TC1068

TC1068-1 2/8/99

SMBus Thermal Sensor with External Diode Input

FEATURES

Backward Compliant to Older APM Systems

Includes Internal and External Sensing Capability

Outputs Temperature As 8-Bit Digital Word

Solid State Temperature Sensing; 1

C Resolution

3.0 5.5V Operating Range

Independent Internal and External Threshold
Set-Points With ALERT#/COMP# Interrupt Output

SMBus 2-Wire Serial Interface

Up To Nine TC1068s May Share the Same Bus

Standby Mode for Low Standby Power

Low Power .......................... 70

A (max) Operating

...................................... 10

A (max) Standby Mode

16-Pin Plastic QSOP Package

TYPICAL APPLICATIONS

Thermal Protection For Intel "Deschutes"
PentiumTMII and Other High Performance CPUs
with Integrated On-Board Diode -- No Sensor
Mounting Problems!

Accurate Thermal Sensing From Any Si
Junction Diode

Thermal Management in Electronic Systems:
Computers, Network Equipment, Power Supplies

GENERAL DESCRIPTION

The TC1068 is a serially programmable temperature

sensor optimized for monitoring modern high performance
CPUs with on-board integrated thermal diodes. Tempera-
ture data is converted from the CPU's thermal diode outputs
and made available as an 8-bit digital word.

Communication with the TC1068 is accomplished via

the standard System Management Bus (SMBus) commonly
used in modern computer systems. This permits reading the
current internal/external temperature, programming the
threshold setpoints, and configuring the device. Addition-
ally, an interrupt is generated on the ALERT#/COMP# pin
when temperature moves outside the preset threshold win-
dows in either direction.

A Standby command may be sent via the SMBus or by

signaling the STBY# input pin to activate the low-power
Standby mode. Registers can be accessed while in Standby
mode. Address selection inputs allow up to nine TC1068s to
share the same 2-wire SMBus for multi-zone monitoring.

All registers can be read by the host, and both polled and

interrupt driven systems are easily accommodated. Small
size, low installed cost, and ease of use make the TC1068
an ideal choice for implementing sophisticated system man-
agement schemes, such as ACPI.

ORDERING INFORMATION

Part No.

Package

Temp. Range

TC1068MQR

QSOP-16

C to +125

TCM1617EV

Evaluation Kit Available

BLOCK DIAGRAM

EVALUATION

KIT

AVAILABLE

PIN CONFIGURATION

Register Set

Modulator

Control

Logic

SMBus

Interface

ALERT#/COMP#

STBY#

SCL

SDA

ADD 0

ADD 1

Ext. Temp

Status Byte

Config. Byte

Conv. Rate

Ext. Hi Limit

Ext. Lo Limit

Int. Hi Limit

Int. Lo Limit

Int. Temp

Internal

Sensor

(Diode)

INT_SEL

16-Pin Plastic QSOP

INT_SEL

GND

SCL

STBY#

SDA

ALERT#/COMP#

ADD0

D+

TC1068

ADD 1

SMBus Thermal Sensor with

External Diode Input

TC1068

TC1068-1 2/8/99

ABSOLUTE MAXIMUM RATINGS*

Power Supply Voltage (V

) ......................................... 6V

Voltage On Any Pin ............ (GND 0.3V) to (V

+ 0.3V)

Operating Temperature (T

) .................. 55

C to +125

Storage Temperature (T

STG

) .................. 65

C to +150

SMBus Input/Output Current ................. 1 mA to +50 mA
D Input Current ......................................................

1 mA

*Static-sensitive device. Unused devices must be stored in conductive
material. Protect devices from static discharge and static fields. Stresses
above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. These are stress ratings only and functional
operation of the device at these or any other conditions above those
indicated in the operational sections of the specifications is not implied.
Exposure to Absolute Maximum Rating Conditions for extended periods
may affect device reliability.

DC ELECTRICAL CHARACTERISTICS:

= 3.3V, 55

125

C, unless otherwise noted.

