0 auto fan control operating mode, 0 register set, Functional description – Rainbow Electronics LM85 User Manual
Page 8
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
www.national.com
8