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GALs and old PCBs

Discussion in 'Electronic Basics' started by matt, Feb 21, 2006.

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  1. matt

    matt Guest

    I've having some difficulties using a GAL on a 25 year old PCB - I
    have the correct JEDEC file and my programmer will handle the GAL okay
    (a GAL16V8D-25QPN) but the board won't work with the newly programmed

    Why is this likely to be?

    Something to do with the type of GAL or perhaps even the speed?
    (although I would have though that a -25 would be fine for a 25 year
    old PCB).

  2. Deefoo

    Deefoo Guest

    -25 is for speed, not for age ;o)

    There is no reason to assume that your GAL would be of the right speed for a
    25 year old PCB. Your GAL may be too fast or too slow. Don't you have the
    original GAL?

  3. matt

    matt Guest

    I know that. :)
    No - the original chip was an 82S153 PLD, it's just that someone
    converted the contents of that to JEDEC format to work with a modern
    GAL (82S153's are hard to find and expensive). It worked for him, just
    can't figure out why it won't work for me.

    So perhaps I should buy and try a faster GAL? -15 perhaps? -10? -7?
  4. Sambo

    Sambo Guest

    Ah, pals and gals maybe I'll still get a chance to play with those.
    I would say you are most likely already way too fast, 250-300ns RAMs in those days, 82S153 probably had propagation delay of at least 40ns come to think of it it is not even PLD it is a PROM hence even larger propagation delay can be expected. A quick glance on goole, I don't see anythink with specs ( so many useless hits these days $#*%^& ) It is not in the "CMOS cook Book" must be in "TTL Cook Book" anybody have it handy?
    Of the top of my head I don't even think it has an enable signal which you could .....
    The old slow part may be bridging the time the inputs stop being valid and the outputs are read (since I don't believe the part has output enable), the only way would be to buffer the outputs or use a device that could delay the outputs internaly.

    Why it worked for the other person (with same circuit, same speed and type GAL ) can't say. Maybe you can get a bit slower GAL and get lucky.

  5. Maybe. But I'd be mistrust the conversion in the first place. Do you have
    the JEDEC of the original 82S153? If memory serves, AMAZE can convert the
    JEDEC back to logic equations so you can see what it is supposed to do. Once
    you know that you can edit the source for a GAL and get the right JEDEC for

    petrus bitbyter
  6. matt

    matt Guest

    Afraid not, no. :(
    The problem then, for me at least, is understanding them. :)
    So the equations would then be converted back to a JEDEC file?
  7. matt

    matt Guest

    Hmmm, thanks. Wish I could find a slower GAL! Do they still exist?
    That's the problem - any ideas where from? :)
  8. Ben Jackson

    Ben Jackson Guest

    If the edge rate of the new GAL is too fast you could try putting 100
    ohms or so inline with the new chip (build a small daughter card, perhaps).

    But since you say it works for someone else, perhaps most likely is
    that some other part of your 25 year old board is bad.
  9. Sambo

    Sambo Guest

    Is it really everything identical as the other person is doing?
    Even metal plate (grounded or not hmm) under the circuit could possibly make a difference.
    Do you have the schematic? Converting to new pals, sounds like something I read a while ago with regard to fixing an old video game.
    Sounds like you are programming the PAL yourself so you must be able to make a circuit board that would plug in place of the PAL and contain the new GAL 74??374 or 74??574 for the outputs and hex inverter to delay some clock signal . I maybe wrong and there is an enable input which you'd run through the inverters and to the clock of the ...... well this is already going in the wrong direction hehe.
    Maybe it is more trouble than it is worth.
    I could be done, but very difficult without deriving the timing from the board.
  10. matt

    matt Guest

    Would that just be on the outputs though?
    The board is okay as it works with the original 82S153 (which I can't
    dump and don't have a replacement for - I'm testing the GAL on this
    board but it will be going on another board (same type) as that one
    has a bad 82S153).

    I'm guessing that that guy who created the JEDEC file (a few years ago
    now) used a slower GAL.

  11. matt

    matt Guest

    Yup, except maybe he used a slower GAL? I don't know, just guessing.
    No, seems to be except the same I'm afraid.
    Yes, the schematic can be found here:

    However, it's a 12MByte file as it's the complete manual - the schems
    are towards the end of the PDF, you'll need to look at those for the
    Memory Board. The device is question is the PLS at location U10

    BTW, the quality of the schems is poor in places, but just about
    It's a GAL. :)
    Yes, maybe. Depends if it would work or not, and not sure if I could
    do it without exact instruations on what to connect to what.
    I see. Hmmmm, wish I could find a slower GAL. :)

  12. matt

    matt Guest

  13. Sure, but JEDECs differ widely for different components. They often even
    differ for the same component type but other manufacturer.

    As for the speed itself I shouldn't expect problems. According to the
    Philips datasheet the standard N82S153 is rated for 40ns, the N82S153A is
    rated for 30ns. So your 25ns GAL may be too fast rather then too slow. But
    in that case I consider it either a poor design or the use of some special
    trick. Which will not help you, I'm afraid.