Symbol

Parameter

Test Conditions

Min

Typ

Max

Unit

Power Supply

Power Supply Voltage

+125

3.0

5.5

UV-LOCK

Undervoltage

2.4

2.80

2.95

Lockout Threshold

POR

Power-On Reset Threshold

Falling Edge

1.0

1.7

2.3

Operating Current

0.25 Conv./Sec Rate

SMBus Inactive (Note 1)

Operating Current

2 Conv./Sec Rate

180

SMBus Inactive (Note 1)

DD-STANDBY

Standby Supply Current

= 3.3V SMBus Active

100

DD-STANDBY

Standby Supply Current

= 3.3V, SMBus Inactive

ADD-BIAS

ADD[1:0] Bias Current

Power-Up Only

160

ALERT#/COMP# Output

Output Low Voltage

= 1.0 mA (Note 3)

0.4

ADD[1:0]

Logic Input Low

x 0.3

Logic Input High

x 0.7

STBY# Input

Logic Input Low

x .3

Logic Input High

x .7

INT_SEL

Logic Input Low

x .3

Logic Input High

x .7

Internal Pull-up Resistance

500

Temp-to-Bits Converter

RES

Basic Temperature Resolution

IERR1

Internal Diode Temperature

+60

+100

+125

< 0

EERR

External Diode Temperature

+60

+100

(Note 4)

+125

< 0

TC1068

SMBus Thermal Sensor with
External Diode Input

TC1068-1 2/8/99

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

DIODE-HIGH

External Diode

(D+) (D) ~ 0.65V

100

High Source Current

DIODE-LOW

External Diode

(D+) (D) ~ 0.65V

Low Source Current

D-SOURCE

D Source Voltage

0.7

CONV

Conversion Time

From CHIP STOP to Conv.

112

msec

Complete (Note 2)

Conversion Rate Accuracy

See Conversion Rate Register Desc.

+35

2-Wire SMBus Interface

Logic Input High

2.2

Logic Input Low

0.8

SDA Output Low

= 2 mA (Note 3)

0.4

= 4 mA (Note 3)

0.6

Input Capacitance SDA, SCL

LEAK

I/O Leakage

0.1

NOTES: 1. Operating current is an average value (including external diode injection pulse current) integrated over multiple conversion cycles. Transient

current may exceed this specification.

2. For true reccurring conversion time see Conversion Rate register description.
3. Output current should be minimized for best temperature accuracy. Power dissipation within the TC1068 will cause self-heating and

temperature drift error.

4. Refer to Application Note 64.

SMBus PORT AC TIMING:

= 3.3V, 55

= T

)

125

C; C

= 80 pF, unless otherwise noted.

Symbol

Parameter

Test Conditions

Min

Typ

Max

Unit

SMB

SMBus Clock Frequency

100

KHz

LOW

Low Clock Period

10% to 10%

4.7

sec

HIGH

High Clock Period

90% to 90%

sec

SMBus Rise Time

10% to 90%

1,000

nsec

SMBus Fall Time

90% to 10%

300

nsec

SU(START)

Start Condition Setup Time

90% SCL to 10% SDA

sec

(for Repeated Start Condition)

H(START)

Start Condition Hold Time

sec

SU-DATA

Data in Setup Time

1000

nsec

H-DATA

Data in Hold Time

1250

nsec

SU(STOP)

Stop Condition Setup Time

sec

IDLE

Bus Free Time Prior to

4.7

sec

New Transition

ELECTRICAL CHARACTERISTICS (CONT):

= 3.3V, 55

125

C,unless otherwise noted.

