F71872
Fan Speed mode
Fan speed mode is an intelligent method according to expected fan speed pre-setting by BIOS. In the
beginning, fan speed will be operated at full speed and the F71872 will get the full speed count value. After
that, the fan speed will automatically rotate according to the expected fan speed setting by BIOS. For instance,
the register CR69h and CR6Ah are used for this mode of FAN1.
Temperature mode
At this mode, F71872 provides the clever system to automatically control fan speed related to
temperature system. The F71872 can provide three temperature boundaries and three intervals for user
setting, and each interval has its related fan speed count. All these values should be set by BIOS first. In the
F71872 design, the F71872 will auto-generate temperature boundaries (average value) between those
boundaries that user setting, and it will auto-produce interval fan speed count (average value) between users
setting value.
If the temperature value is set to 40, 50 and 90°C, it will auto-generate two temperature boundaries value
of 45°C (This value is calculated automatically by hardware design of the F71872. (450+40)/2 =45 ) and 70°C.
The same way, the related desired fan speed counts for each interval are 4200RPM, 3600RPM, 3000RPM,
2500RPM, 2000RPM and Stop Counts. When the temperature is within 50~70°C, the fan speed counts will be
3000RPM (Registers CRA4h~CRA9h, CRB4h~CRB9h and CRC4h~CRC9h). The F71872 will auto-adjust
PWMOUT (PWM_DUTY) to make fan speed match the expected value. It can be said that the fan will be
turned on with a specific speed set by BIOS and automatically controlled with the temperature varying. The
F71872 will take charge of all the fan speed control and need no software support.
Desired Counts (RPM)
4200
90 Degree C
3600
70 Degree C
3000
50 Degree C
2500
45 Degree C
2000
40 Degree C
Stop Counts
Auto-Generated
(Average value)
Auto-Generated
(Average value)
PWMOUT Duty-cycle operating process
In both “FAN SPEED” and “TEMPERATURE” modes, F71872 adjust PWMOUT (PWM_DUTY1 (CR6B)
of Fan1, PWM_DUTY2 (CR7B) of Fan2, PWM_DUTY3 (CR8B) of Fan3) duty-cycle according to current fan
count and expected fan count. It will operate as follows:
21
July, 2007
V0.28P
FINTEK [ FEATURE INTEGRATION TECHNOLOGY INC. ]
