Rainbow Electronics LM85 - Manual (Page 17)

Functional Description
(Continued)
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).
Zone 1: External Diode 1 (processor)
Zone 2: Internal Sensor
Zone 3: External Diode 2
TABLE 4. Fan Zone Setting
ZON[2:0] Fan Configuration
000 Fan on zone 1 auto
001 Fan on zone 2 auto
010 Fan on zone 3 auto
011 Fan always on full
100 Fan disabled
101 Fan controlled by hottest of zones 2, 3
110 Fan controlled by hottest of zones 1, 2, 3
111 Fan manually controlled (Test Mode)
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.
TABLE 5. Fan Spin-Up Register
SPIN[2:0] Spin Up Time
000 0 sec
001 100 ms
010 250 ms
011 400 ms
100 700 ms
101 1000 ms
110 2000 ms
111 4000 ms
4.15 Registers 5F-61h: Auto Fan Speed Range, PWM Frequency
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?
5Fh R/W Zone1 Range/Fan1
Frequency
RAN3 RAN2 RAN1 RAN0 RES FRQ2 FRQ1 FRQ0 C4h U
60h R/W Zone2 Range/Fan2
Frequency
RAN3 RAN2 RAN1 RAN0 RES FRQ2 FRQ1 FRQ0 C4h U
61h R/W Zone3 Range/Fan3
Frequency
RAN3 RAN2 RAN1 RAN0 RES FRQ2 FRQ1 FRQ0 C4h U
LM85
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