6.3.3 SMBus Interface

Since the LM64 operates as a slave on the SMBus, the SMBCLK line is an input and the SMBDAT line is

bi-directional. The LM64 never drives the SMBCLK line and it does not support clock stretching. The LM64 has

two hardware-selectable 7-bit slave addresses. The user may input a logical High or Low on the A0 Address pin

to select one of the two pre-programmed SMBus slave addresses. The options are as follows:

A0

Pin

SMBus

Address

0x[Hex]

SMBus Slave Address Bits

A6

A5

A4

A3

A2

A1

A0

0

18

0

0

1

1

0

0

0

1

4E

1

0

0

1

1

1

0

6.3.4 Power-On Reset (POR) Default States

For information on the POR default states see Section 7.1.2.

6.3.5 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 available in two 8-bit registers. Some examples of

temperature conversions are shown below.

Table 6-1. Actual vs. LM64 Remote Temperature Conversion(1)

Actual Remote Diode

Temperature,°C

LM64 Remote Diode Temperature

Register, °C

Binary Results in LM64 Remote

Temperature Register

Hex Remote

Temperature Register

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

(1)

Output is 11-bit two's complement word. LSB = 0.125 °C.

Table 6-2. 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

7D

+25°C

0001 1001

19

+1°C

0000 0001

01

0°C

0000 0000

00

−1°C

1111 1111

FF

−25°C

1110 0111

E7

−55°C

1100 1001

C9

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SNAS207B – MAY 2004 – REVISED JANUARY 2024

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