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ISA SBC in unpowered ATX motherboard?

Started by Ghazan Haider March 24, 2004
Hi all,
Can ISA SBC cards (full or half) be plugged in unpowered AT or ATX
motherboards to act as passive backplanes, given the SBCs themselves
are powered properly?

On a related note, can two SBCs contact each other if theyre in the
same backplane? How do they elect the active one?

Lastly, can you plug in ISA cards in the backplane and expect the SBC
to be able to use it?


I'm sorry i dont have much experience with this platform, but have
access to some fast SBC cards with some potential. Has anyone tried
say a 486 or even an AT-XT motherboard?
Ghazan Haider wrote:

> Hi all, > Can ISA SBC cards (full or half) be plugged in unpowered AT or ATX > motherboards to act as passive backplanes, given the SBCs themselves > are powered properly? >
No. The bus drivers will power up (your SBC power is connected directly to the motherboard power) and conflict with the SBCs drivers. Passive backplanes are cheap enough, though. By the time you've hacked the board to pull them out, you will have spent more in time than the cost of a proper backplane, and you will still be powering all the redundant circuitry of the motherboard.
> On a related note, can two SBCs contact each other if theyre in the > same backplane? How do they elect the active one? >
There's no bus mastering in ISA, so no.
> Lastly, can you plug in ISA cards in the backplane and expect the SBC > to be able to use it? >
Yes, providing it is a passive backplane and you use the appropriate API. Paul Burke
Ive seen the backplanes are just wire connections for the most part,
so a powered SBC in an unpowered motherboard should be able to use
another board in another slot. This will work if the turned-off chips
on the desktop motherboard do not leak current between the pins in
ISA.

This is something I have to try, and will post back the results. I'm
trying to plug in a Pentium2 SBC (powered directly) in an unpowered
motherboard along with other ISA cards.
"Ghazan Haider" <ghazan@ghazan.haider.name> wrote in message
news:2f57764a.0403260901.3a71f3bb@posting.google.com...
> Ive seen the backplanes are just wire connections for the most part, > so a powered SBC in an unpowered motherboard should be able to use > another board in another slot. This will work if the turned-off chips > on the desktop motherboard do not leak current between the pins in > ISA.
Forget it. If the bus is loaded with unpowered motherboard chips, any signal from your SBC to the bus effectively powers the motherboard chips through their substrate diodes. A real backplane as used in industrial PC is indeed just a bunch of tracks between the connectors. Meindert