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Thread: TRS-80 diagnostic/ICE card

  1. #1
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    Default TRS-80 diagnostic/ICE card

    I have a very sick model 1 that is proving to be a pain to repair due to cut tracks and other issues due to old bad mods (not mine).

    I'm toying with building a card that will plug onto the expansion connector (possibly cpu socket) to allow an external processor to manipulate the board for diagnostic purposes.
    Effectively an in circuit emulator that can diagnose ROM, RAM, video or bus issues. I know how to build the hardware and writing the code shouldn't be a problem but I've not laid out a pcb before.

    I'm split between using a z80 with ROM, RAM a handful of ttl chips and a 16x2 LCD display or an 8951 with a few ttl chips using a serial link as the interface.

    What I'd like to know is there any interest in owning such a beast and is anyone interested in collaborating on designing and producing the hardware?

  2. #2

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    Quote Originally Posted by David_M View Post
    I have a very sick model 1 that is proving to be a pain to repair due to cut tracks and other issues due to old bad mods (not mine).

    I'm toying with building a card that will plug onto the expansion connector (possibly cpu socket) to allow an external processor to manipulate the board for diagnostic purposes.
    Effectively an in circuit emulator that can diagnose ROM, RAM, video or bus issues. I know how to build the hardware and writing the code shouldn't be a problem but I've not laid out a pcb before.

    I'm split between using a z80 with ROM, RAM a handful of ttl chips and a 16x2 LCD display or an 8951 with a few ttl chips using a serial link as the interface.

    What I'd like to know is there any interest in owning such a beast and is anyone interested in collaborating on designing and producing the hardware?
    I'd be interested in one for sure. In fact, the EI is half the equation so if you can also test that consider it.

  3. #3
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    Quote Originally Posted by Tibs View Post
    I'd be interested in one for sure. In fact, the EI is half the equation so if you can also test that consider it.
    I don't have an EI, but assuming they use the same expansion pinout as the keyboard unit then there is no reason both cant be tested.

  4. #4
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    Quote Originally Posted by David_M View Post

    I'm split between using a z80 with ROM, RAM a handful of ttl chips and a 16x2 LCD display or an 8951 with a few ttl chips using a serial link as the interface.

    What I'd like to know is there any interest in owning such a beast and is anyone interested in collaborating on designing and producing the hardware?
    Id lean towards the second option as (if I understand right) it's going to be more flexible - the main logic sits at the other end of the serial cable?

    Definitely interested.

    PJH

  5. #5

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    I suspect this would be a strong seller if it can diagnose a significant number of issues. You should put up a poll.

  6. #6
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    Quote Originally Posted by pjhacnau View Post
    Id lean towards the second option as (if I understand right) it's going to be more flexible - the main logic sits at the other end of the serial cable?
    PJH
    For simplicity I like the 8951 option, however taking that path loses the automatic refresh cycles built into the Z80.
    DRAM testing becomes a problem without the refresh cycles and adding them with extra hardware would require a fair amount of effort.

    The biggest problem is I'm moving house in 2 months and need to begin sorting/packing 25 years of accumulation. It will mean packing all my hardware and test gear so the hardware side of it will be delayed. Developing the firmware for it I can do up until the 11th hour. Anyone interested in putting together the hardware side of it? I can pretty much describe in detail the circuit for a z80 based version, so it would mostly be a task if implementing the finer details such as pcb layout and actual pin interconnects.

    I was sent a link to this project, it suffers from the DRAM issue and it exercises the bus fairly statically so its unlikely to find any speed related issues. On the plus column it is quick, easy and cheap to make.
    http://fjkraan.home.xs4all.nl/digaud/arduino/Z80exer/

  7. #7
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    This might prove useful to some of you. I wrote this ROM originally to aid in repairing a TRS80 clone, but it works just as well in a TRS80.
    Just burn the ROM image into a 2732 eprom and put in socket z33. It does not require working RAM, although faulty video RAM does make the results less readable

    Untitled-2.jpg

    Rom image
    https://drive.google.com/open?id=1M6...-88_ZlzZyyDvCh

  8. #8
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    Quote Originally Posted by David_M View Post
    The biggest problem is I'm moving house in 2 months and need to begin sorting/packing 25 years of accumulation.
    AAAAARRRRRRGGGGGGHHHHHHH!!!!!!!!!!

    You have my deepest sympathies.

    I was sent a link to this project, it suffers from the DRAM issue and it exercises the bus fairly statically so its unlikely to find any speed related issues. On the plus column it is quick, easy and cheap to make.
    http://fjkraan.home.xs4all.nl/digaud/arduino/Z80exer/
    I do like the fact it "exorcises" the computers. I know several of mine are haunted.

    Maybe I'm missing something here but can't you program up the refresh cycles? Even a little 16MHz processor should have the spare cycles to reliably trigger them.
    .
    How did the ICEs of the '80 handle this? A quick google for information on period ICEs doesn't turn up anything useful.

    PJH

  9. #9
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    Quote Originally Posted by pjhacnau View Post
    AAAAARRRRRRGGGGGGHHHHHHH!!!!!!!!!!

    You have my deepest sympathies.



    I do like the fact it "exorcises" the computers. I know several of mine are haunted.

    Maybe I'm missing something here but can't you program up the refresh cycles? Even a little 16MHz processor should have the spare cycles to reliably trigger them.
    .
    How did the ICEs of the '80 handle this? A quick google for information on period ICEs doesn't turn up anything useful.

    PJH
    Some of the simpler ones used a z80, others were quite complex and used a lot of hardware to do the refresh.

    The Z80 does a refresh cycle between each instruction, 16Mhz might seem fast but that only gives 8 single clock instructions for an interrupt routine not nearly enough to setup the output pins.
    It might be possible to do a slower refresh but I suspect it will require significant rewriting of the code and have no guarantee of success.

  10. #10
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    Default

    Quote Originally Posted by David_M View Post
    This might prove useful to some of you. I wrote this ROM originally to aid in repairing a TRS80 clone, but it works just as well in a TRS80.
    Just burn the ROM image into a 2732 eprom and put in socket z33. It does not require working RAM, although faulty video RAM does make the results less readable

    Untitled-2.jpg

    Rom image
    https://drive.google.com/open?id=1M6...-88_ZlzZyyDvCh
    David,

    I promise to give your ROM a real workout and, if you come up with something that will test the keyboard and E/I, put me down for one.
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