Messages in this thread |  | | From | Marek Michalkiewicz <> | Subject | Re: serial ports | Date | Mon, 5 Aug 1996 19:33:38 +0200 (MET DST) |
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Magnus Hiie: > Why is it impossible for multiple (standard) serial ports (ttyS?) to > use the same IRQs?
It's a hardware limitation of the ISA bus. Multiple ports on the same card can share the same IRQ if they can be logically OR-ed. But multiple ISA cards can't use the same IRQ line at the same time - they have three-state outputs which can't do wired-OR (if one of the outputs is high and the other is low, the result is undefined - might work with some combinations of cards but don't count on it). It's one of these things IBM screwed up in the original PC and it is difficult to change it now because of "backward compatibility" (EISA and PCI finally got it right but ISA is still quite common).
Hope this helps.
Marek
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