TABLE 3. Temperature Limits vs Register Settings

Temperature

Reading (Decimal)

Reading (Hex)

−127˚C

−127

81h

.

.

.

.

.

.

.

.

.

−50˚C

−50

CEh

.

.

.

.

.

.

.

.

.

0˚C

0

00h

.

.

.

.

.

.

.

.

.

50˚C

50

32h

.

.

.

.

.

.

.

.

.

127˚C

127

7Fh

4.13 Registers 54-5Bh: Fan Tachometer Low Limit

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

54h

55h

R/W

R/W

Tach1 Minimum LSB

Tach1 Minimum MSB

7

15

6

14

5

13

4

12

3

11

2

10

1

9

0

8

FFh

FFh

56h

57h

R/W

R/W

Tach2 Minimum LSB

Tach2 Minimum MSB

7

15

6

14

5

13

4

12

3

11

2

10

1

9

0

8

FFh

FFh

58h

59h

R/W

R/W

Tach3 Minimum LSB

Tach3 Minimum MSB

7

15

6

14

5

13

4

12

3

11

2

10

1

9

0

8

FFh

FFh

5Ah

5Bh

R/W

R/W

Tach4 Minimum LSB

Tach4 Minimum MSB

7

15

6

14

5

13

4

12

3

11

2

10

1

9

0

8

FFh

FFh

The Fan Tachometer Low Limit registers indicate the tachometer reading under which the corresponding bit will be set in the

Interrupt Status Register 2 register. In Auto Fan Control mode, the fan can run at low speeds, so care should be taken in software

to ensure that the limit is high enough not to cause sporadic alerts. The fan tachometer will not cause a bit to be set in Interrupt

Status Register 2 if the current value in Current PWM Duty registers is 00h or if the fan 1 disabled via the Fan Configuration

Register. Interrupts will never be generated for a fan if its minimum is set to FF FFh.

Given the insignificance of Bit 0 and Bit 1, these bits could be programmed to remember which fan is which, as follows.

Fan

Bit 1

Bit 0

CPU

0

0

Memory

0

1

Chassis Front

1

0

Chassis Rear

1

1

Setting the Ready/Lock/Start/Override register Lock bit has no effect these registers.

4.14 Registers 5C-5Eh: Fan Configuration

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?

5Ch

R/W

Fan1 Configuration

ZON2

ZON1

ZON0

INV

RES

SPIN2

SPIN1

SPIN0

62h

U

5Dh

R/W

Fan2 Configuration

ZON2

ZON1

ZON0

INV

RES

SPIN2

SPIN1

SPIN0

62h

U

5Eh

R/W

Fan3 Configuration

ZON2

ZON1

ZON0

INV

RES

SPIN2

SPIN1

SPIN0

62h

U

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