LM64 datasheet(12/29 Pages) NSC

12 / 29 page

1.0 Functional Description (Continued)

1.5 TEMPERATURE DATA FORMAT

Temperature data can only be read from the Local and

Remote Temperature registers. The High, Low and T_CRIT

setpoint registers are Read/Write.

Remote temperature data is represented by an 11-bit, two’s

complement word with a Least Significant Bit (LSB) equal to

0.125˚C. The data format is a left justified 16-bit word avail-

able in two 8-bit registers. Some examples of temperature

conversions are shown below.

Actual vs. LM64 Remote Temperature Conversion

Actual Remote Diode

Temperature,˚C

LM64 Remote Diode

Temperature Register, ˚C

Binary Results in LM64

Remote Temperature Register

Hex Remote

Temperature

120

+104

0110 1000 0000 0000

6800h

125

+109

0110 1101 0000 0000

6D00h

126

+110

0110 1110 0000 0000

6E00h

130

+114

0111 0010 0010 0000

7200h

135

+119

0111 0111 0000 0000

7700h

140

+124

0111 1100 0000 0000

7C00h

Output is 11-bit two’s complement word. LSB = 0.125 ˚C.

Actual vs. Remote T_Crit Setpoint Example

Actual Remote Diode

T_Crit Setpoint,˚C

Remote T_CRIT

High Setpoint, ˚C

Binary Remote T_CRIT

High Setpoint Value

Hex Remote T_CRIT

High Setpoint Value

126

+110

0110 1110

6Eh

Local Temperature data is represented by an 8-bit, two’s

complement byte with an LSB equal to 1˚C:

Temperature

Digital Output

Binary

Hex

+125˚C

0111 1101

+25˚C

0001 1001

+1˚C

0000 0001

0˚C

0000 0000

−1˚C

1111 1111

−25˚C

1110 0111

−55˚C

1100 1001

1.6 OPEN-DRAIN OUTPUTS, INPUTS, AND PULL-UP

RESISTORS

The SMBDAT, ALERT, T_Crit, GPIO and PWM open-drain

outputs and the GPD, TACH, and A0 inputs are pulled-up by

pull-up resistors to V

DDas suggested in the table below.

Pin Name

Pin Number

Suggested Pull-up Resistor

Range

Typical

SMBCLK

1 k

Ω to2kΩ

1.5 k

Ω

SMBDAT

1 k

Ω to2kΩ

1.5 k

Ω

ALERT

1 k

Ω to5kΩ

Ω

T_Crit

1 k

Ω to5kΩ

Ω

5 k

Ω to 20 kΩ

10 k

Ω

GPIOx

1-3;18,19

5 k

Ω to 20 kΩ

10 k

Ω

GPDx

20-24

5 k

Ω to 20 kΩ

10 k

Ω

PWM

(Note 14)

TACH

1 k

Ω to5kΩ

Ω

Note 14: Depends on the fan drive circuitry connected to this pin. In the

absence of fan control circuitry usea1k

Ω pull-up resistor to VDD.

1.7 DIODE FAULT DETECTION

The LM64 can detect fault conditions caused by the remote

diode. If the D+ pin is detected to be shorted to V

DD, or open:

(1) the Remote Temperature High Byte (RTHB) register is

loaded with 127˚C, (2) the Remote Temperature Low Byte

(RTLB) register is loaded with 0, and (3) the OPEN bit (D2)

in the status register is set. Therefore, if the Remote T_CRIT

setpoint register (RCS): (1) is set to a value less than +127˚C

and (2) the ALERT Mask is disabled, then the ALERT output

pin will be pulled low. If the Remote High Setpoint High Byte

(RHSHB) is set to a value less than +127˚C and (2) the

ALERT Mask is disabled, then the ALERT and T_Crit out-

puts will be pulled low. The OPEN bit by itself will not trigger

an ALERT.

If the D+ pin is shorted to either ground or D−, then the

Remote Temperature High Byte (RTHB) register is loaded

with −128˚C (1000 0000) and the OPEN bit in the ALERT

Status Register will not be set. A temperature reading of

−128˚C indicates that D+ is shorted to either ground or D-. If

the value in the Remote Low Setpoint High Byte (RLSHB)

abled, ALERT will be pulled low.

1.8 COMMUNICATING WITH THE LM64

Each data register in the LM64 falls into one of four types of

user accessibility:

Read Only

Write Only

Read/Write same address

Read/Write different address

A Write to the LM64 is comprised of an address byte and a

command byte. A write to any register requires one data

byte.

Reading the LM64 Registers can take place after the requi-

site register setup sequence takes place. See Section 2.1.1

LM64 Required Initial Fan Control Register Sequence.

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