LM75A_4

© NXP B.V. 2007. All rights reserved.

Product data sheet

Rev. 04 — 10 July 2007

6 of 24

NXP Semiconductors

LM75A

Digital temperature sensor and thermal watchdog

8 devices can be connected to the same bus without address conflict. Because the input

pins, SCL, SDA and A2 to A0, are not internally biased, it is important that they should not

be left floating in any application.

7.4 Register list

The LM75A contains four data registers beside the pointer register as listed in Table 5.

The pointer value, read/write capability and default content at power-up of the registers

are also shown in Table 5.

7.4.1 Pointer register

The Pointer register contains an 8-bit data byte, of which the two LSB bits represent the

pointer value of the other four registers, and the other 6 MSB bits are equal to 0, as shown

in Table 6 and Table 7. The Pointer register is not accessible to the user, but is used to

select the data register for write/read operation by including the pointer data byte in the

bus command.

Because the Pointer value is latched into the Pointer register when the bus command

(which includes the pointer byte) is executed, a read from the LM75A may or may not

include the pointer byte in the statement. To read again a register that has been recently

read and the pointer has been preset, the pointer byte does not have to be included. To

Table 4.

Address table

1 = HIGH; 0 = LOW.

MSB

LSB

1001A2

A1

A0

Table 5.

Register table

Register

name

Pointer

value

R/W

POR

state

Description

Conf

01h

R/W

00h

Configuration register: contains a single 8-bit data

byte; to set the device operating condition; default = 0.

Temp

00h

read only

n/a

Temperature register: contains two 8-bit data bytes;

to store the measured Temp data.

Tos

03h

R/W

5000h

Overtemperature shutdown threshold register:

contains two 8-bit data bytes; to store the

Thyst

02h

R/W

4B00h

Hysteresis register: contains two 8-bit data bytes;

Table 6.

Pointer register

B7

B6

B5

B4

B3

B2

B[1:0]

0

0

0

0

0

0

pointer value

Table 7.

Pointer value

B1

B0

Selected register

0

0

Temperature register (Temp)

0

1

Configuration register (Conf)

1

0

Hysteresis register (Thyst)

1

1

Overtemperature shutdown register (Tos)