LM75B_2

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 02 — 9 December 2008

7 of 29

NXP Semiconductors

LM75B

Digital temperature sensor and thermal watchdog

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 5 and Table 6. 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 LM75B 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

read a register that is different from the one that has been recently read, the pointer byte

must be included. However, a write to the LM75B must always include the pointer byte in

the statement. The bus communication protocols are described in Section 7.10.

At power-up, the Pointer value is equal to 00 and the Temp register is selected; users can

then read the Temp data without specifying the pointer byte.

7.4.2 Configuration register

The Configuration register (Conf) is a write/read register and contains an 8-bit

non-complement data byte that is used to configure the device for different operation

conditions. Table 7 shows the bit assignments of this register.

Table 5.

Pointer register

B7

B6

B5

B4

B3

B2

B[1:0]

0

0

0

0

0

0

pointer value

Table 6.

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)

Table 7.

Conf register

Legend: * = default value.

Bit

Symbol

Access Value Description

B[7:5]

reserved

R/W

000*

reserved for manufacturer’s use; should be kept as

zeroes for normal operation

B[4:3]

OS_F_QUE[1:0] R/W

OS fault queue programming

00*

queue value = 1

01

queue value = 2

10

queue value = 4

11

queue value = 6

B2

OS_POL

R/W

OS polarity selection

0*

OS active LOW

1

OS active HIGH