Functional Description (Continued)
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
CCP
Low Limit 7 6 5 4 3 2 1 0 00h
47h R/W V
CCP
High Limit 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
LM85
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