I found that extra sensor with Lavalys Everest, and it's similar to
yours. My temps are reported there as:
motherboard 41
CPU 26
"Aux" 36
(The BIOS Hardware reports the CPU to be 36 and the system to be 41)
I suspect that the CPU is 36, the motherboard's 26, and the
southbridge is 41, but I still don't know how to be sure. I just
can't imagine anything on the motherboard being hotter than the CPU
unless it's the southbridge, (You can put your 37°-finger right on the
southbridge's heatpipe receptacle, and it's barely warm to the touch.)
Ron
IT8712F SuperI/O and hardware monitor
LPC based (easier for software to find)
Eight voltage sensors:
Pin98 2 volt for Vcore1 of CPU
Pin97 2 volt for Vcore2 of CPU
Pin96 3.3 volt for system
Pin95 5 volt for system
Pin94 +12 volt for system
Pin93 -12 volt for system
Pin92 -5 volt for system
Pin91 5 volt for VCCH (possibly meaning +5VSB)
Three temp sensors:
Pin89 TmpIn1 Transistor, diode, or thermistor based input
Pin88 TmpIn2 Transistor, diode, or thermistor based input
Pin87 TmpIn3 Transistor, diode, or thermistor based input
If a person wanted to determine what was hooked up, they would
start tracing copper wires from pins 87 through 89 on the IT8712F
SuperI/O chip. The software doesn't know, on the temp inputs,
what type of device is being used. (It would be hard coded in
the BIOS, one would hope.) The software needs to know
the device type (transistor, diode, thermistor), as the voltage
to temperature conversion formula will be different for each.
While ITE attempted to standardize the use of voltage inputs
on pin 98 through 91 (by assigning standard meanings to them,
and implying standard scale factors in use for each one), there
are no standards for the temperature inputs in the datasheet.
http://www.iteusa.com/product_info/PC/Brief-IT8712_2.asp
There is a register that would be set up by the BIOS, that
indicates whether a diode/transistor or a thermistor is
being used on a channel. Now, how do you read the registers
on a chip like that ? That is the question... (This problem
would likely be easier to investigate in Linux, than in
Windows.)
For thermistors, the practice is pretty standard, to use
a 10K ohm thermistor (value at 25 degrees C), and a 10K ohm
resistor to make a voltage divider. The thermistor used also
has a certain beta value (3435?), which seems to be common from
board to board. For the most part, that means a utility
should be able to deal successfully with a thermistor,
if it knows it is a thermistor. (These thermistors are
non-linear devices, so there is a conversion curve - it
looks like the 8712F has a ROM lookup table inside, forcing
the thermistor to be a standard type for sure.)
I don't know right off hand, what math is used for diode type
sensing, but presumably if you trace down the source for
"lm_sensors" or the like from Linux, the method should become
clear.
As for "what do thermistors look like", unfortunately some
of the surface mount ones I've looked at, are not that much
different than ordinary resistors in appearance. If a
thermistor is used in a processor socket, and the socket has
a hole in the center, chances are you'll see the thermistor
in the hole area. For motherboard temps, you'd have to trace
conductors to try and find the thing. Motherboards usually
have four layer stackup (with the odd one using six layers),
so unfortunately not all the copper is visible from the
outside of the board. Good luck figuring it all out
Paul