    BTW It worked for someone else. Do you mean same board, same 82S143 content
    and same object GAL? (So same type and brand?) Any idea what the GAL is
    supposed to do? Any problem posting the JEDEC(s) you have? (Part of) the

    petrus bitbyter
  14. matt

    matt Guest

    Really? Ugh - confusing!
    Same board, yup (well, same design, same manufacturer, etc).
    Same GAL type: GAL16V8D - not sure what speed or brand he used though
    as he's not replying to his emails.
    I'll quote from the chap who came up with the JEDEC:

    "All ROM and RAM on this Memory Board is initially decoded by the
    82s153 FPLA at location U10. The FPLA enables address decoders based
    on the upper 3 address bits of the address bus. Additionally, the FPLA
    prevents ROM and RAM access during certain system processes including:
    refresh cycles, active resets, I/O requests and a architecture
    specific signal called /BUZOFF. The FPLA contains 5 address inputs and
    7 status line inputs. Outputs of the FPLA are 4 decoder enable lines
    and 1 transceiver direction select line. The enable line for ROMs X1
    through X4 (74LS139 at U8, pin 1) is selected on addresses x0000-x3fff
    ( !a15, !a14). The 4 ROMs are then selected off of a13 and a 12 by the
    lower half of the 139 decoder at U8. All the other selects work
    similarly. The second half of U8 (pin 15, enable) selects ROMs X5-X8
    (a15, !a14), the lower half of U9 (pin 1, enable) selects the ROMs at
    X9 and X10 (a15, a14, !a13)and the upper half of U9 (pin 15 enable)
    selects one of the 4 RAMs (a15, a14, a13) based on address lines a11
    and a12).

    The FPLA also selects the direction of the 74ls245 transceiver at U17.
    On a write, pin 1 of U17 is held high to allow data to flow from the
    processor data bus to the RAM/ROM board data bus, on a read the line
    is held low and the data flows in the opposite direction. Most of the
    additional circuitry on the ROM board deals with selecting the RAM at
    X21 for high score and setup information. The three 74ls244s at U16,
    U15 and U 11 are all used as line drivers with all of their select
    lines tied low permanently.

    The original FPLA used is a Signetics 82s153, which is now obsolete, a
    modern replacement is a Signetics pls153, however I have not been able
    to get a good copy of one so I had to write a replacement using a PLD
    Here it is from the guy's site:
    I don't know how to extract a page or two from a PDF, but the whole
    manual (12 MBytes! with schems at the end) can be found in this file: Arcade Manuals and Schematics/Robby Roto.pdf

    you'll need to look at the for the 'Memory Board'. The device in
    question is the PLS at location U10

    BTW, the quality of the schems is poor in places, but just about

    Many thanks. :)
  15. Rich Grise

    Rich Grise Guest

    You can draw a box around it, copy it to the clipboard, and paste it into
    a paint program and save it as a .gif, then link to _that_. :)

    Good Luck!
  16. Rich Grise

    Rich Grise Guest

    Can't dump it? Can't you plug it into a breadboard, put a counter on
    the inputs, and see what you get at the outputs?

    Then you would at least have a truth table, unless it's got some kind
    of embedded state machine or something. It'd also help to know if
    the outputs are latched or anything. Is there a data sheet anywhere
    on the 82S153?

    Good Luck!
  17. matt

    matt Guest

    Only if I knew exactly what I was doing. :)
    There's one here:

    Thanks for your help! :)
  18. matt

    matt Guest

    Good point but I have no webspace - where would I upload it to?
  19. Sambo

    Sambo Guest

    LOL, rotorooter? Let us know when you are fixing at least burger time hehe.

    The most suspicious signal is the last (bottom) output controlling the U17
    as someone suggested, resistor may work. Two transistor driver ( optionally with RC on input ) or run all outputs through 74L244 (L only, if it exists) although that only adds about 12ns, 'L' would probably be about 20ns.
    I'd try the following, adding R1( and C1 only if needed, start in center position and reduce.

    +5V ----------------------
    | |
    R1 |-| -
    -------- 2.2K | | 510-1K | |
    from PLA 13 ----| 1K |----| | | | |
    -------- | T T
    ^ | 2.2K | |
    | | --------- |/ ----- |/-----PPLA 13 socket
    -------*-----| |----| |-------|
    | --------- |\ |\
    C1 | V V
    100pf ===== | 2x2n4401 |
    ===== | |
    | | |
    | ===== =====
    | === ===

    Or if using R1 C1 drop the second transistor with its resistor , put 1-1.5 K resistors
    between collector and +5 and emitter and GND and take the signal from the emitter. However, this may not be a good idea for a digital circuit (slow rise time).

    Now fire up that slow comp and it is time for a little Major Havoc, hehe.

  20. matt

    matt Guest

    Close - Robby roto in fact. :)

    Excellent, thanks - I'll make that up and let you know how it goes.

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