SMBus Thermal Sensor with

External Diode Input

TC1068

TC1068-1 2/8/99

SMBUS Read Timing Diagram

TIMING DIAGRAMS

tSU(START) tH(START)

tSU-DATA

tH-DATA

tSU(STOP) tIDLE

A = Start Condition

B = MSB of Address Clocked into Slave

C = LSB of Address Clocked into Slave

D = R/W Bit Clocked into Slave

E = Slave Pulls SDA Line Low

F = Acknowledge Bit Clocked into Master

G = MSB of Data Clocked into Slave

H = LSB of Data Clocked into Slave

I = Slave Pulls SDA Line Low

J = Acknowledge Clocked into Master

K = Acknowledge Clock Pulse

L = Stop Condition, Data Executed by Slave

M = New Start Condition

ILOW

IHIGH

SCL

SDA

tSU(START)

tH(START)

tSU-DATA

tSU(STOP)

tIDLE

A = Start Condition

B = MSB of Address Clocked into Slave

C = LSB of Address Clocked into Slave

D = R/W Bit Clocked into Slave

E = Slave Pulls SDA Line Low

F = Acknowledge Bit Clocked into Master

G = MSB of Data Clocked into Master

H = LSB of Data Clocked into Master

ILOW

IHIGH

I = Acknowledge Clock Pulse

J = Stop Condition

K = New Start Condition

SCL

SDA

SMBUS Writing Timing Diagram

TC1068

SMBus Thermal Sensor with
External Diode Input

TC1068-1 2/8/99

PIN DESCRIPTION

Pin Number

Symbol

Type

Description

Power

Power Supply Input

D+

Bi-Directional

Current Source and A/D Positive Input

Bi-Directional

Current Sink and A/D Negative Input

6,10

ADD[1:0]

Input

Address Select Pins (See Address Decode Table)

7,8

GND

Power

System Ground

ALERT#/COMP#

Output

SMBus Interrupt (SMBALERT#) or Comparator Output

SDA

Bi-Directional

SMBus Serial Data

SCL

Input

SMBus Serial Clock

STBY#

Input

Standby Enable

INT_SEL

Input

Selects ALERT# or COMP# Output on Pin 11

1, 5, 9, 16

Not Connected

PIN DESCRIPTION

SCL

Input. SMBus serial clock. Clocks data into and out of

the TC1068. See System Management Bus Specification,
rev. 1.0, for timing diagrams.

SDA

Bidirectional. Serial data is transferred on the SMBus in

both directions using this pin. See System Management Bus
Specification, rev. 1.0, for timing diagrams.

ADD1, ADD0

Inputs.

Sets the 7-bit SMBus address. These pins are

"tri-state," and the SMBus addresses are specified in the
Address Decode Table.

(NOTE: The tri-state scheme allows up to nine TC1068s

on a single bus. A match between the TC1068's address and
the address specified in the serial bit stream must be made
to initiate communication. Many SMBus-compatible devices
with other addresses may share the same 2-wire bus (see
System Management Bus Specification, rev. 1.0, for ad-
dress allocations). These pins are only active at power-on
reset, and will latch into the appropriate states.

ALERT#/COMP#*

Output, Open Collector, Active Low. The ALERT# out-

put corresponds to the general SMBALERT# signal and
indicates an interrupt event. The TC1068 will respond to the
standard SMBus Alert Response Address (see SMBus
Specification 1.0) and associated protocol when ALERT# is
asserted. Normally, the ALERT# output will be asserted and
latched when any of the following occurs:

1. INT_TEMP equal to or exceeds INT_HLIM
2. INT_TEMP below INT_LLIM
3. EXT_TEMP equal to or exceeds EXT_HLIM
4. EXT_TEMP below EXT_LLIM
5. External Diode "Open"

The operation of the ALERT# output is controlled by the

MASK1 bit in the CONFIG register. If the MASK1 bit is set to
"1," no interrupts will be generated on ALERT#. The ALERT#
output is cleared and rearmed by the Alert Response Ad-
dress (ARA). This output may be WIRE-ORed with similar
outputs from other SMBus devices. If the alarm condition
persists after the ARA, the ALERT# output will be immedi-
ately re-asserted.

(NOTE: A pull-up resistor is necessary on ALERT#

since it is an open-drain output. Current sourced from the
pull-up resistor causes power dissipation and may cause
internal heating of the TC1068. To avoid affecting the
accuracy of internal temperature readings, the pull-up resis-
tors should be made as large as possible.)

