1.

Set limits and parameters (not necessarily in this order):

– [5F-61h] Set PWM frequencies and auto fan control range.

– [62-63h] Set spike smoothing and min/off.

– [5C-5Eh] Set the fan spin-up delays.

– [5C-5Eh] Match each fan with a corresponding thermal zone.

– [67-69h] Set the fan temperature limits.

– [6A-6Ch] Set the temperature absolute limits.

– [64-66h] Set the PWM minimum duty cycle.

– [6D-6Eh] Set the temperature Hysteresis values.

2.

[40h] Set bit 0 (START) to update fan control and limit register values and start fan control based on these new values.

3.

[40h] Set bit 1 (LOCK) to lock the fan limit and parameter registers (optional).

3.0 AUTO FAN CONTROL OPERATING MODE

The LM85 includes the circuitry for automatic fan control. In Auto Fan Mode, the LM85 will automatically adjust the PWM duty

cycle of the PWM outputs. PWM outputs are assigned to a thermal zone based on the fan configuration registers. It is possible

to have more than one PWM output assigned to a thermal zone. For example, PWM outputs 2 and 3, connected to two chassis

fans, may both be controlled by thermal zone 2. At any time, the temperature of a zone exceeds its absolute limit, all PWM outputs

will go to 100% duty cycle to provide maximum cooling to the system.

4.0 REGISTER SET

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?

20h

R

2.5V

7

6

5

4

3

2

1

0

N/A

21h

R

V

CCP

7

6

5

4

3

2

1

0

N/A

22h

R

3.3V

7

6

5

4

3

2

1

0

N/A

23h

R

5V

7

6

5

4

3

2

1

0

N/A

24h

R

12V

7

6

5

4

3

2

1

0

N/A

25h

R

Processor (Zone1) Temp

7

6

5

4

3

2

1

0

N/A

26h

R

Internal (Zone2) Temp

7

6

5

4

3

2

1

0

N/A

27h

R

Remote (Zone3) Temp

7

6

5

4

3

2

1

0

N/A

28h

R

Tach1 LSB

7

6

5

4

3

2

LEVEL1 LEVEL0

N/A

29h

R

Tach1 MSB

15

14

13

12

11

10

9

8

N/A

2Ah

R

Tach2 LSB

7

6

5

4

3

2

LEVEL1 LEVEL0

N/A

2Bh

R

Tach2 MSB

15

14

13

12

11

10

9

8

N/A

2Ch

R

Tach3 LSB

7

6

5

4

3

2

LEVEL1 LEVEL0

N/A

2Dh

R

Tach3 MSB

15

14

13

12

11

10

9

8

N/A

2Eh

R

Tach4 LSB

7

6

5

4

3

2

LEVEL1 LEVEL0

N/A

2Fh

R

Tach4 MSB

15

14

13

12

11

10

9

8

N/A

30h

R/W

Fan1 Current PWM Duty

7

6

5

4

3

2

1

0

N/A

31h

R/W

Fan2 Current PWM Duty

7

6

5

4

3

2

1

0

N/A

32h

R/W

Fan3 Current PWM Duty

7

6

5

4

3

2

1

0

N/A

3Eh

R

Company ID

7

6

5

4

3

2

1

0

01h

3Fh

R

Version/Stepping

VER3 VER2 VER1 VER0

STP3

STP2

STP1

STP0

60h

40h

R/W

Ready/Lock/Start/Override

RES

RES

RES

RES

OVRID READY

LOCK

START

00h

41h

R

Interrupt Status Register 1

ERR

ZN3

ZN2

ZN1

5V

3.3V

V

CCP

2.5V

00h

42h

R

Interrupt Status Register 2 ERR2 ERR1 FAN4 FAN3

FAN2

FAN1

RES

12V

00h

43h

R

VID0–4

RES

RES

RES

VID4

VID3

VID2

VID1

VID0

N/A

44h

R/W

2.5V Low Limit

7

6

5

4

3

2

1

0

00h

45h

R/W

2.5V High Limit

7

6

5

4

3

2

1

0

FFh

46h

R/W

V

7

6

5

4

3

2

1

0

00h

47h

R/W

V

7

6

5

4

3

2

1

0

FFh

48h

R/W

3.3V Low Limit

7

6

5

4

3

2

1

0

00h

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