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Thread: PC 5170 need help with PAL16L8 and 28S42

  1. #21
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    That's an annoying thing about the blog section--there is apparently no way for one to remove entries made in error--mostly by clicking the "blog this post" instead of the "reply to thread" right below it. I don't really understand why the "blog this post" button is there to begin with.
    Last edited by Chuck(G); August 23rd, 2019 at 10:25 AM.

  2. #22
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    Quote Originally Posted by Dwight Elvey View Post
    Nice but what about 3state outputs?
    Dwight
    I address this in the later parts of the blog. I employ a little trick to gently "push" on outputs to determine if they're tristate. If I gave more thought to this in retrospect, I could have worked the "push" logic with just a single output. In other words, run the exhaustive test of combinations with and without the "push" and compare the results.

    However, I've had no need to clone PALs in quite a few years, so this has dropped off the radar for me.

  3. #23

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    Quote Originally Posted by Chuck(G) View Post
    I address this in the later parts of the blog. I employ a little trick to gently "push" on outputs to determine if they're tristate. If I gave more thought to this in retrospect, I could have worked the "push" logic with just a single output. In other words, run the exhaustive test of combinations with and without the "push" and compare the results.

    However, I've had no need to clone PALs in quite a few years, so this has dropped off the radar for me.
    I guess I got tired of pushing next. Most applications don't use the 3state anyway. They are usually just address decoders.
    Dwight

  4. #24

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    So nobody has made copies of the PAL's on the 5170? I'd sure like copies to burn if they have so I can have them on hand if needed. Best I can tell there are 3 of these on the 5170 type 1 board.

  5. #25

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    Quote Originally Posted by eeguru View Post
    I also ran U130 through LF and got the same minimizations.

    Code:
    IRQ13 = ERRORn' ;
    BUSY286n = 0;
    NPCSn = XA3' + INTAn'  + CS287n  + SMIO ;
    RESET287 = INTAn CS287n' SMIO' XIOWn' XA0 XA3' + RESET ;
    Every book i read on this topic says that the BUSY Pin of the 287 coprocessor should be connected to the BUSY Ping on 286. I checked the schematics and your guys' Truth table and it seems that,
    1. The BUSY Pin on 286 is always 0 which would mean: always active
    2. The BUSY Output signal of 287 would not be routed to anything except input to U130 and as such it would be useless.

    Can anybody help me understand this part of PC AT schematics?
    Thanks

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