STDS75 datasheet(18/37 Pages) STMICROELECTRONICS

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Functional description

STDS75

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3.1.3

Temperature register

The temperature register is a two-byte (16-bit) “Read only” register (see Table 8 on

page 18). Digital temperatures from the ADC are stored in the temperature register in two’s

complement format, and the contents of this register are updated each time the A/D

conversion is finished.

The user can read data from the temperature register at any time. When a T-to-D conversion

is completed, the new data is loaded into a comparator buffer to evaluate fault conditions

and will update the temperature register if a read cycle is not ongoing. If a READ is ongoing,

the previous temperature will be read. Accessing the STDS75 continuously without waiting

at least one conversion time between communications will prevent the device from updating

the temperature register with a new temperature conversion result. Consequently, the

STDS75 should not be accessed continuously with a wait time of less than tCONV (max).

Depending on the A/D conversion resolution, the 9-, 10-, 11- or 12-bit MSBs of the register

will contain temperature data. All unused bits following the digital temperature will be zero.

The MSB (Bit 15) of the Temperature Register denotes whether the temperature data is

positive or negative. A '0' in Bit 15 is positive and a '1' is negative.

Note:

These are comparable formats to the DS75 and LM75.

3.1.4

Over-limit temperature register (TOS)

The TOS register is a two-byte (16-bit) READ/WRITE register that stores the user-

programmable upper trip-point temperature for the thermal alarm in two’s complement

format (see Table 9 on page 19). This register defaults to 80°C at power-up (i.e., 0101 0000

0000 0000).

The format of the TOS register is identical to that of the temperature register. The 4 LSBs of

the TOS register are hardwired to zero, so data written to these register bits will be ignored.

The MSB position contains the sign bit for the digital temperature and Bit14 contains the

temperature MSB.

The resolution setting for the A/D conversion determines how many bits of the TOS register

are used by the thermal alarm. For example, for 9-bit conversions, the trip-point temperature

is defined by the 9 MSBs of the TOS register, and all remaining bits are “Don’t cares.”

Table 8.

Temperature register format

Bytes

MS byte

LS byte

Bits

MSB

THSB

TLSB

LSB

STDS75

TMSB TD

TD TD TD

9-bit

LSB

10-bit

LSB

11-bit

LSB

12-bit

LSB

Keys:

SB = two’s complement sign bit

TMSB = temperature MSB

TLSB = temperature LSB

TD = temperature data

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