TMP401

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SBOS371B – AUGUST 2006 – REVISED OCTOBER 2014

7.6.1 Pointer Register

Figure 16 illustrates the internal register structure of the TMP401. The 8-bit pointer register is used to address a

given data register. The pointer register identifies which of the data registers respond to a read or write command

on the two-wire bus. This register is set with every write command. A write command must be issued to set the

proper value in the pointer register before executing a read command. Table 3 describes the pointer address of

the registers available in the TMP401. The power-on reset (POR) value of the pointer register is 00h (0000

0000b).

7.6.2 Temperature Registers

The TMP401 has four 8-bit registers that hold temperature measurement results. Both the local channel and the

remote channel have a high byte register that contains the most significant bits (MSBs) of the temperature ADC

result and a low byte register that contains the least significant bits (LSBs) of the temperature ADC result. The

local channel high byte address is 00h; the local channel low byte address is 15h. The remote channel high byte

is at address 01h; the remote channel low byte address is 10h. These registers are read-only and are updated by

the ADC each time a temperature measurement is completed.

The TMP401 contains circuitry to assure that a low byte register read command returns data from the same ADC

conversion as the immediately preceding high byte read command. This assurance remains valid only until

another register is read. For proper operation, the high byte of a temperature register must be read first. Read

the low byte register in the next read command. The low byte register may be left unread if the LSBs are not

needed. Alternatively, the temperature registers can be read as a 16-bit register by using a single two-byte read

command from address 00h for the local channel result or from address 01h for the remote channel result. The

high byte is output first, followed by the low byte. Both bytes of this read operation are from the same ADC

conversion. The power-on reset value of both temperature registers is 00h.

7.6.3 Limit Registers

The TMP401 has 11 registers for setting comparator limits for both the local and remote measurement channels.

These registers have read and write capability. The high and low limit registers for both channels span two

registers, as do the temperature registers. The local temperature high limit is set by writing the high byte to

pointer address 0Bh and writing the low byte to pointer address 16h, or by using a single two-byte write

command (high byte first) to pointer address 0Bh. The local temperature high limit is obtained by reading the

high byte from pointer address 05h and the low byte from pointer address 16h, or by using a two-byte read

command from pointer address 05h. The power-on reset value of the local temperature high limit is 55h,

standard, and 00h, extended (+85°C in standard temperature mode; +21°C in extended temperature mode).

Similarly, the local temperature low limit is set by writing the high byte to pointer address 0Ch and writing the low

byte to pointer address 17h, or by using a single two-byte write command to pointer address 0Ch. The local

temperature low limit is read by reading the high byte from pointer address 06h and the low byte from pointer

address 17h, or by using a two-byte read from pointer address 06h. The power-on reset value of the local

temperature low limit register is 00h, standard and extended (0°C in standard temperature mode; –64°C in

extended mode).

The remote temperature high limit is set by writing the high byte to pointer address 0Dh and writing the low byte

to pointer address 13h, or by using a two-byte write command to pointer address 0Dh. The remote temperature

high limit is obtained by reading the high byte from pointer address 07h and the low byte from pointer address

13h, or by using a two-byte read command from pointer address 07h. The power-on reset value of the remote

temperature high limit register is 55h, standard, and 00h, extended (+85°C in standard temperature mode; +21°C

in extended temperature mode).

The remote temperature low limit is set by writing the high byte to pointer address 0Eh and writing the low byte to

pointer address 14h, or by using a two-byte write to pointer address 0Eh. The remote temperature low limit is

read by reading the high byte from pointer address 08h and the low byte from pointer address 14h, or by using a

two-byte read from pointer address 08h. The power-on reset value of the remote temperature low limit register is

00h, standard and extended (0°C in standard temperature mode; –64°C in extended mode).

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