Hi Krzysztof, On Wed, 04 Jul 2007 09:25:05 +0200, Krzysztof Helt wrote: > According to docs, the THMC50 produces range between 0 and 2.5V. > The residual voltage (0 value != 0 V) comes from the external > power amplifier. There are 6 example designs of external power > amplifier given in the THMC50's datasheet. Most of the are > powered by 0 - 12V so they are usually unable to produce the full > 0-12V swing (as amplifiers and transistors cannot give output up > to power voltage limits). One design (the cheapest) is said to > not give full voltage swing by design. That's why they have the > fan off bit - to be able to stop the fan. > > One of designs is powered from +/-12V and this one certainly can > produce true 0V output - in such case the 0 value would stop fan > and the fan off pin may be left unconnected. As you can see, my > driver writes 0 value into the fan speed register along with > setting of the fan off bit - to cover both cases. > > The residual voltage is simple imperfection of analog parts > outside the chip and the value of this voltage is as random as > the choice of analog elements mounted on motherboards (will vary > with production batch change and type of elements e.g. change of > supplier). > > Summary: one knows that 0 value produces 0V at the chip pin and > at the same time one knows it is not 0V at the fan pins in most > of reference designs (hence the separate fan off bit). I see, thanks for the detailed explanation. Then I'm fine with your implementation. -- Jean Delvare