Normally the COMP# output will be asserted upon the

following events:

1. EXT_TEMP equal to or exceeds EXT_HLIM
2. External Diode "Open"

COMP# will be de-asserted upon the following event:

EXT_TEMP below EXT_HLIM.

The operation of the COMP# output is controlled by the

MASK1 bit in the CONFIG register. If the MASK1 bit is set to
"1," no interrupts will be generated on COMP#. This output
may be WIRE-ORed with similar outputs from other SMBus
devices. Note: A pull-up resistor is necessary on COMP#
since it is an open-drain output. Current sourced from the

SMBus Thermal Sensor with

External Diode Input

TC1068

TC1068-1 2/8/99

pull-up resistor causes power dissipation and may cause
internal heating of the TC1068. To avoid affecting the
accuracy of internal temperature readings, the pull-up resis-
tors should be made as large as possible. *Pin 11's function
is selected with pin 13 (INT_SEL) -- see INT_SEL.

INT_SEL

Input. The operation of Pin 11 is defined by the state

of this pin. There is an internal pull-up to V

. If INT_SEL

is high, Pin 11 will function as ALERT#. If INT_SEL is
grounded, Pin 11 will function as COMP#

STBY#

Input. The activation of Standby mode may be achieved

using either the STBY# pin or the CHIP STOP bit (CONFIG
register). If STBY# is pulled low, the TC1068 unconditionally
enters its low-power Standby mode (I

= 10

A, max). The

temperature-to-digital conversion process is halted, but
ALERT# and OS# remain functional. The TC1068's bus
interface remains active, and all registers may be read from
and written to normally. The INT_TEMP and EXT_TEMP
registers will contain whatever data was valid at the time of
Standby. (Transitions on SDA or SCL due to external bus
activity may increase the Standby power consumption.)

D+

Bi-directional. This pin connects to the anode of the

external diode and is the positive A/D input. Current is
injected into the external diode from the TC1068, and the
temperature proportional V

is measured and converted to

digital temperature data.

Bi-directional. This pin connects to the cathode of the

external diode. Current is sunk from the external diode into
the TC1068 through this pin. It also is the negative input
terminal to the TC1068's A/D converter. This node is kept at
approximately 0.7V above GROUND.

Input. Power supply input. See electrical specifications.

GND

Input. Ground return for all TC1068 functions.

FUNCTIONAL DESCRIPTION

The TC1068 acquires and converts temperature infor-

mation from two separate sources, both silicon junction
diodes, with a basic accuracy of

C. One is located on the

TC1068 die; the other is connected externally. This external
diode may be located on another IC die. The analog-to-
digital converter on the TC1068 alternately converts tem-
perature data from the two sensors and stores them sepa-
rately in internal registers.

The system interface is a slave SMBus port with an

ALERT# (SMBALERT#) and COMP# interrupt outputs. The
ALERT# interrupt is triggered when one or more of four
preset temperature thresholds are tripped (see Figure 1).
These four thresholds are user-programmable via the SMBus
port. The COMP# interrupt is triggered when EXT_TEMP
equals or exceeds EXT_HLIM. Additionally, the tempera-
ture data can be read at any time through the SMBus port.
Nine SMBus addresses are programmable for the TC1068,
which allows for a multi-sensor configuration. Also, there is
low-power Standby mode where temperature acquisition is
suspended.

Figure 1. Temperature-vs-Setpoint Event Generation

STANDBY MODE

The TC1068 allows the host to put it into a low power

mode (I

= 10

A, max) Standby mode. In this mode, the

A/D converter is halted, and the temperature data registers
are frozen. The SMBus port operates normally. Standby
mode can be enabled with either the STBY# input pin or the
CHIP STOP bit in the CONFIG register. The following table
summarizes this operation.

