Datasheet

Product data sheet Rev. 6.1 — 6 February 2015 8 of 37

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 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 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. However, the first

temperature reading will be incorrect and must be ignored. Subsequent reads of the

temperature register will be correct.

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 8

shows the bit assignments of this register.

Table 6. Pointer register

B7 B6 B5 B4 B3 B2 B[1:0]

000000pointer 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)

Table 8. 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