Topaz wrote on 2024-07-06, 13:10:I have a sound blaster CT2800 but its missing all the parts for the IDE half I have all but 1 IC witch is U4 I don't know if it […]
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I have a sound blaster CT2800 but its missing all the parts for the IDE half I have all but 1 IC witch is U4 I don't know if its a 74lsxxx IC? I cant see it from any pic on the web or some kind of "GAL or PAL" if so looks like ill be SOL
U1 - 74LS245
U2 - 74LS245
U3 - 74LS224
U4 - ???
Your list has a typo. U3 is as '244, not a '224. But you are completely correct that U4 is a custom logic chip. That chip is used to recognize the IDE base address of 170/168/1E8 according to the jumper settings. If you want to get into developing custom PAL equations yourself, this would be a perfect entry-level project. The desired behaviour of the PAL can easily be deduced from the ISA protocol and the trace layout on the SB16 card - so it clearly requires some basic level of hardware reverse engineering to get it done. Otherwise, you could try to look for scrap SB16 cards that have this PAL equipped to use them as donor boards. If you are lucky, some chinese electronic component dealers already have some of those chips in stock, taken from cards like the one on your photo. On the plus side, that PAL/GAL has a custom Creative Labs marking on it, so you might find identical chips by looking for the type number (yet I failied to find enough good photos to make out which part of the chip label is a type identifier. It does not seem to have the usual CT+4 digits pattern, which would make the type identifier obvious. On the down side, a single PAL like this is probably not worth the effort, shipping costs, and the risk to get a chip with fake markings, which means that essentially, you might indeed be SOL.
