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Functional Description (Continued)

13.16 Value RAM—Address 15h–3Fh

Address A6–A0 Description

15h Manufacturers Test Register

19h DAC data register; power on default

7:0

=1111 1111 binary

20h +2.5Vin reading

21h Vccp1 reading

22h +3.3Vin reading

23h +5Vin reading

24h +12Vin reading

25h Vccp2 reading

26h Reserved reading

27h Temperature reading (8 MSBs)

28h FAN1 reading

Note: This location stores the number of counts of the internal clock per revolution.

29h FAN2 reading

Note: This location stores the number of counts of the internal clock per revolution.

2Ah Reserved

2Bh +2.5Vin High Limit

2Ch +2.5Vin Low Limit

2Dh Vccp1 High Limit

2Eh Vccp1 Low Limit

2Fh +3.3Vin High Limit

30h +3.3Vin Low Limit

31h +5Vin High Limit

32h +5Vin Low Limit

33h +12Vin High Limit

34h +12Vin Low Limit

35h Vccp2 High Limit

36h Vccp2 Low Limit

37h T_CRIT Limit (Extended Mode)

38h LOW Limit (Extended Mode)

39h HIGH Temperature Limit

3Ah HIHYST Temperature Limit

3Bh FAN1 Fan Count Limit

Note: It is the number of counts of the internal clock for the Low Limit of the fan speed.

3Ch FAN2 Fan Count Limit

Note: It is the number of counts of the internal clock for the Low Limit of the fan speed.

3Dh Reserved

3Eh Company Identification. The number in this register identifies National Semiconductor (0000 0001)

3Fh Stepping Register LM81 revision number (0000 0011)

Note: Setting all ones to the high limits for voltages and fans (0111 1111 binary for temperature) means interrupts will never be generated except the case when

voltages go below the low limits.

For voltage input high limits, the device is doing a greater than comparison. For low limits, however, it is doing a less than or equal to comparison.

LM81