Temperature

Setpoints

Time

EXT_HLIM

INT_HLIM

EXT_LLIM

INT_LLIM

EXT_TEMP

INT_TEMP

ALERT#

ASSERT
ALERT#

Note: This diagram implies that the appropriate setpoint is moved, temporarily,
after each ALERT# event to suppress re-assertion of ALERT# immediately
after the ARA/de-assertion.

COMP#

TC1068

SMBus Thermal Sensor with
External Diode Input

TC1068-1 2/8/99

Figure 2. TC1068 Functional Description Flowchart

YES

STBY mode

active?

YES

POR, initialize

all registers

YES

Start internal

conversion,

STATUS D[7]

STBY

active?

EOC?

STBY

released?

Thermal Trip?

Start external

conversion

STBY

active?

Ext. diode

open?

EOC?

YES

Update

EXT_TEMP

Thermal Trip?

YES

CONFIG

[D7] active?

YES

Enable

ALERT#

Set appropriate

STATUS bit

D[6:2]

Reset STATUS

bit D[7]

YES

Execute

STATUS read and

clear STATUS

Execute SMBus

read

Execute SMBus

write

STATUS

read?

Read/

Write?

ALERT#

active?

Disable and re-arm

ALERT#, send

local address to host

Address

match?

YES

WRITE

YES

READ

YES

One Shot?

YES

Win

arbitration?

ARA

bus

arbitration

YES

Stop conv., reset

STATUS D[7]

Monitor SMBus

for START

condition

Valid

command?

ARA?

YES

Rest Period

according to

CONV_RATE

register

Rest Period

over?

Performance

conversion cycle

Update

INT_TEMP

One

Shot?

YES

EXT_HLIM

Trip?

Enable COMP#

YES

Disable COMP#

EXT_LLIM

Trip?

YES

SMBus Thermal Sensor with

External Diode Input

TC1068

TC1068-1 2/8/99

Standby Mode Operation

STBY#

Chip Stop Bit

One Shot?

Operating Mode

Don't Care

Standby

Don't Care

Normal

Standby

Yes

Normal

(1 Conversion Only,

then Standby)

SMBus SLAVE ADDRESS

The two pins ADD1 and ADD0 are tri-state input pins

which determine the 7-bit SMBus slave address of the
TC1068. The address is latched during POR. The allowable
addresses are summarized in the following table.

SERIAL PORT OPERATION

The Serial Clock input (SCL) and bi-directional data port

(SDAT) form a 2-wire bi-directional serial port for program-
ming and interrogating the TC1068. The following conven-
tions are used in the bus architecture in the followingtable.

All transfers take place under control of a host, usually

a CPU or microcontroller, acting as the Master, which
provides the clock signal for all transfers. The TC1068
always operates as a slave. The serial protocol is illustrated
in Figure 3. All data transfers have two phases; all bytes are
transferred MSB first. Accesses are initiated by a start
condition (START), followed by a device address byte and
one or more data bytes. The device address byte includes
a Read/Write selection bit. Each access must be terminated
by a Stop Condition (STOP). A convention called

Acknowl-

edge (ACK) confirms receipt of each byte. Note that SDA
can change only during periods when SCL is LOW (SDA
changes while SCL is High are reserved for Start and Stop
conditions.)

TC1068 Serial Bus Conventions

Term

Explanation

Transmitter

The device sending data to the bus.

Receiver

The device receiving data from the bus.

Master

The device which controls the bus: initiating
transfers (START), generating the clock, and
terminating transfers (STOP).

Slave

The device addressed by the master.

Start

A unique condition signaling the beginning of
a transfer indicated by SDA falling (High
Low) while SCL is high.

Stop

A unique condition signaling the end of a
transfer indicated by SDA rising (Low High)
while SCL is high.

ACK

A receiver acknowledges the receipt of each
byte with this unique condition. The receiver
drives SDA low during SCL high of the ACK
clock-pulse. The Master provides the clock
pulse for the ACK cycle.

Busy

Communication is not possible because the
bus is in use.

