IT8718F Information

Just a little information about environmental controller part the ITE it8718f super i/o controller.

It can monitor the tachometer of 5 fans. Each fan Uses a 16 bit binary counter.
Each counter counts at 22.5 kHz. When a FAN_TAC pulse arrives, bits 15-8 are copied
to an eight bit register and bits 7-0 are copied to another eight bit register,
then the counter is reset and starts counting at 22.5 kHz again.
  As a programmer I can make an equation like 1350000/(((bits 15-8 register*256)+bits 7-0 register)*2) to get the fan rpm. The 1350000 is 22.5khz * 60 so I get rpm and not revolutions per second.  The *2 is because my fans have two pulses per revolution.   
ITE named the inputs FAN_TAC1, FAN_TAC2, FAN_TAC3, FAN_TAC4, and FAN_TAC5.

It can monitor 3 temperatures. The temperature values are 8 bit two's-complement -55c to +125c.  Because ite chose to store these temperatures as two's-complement, as a programmer I can just assign the register to a signed byte variable then print the variable to the screen
and it will handle the + and - ok. 
ITE named the inputs TMPIN1, TMPIN2, and TMPIN3.

It can control the speed of 3 fans with pulse width modulation (pwm).
ITE named the outputs FAN_CTL1, FAN_CTL2, FAN_CTL3.

The 3 fan controllers in the it8718f can each be in one of 3 modes.

On/off mode. The fan will be off (stopped) or on (running full speed).

Smart guardian software mode. The fan speed will be determined by the PWM value entered into a register in it8718f by a software program. The pwm value is stored in bits 6-0 of a register. This is 0 for stopped and 127 for full speed.

Smart guardian Automatic mode. The fan speed will be determined by the values in the it8718f registers.

off temperature, At temperatures below this value the fan pwm value will be 0.

start temperature, At this temperature the fan will start with the start pwm value.
start PWM value, At start temperature this is the pwm value the fan will be running at.
slope PWM value, At temperatures above start temperature, for each degree increase in
temperature, pwm value will increase by slope PWM value. This is an 7 bit value. 4 bits for
the whole number part and 3 bits  for the fractional part. this can be from 0 0/8 to 15 7/8.
The fractional part is bits 2-0 of a register.The whole number part is bits 5-3 of a register
and bit 7 of another register.

Direct-down control,  Direct decreasing mode. As temperature decreases the pwm value             will decrease  by the slope pwm value for each degree decrease.  Slow decreasing mode. As temperature decreases the pwm value will not decrease  until the temperature has decreased the value of  temperature interval. Then it will decrease by the slope pwm value.
temperature interval, In Slow decreasing mode this is the value temperature has to decrease before  pwm value will decrease by slope pwm value. This is a 5 bit value, bits 4-0 of a register.

TMPIN1, TMPIN2, or TMPIN3, Each fan controller can use any of the TEMPIN's to control it's fan speed.

My ga-p35-ds3L motherboard uses these values.

off temperature       0
start temperature     20
start PWM value       35
slope PWM value       2.000
Direct-down control   Slow decreasing mode
temperature interval  3

These are just my personal observations. Tom.