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Thread: Microkit 8/16

  1. #51
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    Yes, enabled is always on. It only goes off if you do RESET.

    I tried to get crafty and put the 1702 into my digital group machine, hoping it might spit out something useful out there.. unfortunately it just freezes the machine entirely with 'blocks'. Was worth a shot.

  2. #52
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    So the power-on reset is working.

    When you hit the RESET key after that, the CPU will be executing random rubbish in the RAM at that point.

    Just swapping boot ROMs (when the two machines are not physically the same) will just not work.

    Do you have any other machines that have IC sockets for 1702 EPROMs, but have a separate boot ROM or monitor that could be used to dump the ROM out?

    Just a thought...

    Dave

  3. #53
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    The only other machine I know has a 1702 is my OSI 500 board.. but I believe it uses those for boot as well.

    I'm very tempted to buy that solid state music 1702 board. But I think I will just sit down tonight and figure out how to wire a 'converter' to swap data lines as you suggested and we can dump the remainder the way we did previously.

  4. #54
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    Did you look at the pic I posted of that digital group proto board Dave? I'm trying frantically to find Marty's words on what it was but I could almost swear he said it has been set up for 1702 use.

  5. #55
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    I had quick look - but I wouldn't go plugging your one and only working ROM into something that may do damage to it if configured wrongly...

    The pinout for a 1702A can be found here http://www.tronola.com/html/1702a_prom_programmer.html.

    All you should need to do is to swap the pins 4-11 of the EPROM around with the socket pins. I will post a table tomorrow - it is getting a bit late now in the UK and I will make a mistake!

    Dave

  6. #56
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    Oh no. But what I will do is try tracing some telltale pins like voltage and see what is being put out. If I find a -9v pin that would be a telltale.

  7. #57
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    I am feeling pretty certain this board is wired for a 1702. Thankfully whoever did this used colored wires to make it easy to follow. Here's what I've traced:

    Pins 1,2,3 and pins 17-21 all have purple wires and go to pins 1-19 of a 74ALS541N.

    Pins 4-11 go to pins 2-9 of another 74ALS541N.

    That kind of matches the address and data out pins of a 1702.

    Pins 12, 13, 22 and 23 connect to VCC.

    Pins 24 and 16 are tied together and go to to one side of a large resistor and diode.

    Pin 14 is connected to pin 1 of a 74F04.

    I don't know.. I kinda feel like this is a 1702 reader or some kind. I don't know what the two white empty sockets do, or if the pins on the opposite side are just convenient tie-together points for the wiring. I'm not sure if this board was finished. But it definitely looks like it was set up for 1702s.

    I'm guessing the DIP switches select where in memory the ROM contents would go.

    The board is a officially called a 'DG-3002-A Memory w/w prototype' board, so it plugs into a RAM socket.
    Last edited by falter; December 14th, 2019 at 03:41 PM.

  8. #58
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    Sorry... my first line - all the purple wires from 1-3, and 17-21 of the ROM socket go to pins 11-19 of one 74ALS541N.

  9. #59
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    So, here is my suggestion for an EPROM adapter...

    Wire a socket (for the EPROM) to a header plug pin for pin EXCEPT for the following:

    EPROM pin 8 to header pin 10.
    EPROM pin 9 to header pin 11.
    EPROM pin 10 to header pin 8.
    EPROM pin 11 to header pin 9.

    This should keep the least significant 4 bits of the byte the same (so I can use them as check bits), and should swap over the top two bits of the data byte - so the character we get for each byte on the VDU display should now change.

    I should then be able to reassemble each byte, with four bits acting as check digits (i.e. they should be the same as last time)...

    Dave

  10. #60
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    Unfortunately, I think I have managed to disassemble as much as I can with 25% of the program missing! I just seem to have too many variables to make any further inroads. After a good nights sleep I may have some more ideas of course, but it would be much, much easier to have the remaining two bits of each byte to fill in the puzzle rather than guessing!

    Dave

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