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Thread: PC 5170 need help with PAL16L8 and 28S42

  1. #1

    Question PC 5170 need help with PAL16L8 and 28S42

    Hello im new to vintage computers so sorry in advance.
    I am currently trying to make a 5179 clone(just for fun) and i have one small problem.. PCAT Technical Reference has these ic's
    1. PAL16L8 as U130
    2. PAL16L8 as U 67
    3. 28S42 as U72

    As far as i know, PAL's need to be programmed, and 28S42 is a PROM, so also needs to be programmed...
    If anybody knows how to program them(i mean, what data) please tell me, ill appreciate all help
    P.S. Sorry if im doing smth wrong, its my 2 day of going into vintage hardware

  2. #2

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    The data for the PALs could be a problem. AFAIK the PALs have a security fuse that disables someone to read their internal programming. You can still "read" one like a normal (EP)ROM but then you still need some analyzing software to retrieve the functions behind the data.
    With kind regards / met vriendelijke groet, Ruud Baltissen

    www.baltissen.org

  3. #3

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    Thank you, there is also the problem that i dont have original PALs on hand so i cant even make the logic table.. ;-;

  4. #4
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    Maybe someone's done the work. More modern GALs (e.g. 16V can be used for the PALs, and quiet often a GAL with a bit of jiggering can be used for the bipolar PROM.

    But yes, you need to know what was in them to begin with. I suppose you could make a decent guess on them based on analysis of the schematic and their function.

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    Quote Originally Posted by Ruud View Post
    AFAIK the PALs have a security fuse that disables someone to read their internal programming. You can still "read" one like a normal (EP)ROM...
    Since they are combinatorial only, I doubt they are security protected. As you said, you can dump a truth table provided you know which pins are inputs and which are outputs (some are I/O) - which can be inferred from the schematic.

    Quote Originally Posted by Ruud View Post
    ...but then you still need some analyzing software to retrieve the functions behind the data.
    LogicFriday is a great tool for this. But it seems the author's web-site is expired. Still available on CNET.downloads.

    As far as programming, most modern EPROM programmers will also write DIP-socketed SPLDs. I'm a little surprised the logic equations are not already published and well known. Also don't get hung up on PAL vs GAL. The later is just a commercial trademark. Also V series is a superset of L that adds flip-flops. You can use just about any 16V8 as a replacement (such as the common Atmel ATF16V8s stocked at distributors). If there are PALASM equations available, I can convert them to a ATF16V8 JEDEC bit file for you to program (if no one beats me too it). Likewise, if you dump the truth table from the PROM, I'll see if a PAL will fit. I've successfully replaced PROMs on the PCjr motherboard with overhanging 22V10's with ground jumpers before building custom replacement boards that mount a SOIC/TSSOP on a DIP replacement board.
    "Good engineers keep thick authoritative books on their shelf. Not for their own reference, but to throw at people who ask stupid questions; hoping a small fragment of knowledge will osmotically transfer with each cranial impact." - Me

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    But if you don't have the originals, things get harder. I'll wager that IBM blew the security fuses just a matter of routine.

    But yes, dumping combinatorial PALs isn't too difficult--see my blog posts on this from a few years ago, using only a parallel port and some random logic thrown together in an evening.

    I like to use the term GAL as a generic, be it PEEL or PALCE or whatever. Erasable programmable logic.
    Last edited by Chuck(G); January 16th, 2019 at 09:40 AM.

  7. #7

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    Thank you, but the main problem is that i dont have the originals on hand and the EMMA has 14l4 dumps instead of 16l8 for some reason

  8. #8

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    Oh, and, one small question.. can a pal18l8 be replaced with ATF16V8?

  9. #9

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    There is a reasonable possibility that I can help you with the truth table in a couple weeks...

  10. Default

    Sorry - took very long until I got some time to work on this... Managed to make highly flexible adapter for reading different chips that my programmer can't read directly:

    _IMG_0029.jpg

    Another issue was to unsolder those chips from my FRU-6489922 motherboard (type 2) without damaging something. At the moment only U130 done. I don't have enough time to check carefully if the reading has any sense - can see some suspicious data... So for now can check the files - would be interesting to hear your opinion...

    U130.zip


    I used Minilog software to minimize logical equations...

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