIOR Assertd to IOCHRDY Asserted
nWRITE Deasserted to nIOR Asserted
nWAIT Deasserted to IOCHRDY
Deasserted
IOCHRDY Deasserted to nIOR
Deasserted
nIOR Deasserted to SDATA Hi-Z (Hold
Time)
PDATA Valid to SDATA Valid
nWAIT Asserted to Command Asserted
Time Out
nWAIT Deasserted to PDATA Driven
nWAIT Deasserted to nWRITE Modified
SDATA Valid to IOCHRDY Deasserted
Ax Valid to nIOR Asserted
nIOR Deasserted to Ax Invalid
nWAIT Asserted to nWRITE Deasserted
nIOR Deasserted to nIOW or nIOR Asserted
nWAIT Asserted to PDIR Set
PDATA Hi-Z to PDIR Set
nWAIT Asserted to PDATA Hi-Z
PDIR Set to Command
nWAIT Deasserted to PDIR Low
nWRITE Deasserted to Command

ns
ns
ns

ns
ns
µs
ns
ns
ns
ns

ns
ns
µs
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns

30
50

180

160

195

190
190

185

180

Parameter

min

max

units

0
0

0
0
0
0
0
0

0
0

10
60
60

40
10

40
60

Notes

2
1

1,2

1. nWAIT is considered to have settled after it does not transition for a minimum of 50 ns.
2. When not executing a write cycle, EPP nWRITE is inactive high.
3. 85 is true only if t7 = 0.

FIGURE 14B - EPP 1.9 DATA OR ADDRESS READ CYCLE TIMING PARAMETERS

145

t18

t17

t12

t19

t10

t20

t11

t13

t16

t21

A0-A10

SD<7:0>

nIOW

IOCHRDY

nWRITE

PD<7:0>

nDATAST

nADDRSTB

nWAIT

PDIR

nIOW Asserted to PDATA Valid
Command Dessserted to nWRITE Change
nWRITE to Command
nIOW Deasserted to Command Deasserted
Command Deasserted to PDATA Invalid
Time Out
SDATA Valid to nIOW Asserted
nIOW Deasserted to DATA Invalid
nIOW Asserted to IOCHRDY Asserted
nWAIT Deasserted to IOCHRDY Deasserted
IOCHRDY Deasserted to nIOW Deasserted
nIOW Asserted to nWRITE Asserted
PDATA Valid to Command Asserted
Ax Valid to nIOW Asserted
nIOW Deasserted to Ax Invalid
nIOW Deasserted to nIOW or nIOR Asserted
nWAIT Asserted to IOCHRDY Deasserted
Command Deasserted to nWAIT Deasserted

ns
ns
ns
ns
ns
µs
ns
ns
ns
ns
ns
ns
ns
ns
µs
ns
ns
ns

50
40
35
50

24
40

50
35

Parameter

min

max

units

0
0
5

50
10
10

0
0

10
40
10

100

Notes

1. WRITE is controlled by clearing the PDIR bit to "0" in the control register before
performing an EPP Write.
2. This number is only valid if WAIT is active when IOW goes active.

t1
t2
t3
t4
t5
t6
t8
t9

t10
t11
t12
t13
t16
t17
t18
t19
t20
t21

FIGURE 15 - EPP 1.7 DATA OR ADDRESS WRITE CYCLE

146

t20

t19

t11

t15

t22

t13

t12

t10

t23

t21

A0-A10

nIOR

SD<7:0>

IOCHRDY

nWRITE

PD<7:0>

nDATASTB

nADDRSTB

nWAIT

PDIR

t2
t3
t4
t5
t8

t10
t11
t12
t13
t15
t19
t20
t21
t22
t23

nIOR Deasserted to Command Deasserted
nWAIT Asserted to IOCHRDY Deasserted
Command Deasserted to PDATA Hi-Z
Command Asserted to PDATA Valid
nIOR Asserted to IOCHRDY Asserted
nWAIT Deasserted to IOCHRDY Deasserted
IOCHRDY Deasserted to nIOR Deasserted
nIOR Deasserted to SDATA High-Z (Hold Time)
PData Valid to SDATA Valid
Time Out
Ax Valid to nIOR Asserted
nIOR Deasserted to Ax Invalid
Command Deasserted to nWAIT Deasserted
nIOR Deasserted to nIOW or nIOR Asserted
nIOR Asserted to Command Asserted

