
- 24 -
Andigilog, Inc. 2006
www.andigilog.com
August 2006 - 70A05003
aSC7512
Register 54-55h: Fan Tachometer Minimum Limits
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
54h
55h
R/W
Tach Minimum LSB
Tach Minimum MSB
7
15
6
14
5
13
4
12
3
11
2
10
1
9
0
8
FF
FF
The Fan Tachometer Low Limit registers indicate the tachometer reading under which the corresponding bit will be set in the
Interrupt Status Register 2 register. In Auto Fan Control mode, the fan can run at low speeds, so care should be taken in
software to ensure that the limit is high enough not to cause sporadic alerts. The fan tachometer will not cause a bit to be
set in Interrupt Status Register 2 if the current value in Current PWM Duty registers is 00h or if the fan 1 disabled via the Fan
Configuration Register. Interrupts will never be generated for a fan if its minimum is set to FF FFh.
Given the relative insignificance of Bit 0 and Bit 1 of Tach Minimum LSB, these bits could be programmed to designate the
physical location of the fan generating the tachometer signal, as follows:
Register Name
Bit 1
Bit 0
(LSB)
CPU Cooler
0
0
Memory Controller
0
1
Chassis Front
Chassis Rear
1
1
0
1
Table 14 Fan Location
Setting the Ready/Lock/Start/Override register Lock bit has no effect on these registers.
Register 5Ch: Fan Thermal Zone Assignment and Spin-up Mode
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
5Ch
R/W
Fan Configuration
ZON2
ZON1
ZON0
INV
RES
SPIN2
SPIN1
SPIN0
62
X
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 (110), the fan will be controlled by the the hotter of zones 1, or 2. To determine the “hotter zone”, the
PWM level for each zone is calculated then the zone with the higher PWM value (not temperature) is selected. When in
manual control mode, the Current PWM duty register (30h) 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 (processor)
Zone 2: Internal Sensor