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linuxlove
April 7th, 2011, 06:12 PM
The PS/2 Model 25 is a great little all-in-one XT system. The only problem is there are only two ISA slots.
I've seen pictures of XT motherboards and the traces going to the ISA slots look like they just run through the same pin on all the ISA slots.
Would anyone be willing to take a high resolution scan of the underside of an XT motherboard in the ISA section so I can see how the traces are laid out?
And would it be possible to add more ISA slots to the Model 25?

Ole Juul
April 7th, 2011, 07:38 PM
. . . And would it be possible to add more ISA slots to the Model 25?

The PC has an extender box as an option. Would one of those would work if your '25 is an 8086? I've got the cards but not the cable. Anyway, at that slow speed perhaps a shielded cable with plain connectors at each end will be good enough to go the 18" or so that you need to stick a couple of cards in another box. I don't know how much the little PS will supply, but that could need a boost.

Chuck(G)
April 7th, 2011, 07:52 PM
You can probably get PCB trace layout from the Big Blue Seed book (ISTR that there's some artwork there). Basically, all the traces are tied together, with heavier traces for the power supply and ground lines. ISA is pretty primitive as buses go.

The trick is not to make the bus lines too long. About 1 ft. is the limit before things get difficult.

If you're cramped for space, you might want to consider PC/104 (ISA bus in miniature).

IBMMuseum
April 7th, 2011, 08:04 PM
The PS/2 Model 25 is a great little all-in-one XT system. The only problem is there are only two ISA slots.
I've seen pictures of XT motherboards and the traces going to the ISA slots look like they just run through the same pin on all the ISA slots.
Would anyone be willing to take a high resolution scan of the underside of an XT motherboard in the ISA section so I can see how the traces are laid out?
And would it be possible to add more ISA slots to the Model 25?

The 8086-based Model 25 riser is as lengthy as the 8086-based Model 30 (with a battery on the riser for the RTC, and three slots), but of course there is no room, and they don't seem to be interchangeable. On the 25SX (which had a proprietary high-density riser slot on the planar) there is a reversed third slot, for either of two special NICs, Token Ring or Ethernet. Eduquest models had five ISA slots, two were reversed (for one of the 25SX NICs, and an MWAVE sound card).

luckybob
April 8th, 2011, 12:01 AM
I have an ISA/pci backplane that I use for my single board computers. The ISA slots are wired in perfect parallel. A quick search of ebay revels a LOT of relatively cheap options. such as:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220672073405

The problem would be getting or making a card that will let you wire it all up. :P