Hi: * Jean Delvare <khali at linux-fr.org> [2008-02-18 16:38:58 +0100]: > On Mon, 18 Feb 2008 16:20:21 +0100, Per Jessen wrote: > > Jean Delvare wrote: > > > > > Depends on the thermal sensor type. For thermal diodes (or > > > diode-connected transistors) the chip can typically detect if the > > > thermal sensor is missing, and it will report it either explicitly in > > > a status register, or through an arbitrary value (typically -128 or > > > +127). > > > > > > For thermistors, what the chip measures is actually a voltage, which > > > is then converted to a temperature value. If the board manufacturer > > > doesn't want to implement a sensor, they will typically wire the input > > > to the ground, which is equivalent to an infinitely high or infinitely > > > low temperature (depending on how the voltage divisor bridge is > > > built), and the chip doesn't have to treat this as a special case. > > > Things get bad when the manufacturer leave the thermal input floating, > > > you will get random temperatures. This is quite possibly what Per is > > > experiencing. > > > > Hi Jean > > > > if only I was getting random readings, but the readout I'm seeing > > doesn't look random at all - it's typically 80-81, but will increase to > > 86 when I'm stressing the system (the CPU-temp will rise to 62/63 at > > the same time). > > Well, if it seems to make some sense, it might as well be wired. > However, 80?C is rather high, and I would hope that no chip on my > motherboard gets this hot. But depending on the hardware, it might > actually happen. Note: "floating" doesn't necessarily imply "random". A floating input could still show some small correlation with other circuits in close physical proximity. Regards, -- Mark M. Hoffman mhoffman at lightlink.com