ns
ns
ns
ns
ns
ns
ns
ns
ns
µs
ns
ns
ns
ns
ns

50
40

24
50

40
40
12

Parameter

min

max

units

0
0
0

0
0

10
40
10

Notes

1. WRITE is controlled by setting the PDIR bit to "1" in the control register before
performing an EPP Read.

FIGURE 16 - EPP 1.7 DATA OR ADDRESS READ CYCLE

147

ECP PARALLEL PORT TIMING

Parallel Port FIFO (Mode 101)

The standard parallel port is run at or near the
peak 500Kbytes/sec allowed in the forward
direction using DMA. The state machine does
not examine nAck and begins the next transfer
based on Busy. Refer to Figure 17.

ECP Parallel Port Timing

The timing is designed to allow operation at
approximately 2.0Mbytes/sec over a 15ft cable.
If a shorter cable is used then the bandwidth will
increase.

Forward-Idle

When the host has no data to send it keeps
HostClk (nStrobe) high and the peripheral will
leave PeriphClk (Busy) low.

Forward Data Transfer Phase

The interface transfers data and commands
from the host to the peripheral using an
interlocked PeriphAck and HostClk. The
peripheral may indicate its desire to send data
to the host by asserting nPeriphRequest.

The Forward Data Transfer Phase may be
entered from the Forward-Idle Phase. While in
the Forward Phase the peripheral may
asynchronously assert the nPeriphRequest
(nFault) to request that the channel be reversed.
When the peripheral is not busy it sets
PeriphAck (Busy) low. The host then sets
HostClk (nStrobe) low when it is prepared to
send data. The data must be stable for the
specified setup time prior to the falling edge of
HostClk. The peripheral then sets PeriphAck
(Busy) high to acknowledge the handshake. The
host then sets HostClk (nStrobe) high. The
peripheral then accepts the data and sets

PeriphAck (Busy) low, completing the transfer.
This sequence is shown in Figure 18.

The timing is designed to provide 3 cable
round-trip times for data setup if Data is driven
simultaneously with HostClk (nStrobe).

Reverse-Idle Phase

The peripheral has no data to send and keeps
PeriphClk high. The host is idle and keeps
HostAck low.

Reverse Data Transfer Phase

The interface transfers data and commands
from the peripheral to the host using an
interlocked HostAck and PeriphClk.

The Reverse Data Transfer Phase may be
entered from the Reverse-Idle Phase. After the
previous byte has beed accepted the host sets
HostAck (nAutoFd) low. The peripheral then sets
PeriphClk (nAck) low when it has data to send.
The data must be stable for the specified setup
time prior to the falling edge of PeriphClk. When
the host is ready it to accept a byte it sets.
HostAck (nAutoFd) high to acknowledge the
handshake. The peripheral then sets PeriphClk
(nAck) high. After the host has accepted the
data it sets HostAck (nAutoFd) low, completing
the transfer. This sequence is shown in Figure
19.

Output Drivers

To facilitate higher performance data transfer,
the use of balanced CMOS active drivers for
critical signals (Data, HostAck, HostClk,
PeriphAck, PeriphClk) are used ECP Mode.
Because the use of active drivers can present
compatibility problems in Compatible Mode (the
control signals, by tradition, are specified as

148

open-collector), the drivers are dynamically
changed from open-collector to totem-pole. The
timing for the dynamic driver change is specified
in the IEEE 1284 Extended Capabilities Port
Protocol and ISA Interface

Standard, Rev. 1.09, Jan. 7, 1993, available
from Microsoft. The dynamic driver change
must be implemented properly to prevent
glitching the outputs.

