"440bx design guide" - PDF pg.30
http://www.intel.com/design/chipsets/designex/29063401.pdf
"GTL+ is a low output swing, incident wave switching, open-drain
bus with external pull-up resistors that provide both the high
logic level and termination at the end of the bus."
One purpose of the resistors, is to function as the load
resistor and also as a transmission line termination, to
reduce signal reflections. If R3 is a 56 ohm resistor, perhaps
that is its purpose.
A good technical article on modding, should explain what each
of the modifications is doing, and what the old connectivity
achieved before the modder cut it up. Such information makes
it possible for a third party to check the workmanship of
the modder, and interpret what he/she is doing. Since Mr. Sassen
chose not to help us in that way, it is hard to say what he
has done.
For example, I don't understand why Mr. Sassen has connected
a 56 ohm resistor to ground. It could be that this grounding
resistor is physically underneath where R3 is located on
the other side of the board. In other words, a signal used
to have a 56 ohm resistor to Vtt, and now it has a leaded
resistor connected to ground, on the other side of the board,
as a modification. A 56 ohm resistor might make a good high
speed termination for some kind of logic, but if the signal
on that line is GTL+, a pullup resistor to Vtt makes a lot
more sense.
Without a schematic diagram or a block diagram of what he has
done, I would need the module in my hands to figure out what
has been done.
With regard to the voltage being requested, use an ohmmeter
to see if there is continuity from the VID pins in the socket,
to the SC242 edge connector. It could be the slocket doesn't
have them wired, or there is a DIP switch or something ? Are
you sure the slocket doesn't have a way to modify the VID
value ?
This article describes how to do a "wire trick", in a situation
where there is no DIP switch to set the Vcore voltage. When
I needed to do a mod like this, I just cut the appropriate
VID tracks near the edge connector, and wired the signals as
required. (I modded a slocket that had no VID jumpers.)
http://www.tipperlinne.com/p2b-ds.htm
Other info:
http://developer.intel.com/design/chipsets/440/documentation.htm
(A dual processor 440BX motherboard schematic. This will not
teach you much, as the real action is on the slocket. Still,
this is one of the few reference schematics available for
download.)
http://www.intel.com/design/chipsets/designex/BXDPDG10.PDF
Paul
