LM85 National Semiconductor, LM85 Datasheet - Page 17

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

Register
Address
5Fh
60h
61h
Functional Description
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.
Bits [7:5] Zone/Mode
Bits [7:5] of the Fan Configuration registers associate each fan with a temperature sensor. When in Auto Fan Mode the fan will
be assigned to a zone, and its PWM duty cycle will be adjusted according to the temperature of that zone. If ‘Hottest’ option is
selected (101 or 110), the fan will be controlled by the hottest of zones 2 and 3, or of zones 1, 2, and 3. When in manual control
mode, the Current PWM duty registers (30h-32h) become Read/Write. It is then possible to control the PWM outputs with
software by writing to these registers. When the fan is disabled (100) the corresponding PWM output should be driven low (or
high, if inverted).
Bit [4] PWM Invert
Bit [4] inverts the PWM output. If set to 0, 100% duty cycle will yield an output that is always high. If set to 1, 100% duty cycle
will yield an output that is always low.
Bit [3] Reserved
Bits [2:0] Spin Up
Bits [2:0] specify the ‘spin up’ time for the fan. When a fan is being started from a stationary state, the PWM output is held at 100%
duty cycle for the time specified in the table below before scaling to a lower speed.
4.15 Registers 5F-61h: Auto Fan Speed Range, PWM Frequency
Zone 1: External Diode 1 (processor)
Zone 2: Internal Sensor
Zone 3: External Diode 2
Read/
Write
R/W
R/W
R/W
Register
Name
Zone1 Range/Fan1
Frequency
Zone2 Range/Fan2
Frequency
Zone3 Range/Fan3
Frequency
ZON[2:0]
000
001
010
011
100
101
110
111
SPIN[2:0]
000
001
010
011
100
101
110
111
(Continued)
Bit 7
(MSB)
RAN3
RAN3
RAN3
TABLE 5. Fan Spin-Up Register
Fan Configuration
Fan on zone 1 auto
Fan on zone 2 auto
Fan on zone 3 auto
Fan always on full
Fan disabled
Fan controlled by hottest of zones 2, 3
Fan controlled by hottest of zones 1, 2, 3
Fan manually controlled (Test Mode)
TABLE 4. Fan Zone Setting
Bit 6
RAN2
RAN2
RAN2
Bit 5
RAN1
RAN1
RAN1
Spin Up Time
0 sec
100 ms
250 ms
400 ms
700 ms
1000 ms
2000 ms
4000 ms
17
Bit 4
RAN0
RAN0
RAN0
Bit 3
RES
RES
RES
Bit 2
FRQ2
FRQ2
FRQ2
Bit 1
FRQ1
FRQ1
FRQ1
Bit 0
(LSB)
FRQ0
FRQ0
FRQ0
Default
Value
C4h
C4h
C4h
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Lock?
U
U
U