I'm designing a new ISA form factor PC board for a legacy system. I've looked around the net and found several references for ISA board dimensions, but they don't call out the location of the edge card connector fingers with respect to the front panel edge of the card.

Does anyone know where to find a reliable ISA board outline, including the relative location of the edge card contacts to the front panel edge?

One possible source of the mechanical specificaitons is IEEE P996, a proposed standard for the ISA bus that was apparently never finalized, but it does not seem to be available any more.

  • \$\begingroup\$ found this .... interfacebus.com/Design_PCAT_Card.html .......... what do you mean by front panel edge of the card? \$\endgroup\$ – jsotola Nov 6 '18 at 22:07
  • \$\begingroup\$ @jsotola In that drawing, it would be the right hand edge. The drawing only gives the outline dimensions, but not the location of the edge connectors with respect the outline. I'm also looking for more of an original/trustworthy source \$\endgroup\$ – crj11 Nov 6 '18 at 22:09
  • \$\begingroup\$ I think part of the problem is that it never was a standard. I suspect that serious ISA board designers (aside from people working at IBM) had a drawer full of boards and a decent caliper, and their own personal drawing. IIRC, the connector captures the tab pretty well, and the bracket allows for some slop -- if you can find a spec for the connector it should spec the tab, and if you get the bracket a little bit wrong you should still be OK. \$\endgroup\$ – TimWescott Nov 6 '18 at 22:49
  • \$\begingroup\$ maybe the best thing to do is to find a scrap computer that contains some ISA boards and measure the boards \$\endgroup\$ – jsotola Nov 6 '18 at 23:23

There may very well be a outline in the original PC-XT and/or PC-AT Hardware Reference Manual, mine were 3 ring binders. A lot of the circuit diagrams for the add on cards were included. These may be for sale second hand somewhere.

I remember using the dimension data from a instruction sheet from a Universal breadboard card that was sold by RS components (of UK, not the US Radio Shack) for this purpose. See if someone is still selling a prototyping card with decent documentation online.

You should be able to get adequate accuracy by measuring half a dozen diverse samples as the tolerances were huge or ignored. Very rarely was a card a tight fit and sometimes they did require loosening of the back plate to make them fit well.

In fact you r easiest is to search the net for a few PCB layouts or Gerber files and use them for reference.


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