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Thread: Mostek Z80 CP/M Computer System from 1979

  1. #11

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    Quote Originally Posted by Dwight Elvey View Post
    Mike is great with things you'd just never expect. If you have some 2716s, it is simple to make the adapters. I usually stack two machine pin sockets under a 2716. If you take a small piece of wood with a hole in it is easy to pop the machine pins out where you don't want to make connections. The pins pop out the top. On the top socket I run the extra wires for the 2716. I use 30ga wire and after making the connections, I trim the excess pins on the ones to not connect, just in case.
    As for cables, I believe the boards bring the signals to the back connectors as well so that such connections are out of the way.
    For most things, the scope you have sounds like it is enough. Being able to program 2716s will make trouble shooting much easier. You should be able to write simple targeted loops to test the different parts of the system. Use the spec sheets for the parts. If you don't follow what is needed, let us know. A handy trick when writing small test programs is to use an I/O address that you've proved to be working. You can then use that address to sync the scope by putting the one channel on the select lead for that I/O. If it is an output, you can also read and data information, either from the device or just scope the data bus pins. Don't make the program too complicated.
    The first thing to check is the RAM. It looks like you have DRAM but I can't see the numbers on them. Your init needs to turn on the Z80 refresh ( look at the spec sheet ), if they are DRAM. Make simple test. Just writing and reading 55 and AA will find most RAM failures.
    Dwight
    Im sorry, i totally overread your message.
    Yeah, i have a bunch of 2716's, and i planned to make adapters anyways. Altough i dont quite gt what you mean by stacking amchine sockets and then pop them out with a piece of wood... i planned to use one normal socket and on th bottom one i use a socket that has pins on both sides, solder them together, and at points where its not needed ill just wire them to the correct pins.
    That kind of troublshooting sounds pretty complicated, ill have to see how far i can get with it.
    The RAM chips are MK4116 Ram chips, i luckily have a bunch of them left in the case that some are bad, but i think it could get pretty complicated to programm something for this computer to check the ram, i just hope they are all good.

  2. #12

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    You don't have to be tricky with the code. Just simple loops of repeated writes or reads.
    As for sockets, I mean what are called machine pin sockets. These are usually more expensive sockets and often variations used for wire wrap sockets. The individual pins are pressed into the plastic socket frame. You can align the socket upside down with the pin over the hole. I use short needle nose pliers to push the pin straight down. The hole makes a place for the pin to go as it pops out.
    Here is a pointer to the type I use:
    https://www.jameco.com/z/6100-24-24-...SABEgIkivD_BwE
    The code doesn't have to be complicated. It typically doesn't have more than 20 instructions at most. Remember, we are not writing a full diagnostic with user interface. It is just a short piece of code that will do something really simple to the piece we are targeting to test. I usually don't even bother to dig up an assembler program and just hand assemble the needed code. We just want something we can sync to a scope to look at the data or address lines.
    Dwight

  3. #13

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    Of course, do a pin check on the CPU. Look for voltages and signals, first. You need reset, clocks some data and address activity. It may not have all the bits but you want to see something happening on most pins. Look at the interrupt pins as well. A constant interrupt can be a problem. If you need to trace a signal, use a sponge wrapped in aluminum foil and an ohm meter( different sized pieces of sponge to do finer searches ). You can narrow down things a lot faster that way.
    Dwight

  4. #14

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    I thought I might write a typical program to show you what I mean. This is to find a handy I/O address to use for synching and possible status. Find some I/O device you will use and find the enable pin for that device. Places to look are serial chips, 8255s and such. You put one of your scope leads on the enable to sync to. With the other lead, you look at the address lines to see the next port address used ( subtract 1 ). You can use this address for all kinds of things. For status reports, choose one you are not testing. You can also use this program to determine the address(s) used by an I/O you will later write test programs for.