NOT Busy

When the bus is idle, both SDA and SCL
will remain high.

Data Valid

The state of SDA must remain stable during
the High period of SCL in order for a data bit to
be considered valid. SDA only changes state
while SCL is low during normal data transfers
(see Start and Stop conditions).

Address Decode Table

ADD0

ADD1

SMBus Address

0011 000

open (3-state)

0011 001

0011 010

open (3-state)

0101 001

open (3-state)

0101 010

open (3-state)

0101 011

1001 100

open (3-state)

1001 101

1001 110

Start Condition (START)

The TC1068 continuously monitors the SDA and SCL

lines for a start condition (a High to Low transition of SDA
while SCL is High), and will not respond until this condition
is met.

Address Byte

Immediately following the Start Condition, the host must

transmit the address byte to the TC1068. The states of
ADD1 and ADD0 during power-up determine the 7-bit
SMBus address for the TC1068. The 7-bit address transmit-
ted in the serial bit stream must match for the TC1068 to
respond with an Acknowledge (indicating the TC1068 is on
the bus and ready to accept data). The eighth bit in the
Address Byte is a Read-Write Bit. This bit is 1 for a read
operation or 0 for a write operation.

Acknowledge (ACK)

Acknowledge (ACK) provides a positive handshake

between the host and the TC1068. The host releases SDA
after transmitting eight bits, then generates a ninth clock
cycle to allow the TC1068 to pull the SDA line Low to

TC1068

SMBus Thermal Sensor with
External Diode Input

TC1068-1 2/8/99

Figure 3. SMBus Protocols

ADDRESS

ACK

COMMAND

ACK

DATA

ACK

8 Bits

7 Bits

8 Bits

Slave Address

Command Byte: selects
which register you are
writing to.

Data Byte: data goes
into the register set
by the command byte.

Write Byte Format

Read Byte Format

ADDRESS WR

ACK

COMMAND

ACK

ADDRESS

ACK

DATA

NACK P

7 Bits

8 Bits

7 Bits

8 Bits

Slave Address

Command Byte: selects
which register you are
reading from.

Slave Address: repeated
due to change in data-
flow direction.

Data Byte: reads from
the register set by the
command byte.

Receive Byte Format

ADDRESS

ACK

DATA

NACK P

7 Bits

8 Bits

Data Byte: reads data from
the register commanded by
the last Read Byte.

S = Start Condition

P = Stop Condition

Shaded = Slave Transmission

Send Byte Format

ADDRESS WR

ACK

COMMAND

ACK

7 Bits

8 Bits

Command Byte: sends
command with no data,
usually used for one-shot
command.

SMBus Thermal Sensor with

External Diode Input

TC1068

TC1068-1 2/8/99

A/D Conversion Rate Register (CONV_RATE)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

Reserved

MSB

LSB

Command Byte Description

Command

Code

Function

RIT

00h

Read Internal Temp (INT_TEMP)

RET

01h

Read External Temp (EXT_TEMP)

02h

Read Status Byte (STATUS)

03h

Read Configuration Byte (CONFIG)

RCR

04h

Read Conversion Rate Byte
(CONV_RATE)

RIHL

05h

Read Internal High Limit (INT_HLIM)

RILL

06h

Read Internal Low Limit (INT_LLIM)

REHL

07h

Read External High Limit (EXT_HLIM)

RELL

08h

Read External Low Limit (EXT_LLIM)

09h

Write Configuration Byte (CONFIG)

WCR

0Ah

Write Conversion Rate Byte
(CONV_RATE)

WIHL

0Bh

Write Internal High Limit
(INT_HLIM)

WILL

0Ch

Write Internal Low Limit (INT_LLIM)

WEHL

0Dh

Write External High Limit (EXT_HLIM)

WELL

0Eh

Write External Low Limit (EXT_LLIM)

OSHT

0Fh

One Shot Temp Measurement

RMID

FEh

Read Manufacturer ID (MFR_ID)

RMREV

FFh

Read Manufacturer Revision
Number (MFR_REV)

Configuration Register (Config), 8-Bits, Read/
Write

Configuration Register (Config)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

Mask1 Chip Stop

Reserved

Bit

POR State Function

Operation

D[7]

Interrupt Mask

1 = mask ALERT#/

(see text)

COMP#
0 = don't mask
ALERT #/COMP#

D[6]

Standby switch

1 = standby,
0 = normal

D[5] D[0]

Reserved

N/A

Always returns
zero when read.

