Datasheet

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
1001A2A1A0
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
overtemperature shutdown T
os
limit; default = 80 °C.
Thyst 02h R/W 4B00h Hysteresis register: contains two 8-bit data bytes;
to store the hysteresis T
hyst
limit; default = 75 °C.
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)