2.1 Internal Registers of the LM87

TABLE 1. The internal registers and their corresponding internal LM87 addresses are as follows:

Register

LM87 Internal Hex

Address

Power on

Value

Notes

Internal Temp. Hardware

High Limit

13h

0100 0110

70 ˚C Default - User adjustable. Lockable by setting bit

1 of register 4Ah.

External Temp. Hardware

High Limit

14h

0101 0101

85 ˚C Default - User adjustable. Lockable by setting bit

2 of register 4Ah.

Test Register

15h

0000 0000

Channel Mode Register

16h

0000 0000

Internal Temp. Hardware

High Limit

17h

0100 0110

70 ˚C Default - User adjustable.

External Temp. Hardware

High Limit

18h

0101 0101

85 ˚C Default - User adjustable.

Value RAM DAC Data

Register

19h

1111 1111

Defaults to full scale DAC setting.

Value RAM

1Ah-3Fh

(See Section 13.18) Contains: monitoring results

(temperature, voltages, fan counts), WATCHDOG

limits, and Company/Stepping IDs

Company ID

3Eh

0000 0010

This designates the National Semiconductor LM87.

Revision

3Fh

0000 0110

Revisions of this device will start with 1 and increment

by one.

Configuration Register 1

40h

0000 1000

Interrupt Status Register 1

41h

0000 0000

Interrupt Status Register 2

42h

0000 0000

Interrupt Mask Register 1

43h

0000 0000

Interrupt Mask Register 2

44h

0000 0000

CI Clear Register

46h

0000 0000

VID0-3/Fan Divisor Register

47h

0101 XXXX

The upper four bits set the divisor for Fan Counters 1

and 2. The lower four bits reflect the state of the

VID0-VID3 inputs.

VID4 Register

49h

1000 000X

The lower bit reflects the state of VID4 input.

Configuration Register 2

4Ah

0000 0000

Interrupt Status Register 1

Mirror

4Ch

0000 0000

Interrupt Status Register 2

Mirror

4Dh

0000 0000

SMBALERT# Enable

80h

0010 0000

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