LM85 National Semiconductor, LM85 Datasheet - Page 21

• Manufacturer Part Number: LM85
• Description: Hardware Monitor with Integrated Fan Control
• Manufacturer: National Semiconductor

Register
Address
67h
68h
69h
Functional Description
4.18 Registers 67-69h: Temperature Limit
These are the temperature limits for the individual zones. When the current temperature equals this limit, the fan will be turned
on if it is not already. When the temperature exceeds this limit, the fan speed will be increased according to the algorithm set forth
in the Auto Fan Range, PWM Frequency register description. Default = 90˚C = 5Ah
This register becomes Read Only when the Ready/Lock/Start/Override register Lock bit is set. Any further attempts to write to this
register shall have no effect. After power up the default value is used whenever the Ready/Lock/Start/Override register Start bit
is cleared even though modifications to this register are possible.
Read/
Write
R/W
R/W
R/W
Register
Name
Zone1 Fan Temp Limit
Zone2 Fan Temp Limit
Zone3 Fan Temp Limit
Temperature
Current Duty
TABLE 10. Temperature Limit vs Register Setting
−127˚C
0.3922%
25.098%
50.196%
−50˚C
127˚C
50˚C
0˚C
(Continued)
100%
TABLE 9. PWM Duty vs Register Setting
0%
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Bit 7
(MSB)
7
7
7
Reading (Decimal)
Bit 6
6
6
6
Value (Decimal)
−127
−50
127
50
0
.
.
.
.
.
.
.
.
.
.
.
.
128
255
Bit 5
5
5
5
64
21
0
1
.
.
.
.
.
.
.
.
.
Bit 4
4
4
4
Reading (Hex)
Value (Hex)
Bit 3
3
3
3
CEh
7Fh
81h
00h
32h
FFh
00h
01h
40h
80h
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Bit 2
2
2
2
Bit 1
1
1
1
Bit 0
(LSB)
0
0
0
Default
Value
5Ah
5Ah
5Ah
www.national.com
Lock?
U
U
U