PDATA

nSTROBE

BUSY

Parameter

min

max

units

t1
t2
t3
t4
t5
t6

DATA Valid to nSTROBE Active
nSTROBE Active Pulse Width
DATA Hold from nSTROBE Inactive
nSTROBE Active to BUSY Active
BUSY Inactive to nSTROBE Active
BUSY Inactive to PDATE Invalid

600
600
450

680

ns
ns
ns
ns
ns
ns

500

Notes

1. The data is held until BUSY goes inactive or for time t3, whichever is longer. This only
applies if another data transfer is pending. If no other data transfer is pending, the data
is held indefinitely.

FIGURE 17 - PARALLEL PORT FIFO TIMING

149

Parameter

min

max

units

t1
t2
t3

t4
t5
t6

nAUTOFD Valid to nSTROBE Asserted
PDATA Valid to nSTROBE Asserted
BUSY Deasserted to nAUTOFD
Changed
BUSY Deasserted to PDATA Changed
nSTROBE Asserted to BUSY Asserted
nSTROBE Deasserted to Busy
Deasserted
BUSY Deasserted to nSTROBE
Asserted
BUSY Asserted to nSTROBE
Deasserted

0
0

ns
ns
ns

60
60

180

200

180

Notes

1,2

1. Maximum value only applies if there is data in the FIFO waiting to be written out.
2. BUSY is not considered asserted or deasserted until it is stable for a minimum of 75 to
130 ns.

nAUTOFD

PDATA<7:0>

nSTROBE

BUSY

FIGURE 18 - ECP PARALLEL PORT FORWARD TIMING

151

0.10

-C-

TD/TE

DIM

A1
A2

e
0

TD(1)
TE(1)
TD(2)
TE(2)

MIN
2.80

0.1

2.57
23.4
19.9
17.4
13.9

0.1

0.65

1.8

MAX

3.15
0.45
2.87

24.15

20.1

18.15

14.1

0.2

0.95

2.6

MIN
.110
.004
.101
.921
.783
.685
.547
.004
.026
.071

MAX

.124
.018
.113
.951
.791
.715
.555
.008
.037
.102

0°

21.8
15.8

22.21
16.27

12°

22.2
16.2

22.76
16.82

0.65 BSC

0°

.008
.858
.622
.874
.641

12°

.016
.874
.638
.896
.662

.0256 BSC

Notes:
1) Coplanarity is 0.100mm (.004") maximum.
2) Tolerance on the position of the leads is
0.200mm (.008") maximum.
3) Package body dimensions D1 and E1 do not
include the mold protrusion. Maximum mold
protrusion is 0.25mm (.010").
4) Dimensions TD and TE are important for testing
by robotic handler. Only above combinations of (1)
or (2) are acceptable.
5) Controlling dimension: millimeter. Dimensions
in inches for reference only and not necessarily
accurate.

MILLIMETERS

INCHES

FIGURE 20 - 100 PIN QFP

STANDARD MICROSYSTEMS CORP.

Circuit diagrams utilizing SMSC products are included as a means of illustrating typical
applications; consequently complete information sufficient for construction purposes is
not necessarily given. The information has been carefully checked and is believed to be
entirely reliable. However, no responsibility is assumed for inaccuracies. Furthermore,
such information does not convey to the purchaser of the semiconductor devices
described any licenses under the patent rights of SMSC or others. SMSC reserves the
right to make changes at any time in order to improve design and supply the best
product possible. SMSC products are not designed, intended, authorized or warranted
for use in any life support or other application where product failure could cause or
contribute to personal injury or severe property damage. Any and all such uses without
prior written approval of an Officer of SMSC and further testing and/or modification will
be fully at the risk of the customer.

FDC37C665GT/FDC37C666GT Rev. 11/28/94

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: FDC37C665GT

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: FDC37C665GT