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© Andigilog, Inc. 2006
www.andigilog.com
October 2006 - 70A06010
aSC7621
Fan Register Device Set-Up
The BIOS will follow the following steps to configure the fan registers on the aSC7621. The registers corresponding to each
function are listed. All steps may not be necessary if default values are acceptable. Regardless of all changes made by the
BIOS to the fan limit and parameter registers during configuration, the aSC7621 will continue to operate based on default
values until the START bit (bit 0), in the Ready/Lock/Start/Override register (address 40h), is set. Once the fan mode is
updated, by setting the START bit to 1, the aSC7621 will operate using the values that were set by the BIOS in the fan
control limit and parameter registers (address in the range 3Ch through 75h). It is assumed that each Temperature Zone has
already been configured to be associated with the appropriate temperature measurement either with the default settings or to
the user’s preference. See previous section on Temperature Zone configuration.
1.
Set limits and parameters (not necessarily in this order):
•
[3Ch, 5F-61h] Set PWM frequency for the fan and auto fan control range for each zone.
•
[3Ch, 62-63h] Set spike smoothing and min/off.
•
[5C-5Eh] Set the fan spin-up delay.
•
[75h] Set PWM spin-up mode to terminate after time set in [5C-5Eh]. Value = 00h instead of default 01h.
•
[5C-5Eh] Match fan with a corresponding thermal zone.
•
[3Bh, 67-69h] Set the fan temperature limits.
•
[3Dh, 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.
[40h] (Optional) Set bit 1 (LOCK) to lock the fan limit and parameter registers. WARNING: this is a non-reversible
change in state and locks out further change in critical fan control parameters until power is removed from the aSC7621.
Register 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
Zone 1 Range
Fan1 Frequency
RAN3
RAN2
RAN1
RAN0
HLFRQ
FRQ2
FRQ1
FRQ0
C3
X
60h
R/W
Zone 2 Range/
Fan 2 Frequency
RAN3
RAN2
RAN1
RAN0
HLFRQ
FRQ2
FRQ1
FRQ0
C3
X
61h
R/W
Zone 3 Range/
Fan 3 Frequency
RAN3
RAN2
RAN1
RAN0
HLFRQ
FRQ2
FRQ1
FRQ0
C3
X
3Ch
R/W
Zone 4 Range,
Spike Smoothing
RAN3
RAN2
RAN1
RAN0
ZN4E
ZN4-2
ZN4-1
ZN4-0
C3h
X
In Auto Fan Mode, when the temperature for a zone is above the Temperature Limit (Registers 3Bh, 67-69h) and below its
Absolute Temperature Limit (Registers 3Dh 6A-6Ch), the speed of a fan assigned to that zone is determined as follows:
When the temperature reaches the Fan Temp Limit for a zone, the PWM output assigned to that zone will be Fan PWM
Minimum. Between Fan Temp Limit and (Fan Temp Limit + Range), the PWM duty cycle will increase linearly according to
the temperature as shown in the figure below. The PWM duty cycle will be 100% at (Fan Temp Limit + Range).
PWM frequency - FRQ[3:0] and HLFRQ
The PWM frequency bits [3:0] determine the PWM frequency for the fan. The aSC7621 has high and low frequency ranges
for the PWM outputs that are controlled by the HLFRQ bit.
PWM Frequency Selection (Default = 0011 ≈ 30 Hz).
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