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Tutorial on Programmable Logic Devices?

Discussion in 'Electronic Basics' started by Dave Nubury, May 22, 2005.

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  1. Dave Nubury

    Dave Nubury Guest

    Can anyone point me in the direction of some tutorials on PEEL's.

    I just picked up a couple of Z80 processor boards on EBay. I was going to
    try and i/o / memory map the board by tracing the IC's
    until I ran into a few of these suckers. Looks like they are being used for
    decoders. I've got to try and figure out how they
    are programmed so I can make sense/use of my controller board. I downloaded
    a .PDF for PEEL18CV8P, but I'm still confused.
    Is there any easy way to figure out how they are programmed?

    Thanks,
    Dave
     
  2. Rich Webb

    Rich Webb Guest

    They are generally programmed with a hardware description language (HDL)
    like VHDL, ABEL, CUPL, ... Looking at the fuse map would allow you to
    trace out the functions but, like having disassembled program code into
    bare assembler instructions, you'll still have some work to do to
    understand it. You'll need a gizmo like
    http://www.needhams.com/products-EMP21.html to read it.

    Note that if they've burned the security bit, you will not be able to
    read the fuse map. All you can do is look at the goze-ins and goze-outs
    and take it from there.

    If you assume that the designers didn't intentionally obfuscate things,
    then you can probably work out the intended behavior by what it connects
    to.
     
  3. ------------------
    If all they are is address decoders, then they are static logic,
    with no dynamic/sequential logic contributions, in other words,
    a simple gate array with no feedback loops. That means you can
    map them by simulating inputs to their inputs and watching their
    outputs.

    But if they are not, then lots of luck! I have the specs on
    programming 18V8 Peel devices, but again, if the security is
    set, you have only external testing to arrive at their gate
    circuit equivalent. You could go through random addresses and
    write a program to look for any outputs that have differing
    results with the same inputs, and that would fine any sequential
    logic statements.

    -Steve
     
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