Register

Address

Read/

Write

Register

Name

Bit 7

(MSB)

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

(LSB)

Default

Value

Lock?

6Fh

R/W

XOR Test Tree Enable

RES

RES

RES

RES

RES

RES

RES

XEN

00h

U

74h

R/W

Tach Monitor Mode

RES

RES T3/4-1 T3/4-0

T2-1

T2-0

T1-1

T1-0

00h

75h

R/W

Fan Spin-up Mode

RES

RES

RES

RES

RES

PWM3

SU

PWM2

SU

PWM1

SU

7h

U

Note: Reserved bits will always return 0 when read.

4.1 Register 20-24h: Voltage Reading

Register

Address

Read/

Write

Register

Name

Bit 7

(MSB)

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

(LSB)

Default

Value

20h

R

2.5V

7

6543210

N/A

21h

R

V

CCP

7

6543210

N/A

22h

R

3.3V

7

6543210

N/A

23h

R

5V

7

6543210

N/A

24h

R

12V

7

6543210

N/A

The Voltage Reading registers are updated automatically by the LM85 at a minimum frequency of 4 Hz. These registers are read

only — a write to these registers has no effect.

4.2 Register 25-27h: Temperature Reading

Register

Address

Read/

Write

Register

Name

Bit 7

(MSB)

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

(LSB)

Default

Value

25h

R

Processor (Zone1) Temp

7

6543210

N/A

26h

R

Internal (Zone2) Temp

7

6543210

N/A

27h

R

Remote (Zone3) Temp

7

6543210

N/A

The Temperature Reading registers reflect the current temperatures of the internal and remote diodes. Processor (Zone1) Temp

register reports the temperature measured by the thermal diode connected to the Remote1− and Remote1+ pins, Remote

(Zone3) Temp register reports the temperature measured by the thermal diode connected to the the Remote2− and Remote2+

pins, and the Internal (Zone2) Temp register reports the temperature measured by the internal (junction) temperature sensor.

Temperatures are represented as 8 bit, 2’s complement, signed numbers, in Celsius, as shown below in Table 1. The Temperature

Reading register will return a value of 80h if the remote diode pins are not used by the board designer or are not functioning

properly. This reading will cause the zone limit bit(s) (bits 6 and 4) in the Interrupt Status Register (41h) and the remote diode fault

status bit(s) (bit 6 or 7) in the Interrupt Status Register 2 (42h) to be set. The Temperature Reading registers are updated

automatically by the LM85 at a minimum frequency of 4 Hz. These registers are read only — a write to these registers has no

effect.

TABLE 1. Temperature vs Register Reading

Temperature

Reading (Dec)

Reading (Hex)

−127˚C

−127

81h

.

.

.

.

.

.

.

.

.

−50˚C

−50

CEh

.

.

.

.

.

.

.

.

.

0˚C

0

00h

.

.

.

.

.

.

.

.

.

127˚C

127

7Fh

www.national.com

10