Functional Description (Continued)
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
16h
17h
0000 0000
0000 0000
0100 0110
Channel Mode Register
Internal Temp. Hardware
High Limit
70 ˚C Default - User adjustable.
85 ˚C Default - User adjustable.
Defaults to full scale DAC setting.
External Temp. Hardware
High Limit
18h
19h
0101 0101
1111 1111
Value RAM DAC Data
Register
Value RAM
1Ah-3Fh
(See Section 13.18) Contains: monitoring results
(temperature, voltages, fan counts), WATCHDOG
limits, and Company/Stepping IDs
Company ID
Revision
3Eh
3Fh
0000 0010
0000 0110
This designates the National Semiconductor LM87.
Revisions of this device will start with 1 and increment
by one.
Configuration Register 1
Interrupt Status Register 1
Interrupt Status Register 2
Interrupt Mask Register 1
Interrupt Mask Register 2
CI Clear Register
40h
41h
42h
43h
44h
46h
47h
0000 1000
0000 0000
0000 0000
0000 0000
0000 0000
0000 0000
0101 XXXX
VID0-3/Fan Divisor Register
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
4Ah
4Ch
1000 000X
0000 0000
0000 0000
The lower bit reflects the state of VID4 input.
Configuration Register 2
Interrupt Status Register 1
Mirror
Interrupt Status Register 2
Mirror
4Dh
80h
0000 0000
0010 0000
SMBALERT# Enable
11
www.national.com
NSC [ National Semiconductor ]
