PC104+ side by side?


Thread Starter

J. Casault

Due to some fairly unique space constraints in my current embedded design, I would like to mount two pc104+ boards side by side on a backplane and still link up both the pci bus. One of the boards is a video capture card and has a stack position selector switch. Is what I want to do possible if that is the only other card on my "stack"? I looked at the PCI specification, but I couldn't find a maximum trace length?
I personally hadn't done it but I don't think it will be any problem. I've seen some pretty wild PC104 boards over the years, including a Stepper Contoller which was the size of an EBX board using the PC104 as the mating daughter board connection. Those traces were real long and it did not appear to have any affect.

You probably want to hear from someone a little more qualified than me though.

Michael Griffin

I haven't done what you have described, but it sounds similar to what is done on a development backplane. Have a look at Tri-M engineering's web site http://www.tri-m.com/products/pc104.html

The development backplane (DEV104) is likely too big for what you want, but it seems to be employing the same principle as what you are interested in doing. Note that they also sell "bus termination boards" (PC104-T) which are supposed to "enhance" the bus signal quality, and which are recommended for large stacks and for boards used on development backplanes.

There are also connector adaptors to allow you to use a conventional PCI board with a PC/104 CPU board. Some of these are right-angle connectors, which would put the PCI board parallel to the CPU board. This might fit within your application.

Curt Wuollet

I have tried to find info on this as well and what I found was mostly bits and pieces. I should think that as long as you are only going to have the two cards on the bus, it shouldn't be too critical. After all, pin headers are not very impedance controlled. I would probably either omit the ground plane as the pin stack normally has none, or at least have it on the far side. Problem is, it is spendy to experiment with PCBs. I once saw a ribbon cable joining two stacks, but wasn't able to find out exactly what they were doing. Keep us posted.