I

2

C Interface

SDA

SCL

Pointer Register

(Selects register for

communication)

Address

Data

Temperature

(Read-Only)

Pointer = 00000000

Product ID

(Read-Only)

Pointer = 00000111

TOS Set Point

(Read-Write)

Pointer = 00000011

Configuration

(Read-Write)

Pointer = 00000001

THYST Set Point

(Read-Write)

Pointer = 00000010

LM75A

www.ti.com

SNOS808P – JANUARY 2000 – REVISED DECEMBER 2014

7.5.8 Internal Register Structure

Figure 8. Register Structure

There are four data registers in the LM75A and an additional Product ID register selected by the Pointer register.

At power-up the Pointer is set to “000”; the location for the Temperature Register. The Pointer register latches

whatever the last location it was set to. In Interrupt Mode, a read from the LM75A, or placing the device in

shutdown mode, resets the O.S. output. All registers are read and write, except the Temperature register and the

LM75A's Product ID register, which are read-only.

A write to the LM75A will always include the address byte and the Pointer byte. A write to the Configuration

register requires one data byte, and the TOS and THYST registers require two data bytes.

Reading the LM75A can take place either of two ways: If the location latched in the Pointer is correct (most of the

time it is expected that the Pointer will point to the Temperature register because it will be the data most

frequently read from the LM75A), then the read can simply consist of an address byte, followed by retrieving the

corresponding number of data bytes. If the Pointer needs to be set, then an address byte, pointer byte, repeat

start, and another address byte will accomplish a read.

The first data byte is the most significant byte with most significant bit first, permitting only as much data as

necessary to be read to determine temperature condition. For instance, if the first four bits of the temperature

data indicates an overtemperature condition, the host processor could immediately take action to remedy the

excessive temperatures. At the end of a read, the LM75A can accept either Acknowledge or No Acknowledge

from the Master (No Acknowledge is typically used as a signal for the slave that the Master has read its last

byte).

7.6 Register Maps

7.6.1 Pointer Register (Selects Which Registers Will Be Read From or Written to):

P7

P6

P5

P4

P3

P2

P1

P0

0

0

0

0

0

Register Select

P0-P1: Register Select:

P2

P1

P0

Register

0

0

0

Temperature (Read-only) (Power-up default)

0

0

1

Configuration (Read/Write)

0

1

0

THYST (Read/Write)

0

1

1

TOS (Read/Write)

1

1

1

Product ID Register

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