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FM75M8X

Low-Voltage Two-Wire Digital Temperature Sensor with Thermal Alarm

Fairchild Semiconductor 

Over-Limit Signal Temperature Register (TOS)

The TOS register is a two-byte (16-bit) read/write register

that stores the user-programmable upper trip-point tem-

perature for the thermal alarm in two’s-complement for-

mat. At power-up, this register defaults to 80°C (i.e. 0101

0000 0000 0000).

The format of the TOS register is identical to that of the

temperature register (see Figure 9). The four LSBs of the

TOS register are hardwired to zero, so data written to

these register bits is ignored. The MSB position of the

TOS register contains the sign bit for the digital tempera-

ture and bit 14 contains the temperature MSB.

The resolution setting for the T-to-D conversion deter-

mines 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 nine MSBs of the

TOS register and all remaining bits are ignored.

Hysteresis Temperature Register (THYST)

The THYST register is a two-byte (16-bit) read/write regis-

ter that stores the programmable lower trip-point temper-

ature for the thermal alarm in two’s-complement format.

At power-up, this register defaults to 75°C (i.e. 0100

1011 0000 0000).

The THYST register is illustrated in Figure 9. The format

of this register is the same as that of the temperature

register. The four LSBs of the THYST register are hard-

wired to zero, so data written to these bits is ignored.

The resolution setting for the T-to-D conversion deter-

mines how many bits of the THYST register are used by

the thermal alarm. For example, for 9-bit conversions,

the hysteresis temperature is defined by the nine MSBs

of the THYST register and all remaining bits are ignored.

.

MSB 14 13 12 11 10 9 8

SB TMSB T T T T T T

7 6 5 4 3 2 1 LSB

0 9-bit 10-bit 11-bit 12-bit

LSB LSB LSB LSB

0

0

0

SB = Two’s complement sign bit

TMSB = Temperature MSB

T = Temperature data

9-bit LSB = Temperature LSB for 9-bit conversions

10-bit LSB = Temperature LSB for 10-bit conversions

11-bit LSB = Temperature LSB for 11-bit conversions

12-bit LSB = Temperature LSB for 12-bit conversions

Figure 9. THYST Register and TOS Register Format

© 2006 Fairchild Semiconductor Corporation

FM75 Rev. 1.0.8

10

www.fairchildsemi.com

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