A/D Conversion Rate Register
(CONV_RATE), 8-Bits, Read/Write

Bit

POR State Function

Operation

D[7:3]

Reserved Always

N/A

returns zero when
read.

D[2:0]

010b

Conversion rate bits.

See below.

A/D Conversion Rate Selection

Conversion Rate
Sa/sec

0.0625

0.125

0.25

0.5

1.0

2.0

4.0

8.0

NOTE: Conversion rate denotes actual sampling of both internal

and

external sensors.

NOTE: Proper device operation is NOT guaranteed if undefined locations
(10h to FDh) are addressed. In case of erroneous SMBus operation
(RECEIVE_BYTE command issued immediately after WRITE_BYTE com-
mand) the TC1068 will ACKnowledge the address and return 1111 1111b
to signify an error. Under no condition will it implement an SMBus
"timeout."

acknowledge that it successfully received the previous
eight bit of data or address.

Data Byte

After a successful ACK of the address byte, the host

must transmit the data byte to be written or clock out the data
to be read. (See the appropriate timing diagrams.) ACK will
be generated after a successful write of a data byte into the
TC1068.

Stop Condition (STOP)

Communications must be terminated by a stop condi-

tion (a Low to High transition of SDA while SCL is High). The
Stop Condition must be communicated by the transmitter to
the TC1068. (See TCN75 data sheet for serial bus timing
diagrams.)

REGISTER SET AND PROGRAMMER'S MODEL

TC1068 Command Set

The TC1068 supports four SMBus command protocols.

These are READ_BYTE, WRITE_BYTE, SEND_BYTE, and
RECEIVE_BYTE. See System Management Bus Specifica-
tion Rev. 1.0 for details.

TC1068

SMBus Thermal Sensor with
External Diode Input

TC1068-1 2/8/99

Temperature Registers, 8-Bits, Read-Only
(INT_TEMP, EXT_TEMP)

The binary value (2's complement format) in these two

registers represents temperature of the internal and exter-
nal sensors following a conversion cycle. The registers are
automatically updated in an alternating manner.

Internal Temperature Register (INT_TEMP)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

MSB

LSB

External Temperature Register (EXT_TEMP)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

MSB

LSB

Temperature Threshold Setpoint Registers,
8-Bits, Read-Write (INT_HLIM, INT_LLIM,
EXT_HLIM, EXT_LLIM)

These registers store the values of the upper and lower

temperature setpoints for event detection. The value is in
2's-complement binary. INT_HLIM and INT_LLIM are com-
pared with the INT_TEMP value, and EXT_HLIM and
EXT_LLIM are compared with EXT_TEMP. These registers
may be written at any time.

Internal High Limit Setpoint Register (INT_HLIM)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

MSB

LSB

Internal Low Limit Setpoint Register (INT_LLIM)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

MSB

LSB

External High Limit Setpoint Register (EXT_HLIM)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

MSB

LSB

External Low Limit Setpoint Register (EXT_LLIM)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

MSB

LSB

NOTE: POR states:

INT_HLIM

01111111b

+127

INT_LLIM

11001001b

EXT_HLIM

01111111b

+127

EXT_LLIM

11001001b

In the two temperature data and four threshold setpoint

registers, each unit value represents one degree (Celsius).
The value is in 2's-complement binary format such that a
reading of 00000000b corresponds to 0

C. Examples of this

temperature-to-binary value relationship are shown in the
following table.