    Code:
    0000  01 00 00   LD BC, 0000
    0003  ED 41      OUT (C),B
    0005  0C         INC C
    0006  C3 03 00   JMP 0003


    Dwight
    Last edited by Dwight Elvey; May 13th, 2019 at 11:52 AM.

  5. #15

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    I'm not sure how your VDI board, the serial port on your CPU board, and your rear panel are wired, but you can probably figure it out with a few experiments. Or I can look at manuals tonite and try to figure out which serial port (CPU board or VDI) is jumpered to match the port number used for the console port in the monitor PROM.
    thre are tow connectors on the back, the bottom one is a simple backplane that connects very connecter together and provides power, and the upper connector has individual wires going to the io ports.
    It would be awesome if you look at the manual. you said you got a good hundred of them, could you maybe copy some of them that have schematics inisde and information about the AIM-80F or SYS-80F? I know thats exhausting to scan a whole book, but it would be really nice if you have th time for it.

    1) Connect the keyboard to the VDI Serial Port
    [. . . ]
    However, I imagine your system has been configured to use the video board, monitor, and keyboard.
    I tried that, no success. i also tried to hook the serial terminal port to my computer and use a serial terminal programm, but after sending a bunch of new line commands(/r+/n & /r & /n), but no success either.
    I looked at the wiring of the VDI serial Terminal connector, but its wired up very weirdly. Only the pins 10, 16, 17, 24 are connected, so no TxD or RxD.

    You don't have to be tricky with the code. Just simple loops of repeated writes or reads.
    I have really no experience with assembly, i have no idea how to code that. in the next days ill read myself more into it, maybe im able to write such a instruction.

    Now i understand how you make the sockets, although ill do it different

    Of course, do a pin check on the CPU. Look for voltages and signals, first. [. . .] You can narrow down things a lot faster that way.
    I already measured a bit, there is a good clock signal and some activity on all adress and data lines. i can provide pictures in the next days of the signals.

  6. #16

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    I have the magical ability to post replies just while a new one appeared...

    Its a clever idea, i just have to find a io device, there are several Z80 PIO chips.
    so that programm will scan for IO devices and does... what exactly? how can i see that it found one?
    I have to go for today, ill reply tomorrow.

  7. #17
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    Quote Originally Posted by Dwight Elvey
    ....You can align the socket upside down with the pin over the hole.
    I use short needle nose pliers to push the pin straight down.
    . ..
    Would you please show some photos of your design Dwight....


    Quote Originally Posted by Dwight Elvey
    If you need to trace a signal, use a sponge wrapped in aluminum foil and
    an ohm meter( different sized pieces of sponge to do finer searches ). ..
    You got me there Dwight......I have no idea what "sponge in foil" you are talking about;
    Would you please show some photos of your devices etc.


    ziloo

  8. #18

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    Quote Originally Posted by ziloo View Post
    Would you please show some photos of your design Dwight....




    You got me there Dwight......I have no idea what "sponge in foil" you are talking about;
    Would you please show some photos of your devices etc.


    ziloo
    I'll make some pictures of the adapter. I won't waste time wrapping a sponge in aluminum foil so you can see what a sponge looks like wrapped in aluminum foil. I'm sure you can imaging it is not all that complicated. The way it works is you put one ohm meter lead on the pin you wish to trace. The other lead you attach to the foil. You push the foil and sponge on the back of the board. If you get "0" ohms, you know the trace is someplace under the foil. Using a smaller piece of sponge, you can then trace it to a smaller area. Eventually the foil gets too many holes or tears. You simply replace the foil and you should be able to reuse the sponge.
    Dwight

  9. #19
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    Now you are talking Dwight!!!!

    You have many very clever ideas about troubleshooting,
    and one of these days you have to make it into a series of
    youtube videos that will immortalize you.

    Thank you very much for your response.


    ziloo

  10. #20

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    The foil and sponge idea is not mine, one of the others on this BB mentioned it. It is a lot faster than going one lead at a time.
    Dwight

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