Actually, it seems that PC/104 signals from many controller boards has
gone to 3.3V even on x86 motherboards - especially those using the
newer embedded processors, such as the AMD SC520 and similar.
Normally, the power lines, VCC, are at 5V, but signals generated by
the controller, such as RD & WR, only drive high to 3.3V. All inputs
to the motherboard would be 5V tolerant.
This has created some problems with older peripheral boards,
especially those using discrete decode logic. A little ringing on the
control lines (especially /IOR & /IOW) create some strange behavior.
Usually a small series resistor on the line coming into the board
would fix the problem - assuming the peripheral board was of your own
design and could be changed. I believe PC/104 was originally spec'd to
have RC termination on the lines, anyway (??)
We never had any problems with peripheral boards that used a CPLD for
decode, even when the motherboard was sourcing 3.3V on the control
lines. I believe all or CPLDs were running at 3.3V with 5V tolerant
inputs, anyway.
That said... we were never able to get any of our PC/104 periperal
boards running reliably with a TS-7200, though admittedly, we didn't
put much time into finding out why. We may look to revisit this soon,
since we have a number of upcoming applications that would go well
with the board.
Any insight would be appreciated.
Frank
--- In "pickanameanditstakensoihavethis"
<> wrote:
>
> you mean the 4 x 74lvc245's that according to the schematic are
> driven with a 3.3v vcc and that only covers the 16 data and first 16
> address lines
>
> dave
> --- In Curtis Monroe <> wrote:
> >
> > The pc104 uses 5 volt logic, you can see the 3.3 volt to 5 volt
> interface
> > chips near the power supply pins on the board (4 of them there).
> >
> > -Curtis.
> >
> >
> >
> > On December 5, 2005 11:20 am, pickanameanditstakensoihavethis
> wrote:
> > > hi
> > > i have just been looking through the diagrams and documentation
> > > for the ts7200
> > >
> > > my first assesment of the pc-104 was that the logic levels
> where at
> > > 3.5v logic levels and not at 5v logic levels but on a second
> look
> > > the levels for the pc-104 bus are not stated
> > >
> > > having 5v on there i suppose supports legacy devices ,but they
> > > appear to be driven using 3.5v logic
> > >
> > > some of the lines look buffered but some are not , rather than
> > > make assumptions on this i thought i would be better asking
> > >
> > > i am currently working on a custom pc-104 expansion card that
> is
> > > going to be easier to interface with 3.5 v logic levels
> > >
> > > dave
> > >
> > >
> > >
> > >
> > >
> > >
> > >
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