Temperature-to-Digital Value Conversion

(INT_TEMP, EXT_TEMP, INT_HLIM, INT_LLIM,

EXT_HLIM, EXT_LLIM)

Actual

Rounded

Binary

Hex

Temperature

Value

+130.00

+127

01111111

+127.00

+127

01111111

+126.50

+127

01111111

+25.25

+25

00011001

+0.50

00000001

+0.25

00000000

0.00

00000000

0.25

00000000

0.50

00000000

0.75

11111111

1.00

11111111

25.00

11100111

25.25

11100110

54.75

11001001

55.00

11001001

65.00

10111111

SMBus Thermal Sensor with

External Diode Input

TC1068

TC1068-1 2/8/99

Manufacturer's Identification Register (MFR_ID)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

MSB

LSB

Name

Description

POR

Read Write

State

INT_TEMP

Internal sensor

0000 0000b*

temperature
(2's complement)

EXT_TEMP

External sensor

0000 0000b*

temperature
(2's complement)

STATUS

STATUS register

0000 0000b

CONFIG

CONFIG register

1000 0000b

CONV_RATE A/D conversion

0000 0010b

rate register

INT_HLIM

Internal high

0111 1111b

limit
(2's complement)

INT_LLIM

Internal low

1100 1001b

limit
(2's complement)

EXT_HLIM

External high

0111 1111b

limit
(2's complement)

EXT_LLIM

External low

1100 1001b

limit
(2's complement)

MFR_ID

ASCII for letter "T" 0101 0100b

(Microchip)

MFR_REV

Serial device

revision #

*NOTE: The INT_TEMP and EXT_TEMP register immediately will be

updated by the A/D converter after POR. If STBY# is low at power-
up, INT_TEMP and EXT_TEMP will remain in POR state (0000
0000b).
**MFR_REV will sequence 01h, 02h, 03h, etc. by mask changes.

The TC1068's register set is summarized in the follow-

ing table. All registers are 8-bits wide.

Manufacturer's Identification Register
(MFR_ID), 8-Bits, Read Only:

Manufacturer's Revision Register (MFR_REV)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

MSB

LSB

Manufacturer's Revision Register
(MFR_REV), 8-Bits, Read Only:

Register Set Summary:

Status Register (Status), 8-Bits, Read Only:

Status Register (Status)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

Busy Flag1 Flag2

Flag3 Flag4

Flag5

Flag6 Reserved

Bit(s)

POR

Function

Operation*

State

D[7]

Signal A/D

1 = A/D busy,

converter is busy.

0 = A/D idle

D[6]

Interrupt flag for

1 = interrupt occurred,

INT_HLIM event

0 = none

D[5]

Interrupt flag for

1 = interrupt occurred,

INT_LLIM event

0 = none

D[4]

Interrupt flag for

1 = interrupt occurred,

EXT_HLIM event

0 = none

D[3]

Interrupt flag for

1 = interrupt occurred,

EXT_LLIM event

0 = none

D[2]

External diode

1 = external diode fault

"fault" flag

0 = external diode OK

D[1:0]

Reserved

N/A

Always
returns zero.

NOTE: All status bits are cleared after a read operation is performed on

STATUS. The EXT_TEMP register will read +127

C if an external

diode "open".

SMBus Thermal Sensor with

External Diode Input

TC1068

TC1068-1 2/8/99

Information contained in this publication regarding device applications and the like is intended through suggestion only and may be superseded by
updates. It is your responsibility to ensure that your application meets with your specifications. No representation or warranty is given and no liability is
assumed by Microchip Technology Incorporated with respect to the accuracy or use of such information, or infringement of patents or other intellectual
property rights arising from such use or otherwise. Use of Microchipís products as critical components in life support systems is not authorized except with
express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, except as maybe explicitly expressed herein, under any intellec-
tual property rights. The Microchip logo and name are registered trademarks of Microchip Technology Inc. in the U.S.A. and other countries. All rights
reserved. All other trademarks mentioned herein are the property of their respective companies.

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01/09/01

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ALES

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ERVICE

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