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Thread: Mostek Z80 CP/M Computer System from 1979

  1. #21
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    Quote Originally Posted by deramp5113 View Post
    Here's what I'd try first:

    1) Connect the keyboard to the VDI Serial Port
    Maybe the one marked VDI Keyboard instead in case the keyboard is a parallel scanned keyboard that might be harmed by RS-232 voltage levels?

  2. #22

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    Cruff - yes you are correct - I assumed a serial keyboard, and after looking at the posted pictures and digging into documents tonite, that assumption is wrong. So Maggi, ignore that post...

    Here’s what I’ve learned after more research tonite. The video board can be configured to look like an external serial terminal, or accessible on the bus by the Z80. Your video board is configured to look like an external serial terminal. If wired per the drawings, the VDI serial port on the rear of your computer is wired as DTE. The VDI keyboard port (now that I see it), attaches to the keyboard cable (of course).

    The “Serial Terminal” port is used by the CPU board and DDT-80 monitor as the console port. If wired per the drawings, this port is wired as DCE. So as Cruff suggested earlier, it looks like you connect your video board/terminal to the computer by connecting the VDI serial port to the “Serial Terminal” port. Since the VDI port is wired as DTE and the console port is wired as DCE, a straight through cable should work fine. Was there a short DB-25 to DB-25 cable already with your system by any chance?

    Looking at your keyboard, it looks like a capacitive Keytronix keyboard with the foam pads in each button. These are notorious for failing - often 100% - as they age. Most likely, all the foam pads will have to be replaced to restore operation of the keyboard. There are numerous threads about this topic. Even if you previously had all connections right, it’s quite possible the RETURN key on the keyboard doesn’t work and therefore the monitor never gets past the auto-baud step.

    As a temporary work-around, you can “type” directly on the pads of the keyboard PCB to bypass the foam pad problem, but for now, to eliminate several variables at once, I’d connect a working terminal or terminal emulator directly to the “Serial Terminal” port and get to the point where you can get the monitor prompt up. That will be the starting point for further progress.

    Mike

  3. #23

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    Quote Originally Posted by Maggi#9295 View Post
    One question - where did you found the schematics? i havent sen them on the page you meantioned, could you provide links for them?
    Unfortunately, the manuals arenít online - itís a collection of manuals I purchased on eBay a few years ago. The manuals are permanently bound, so copying is difficult. I can try to get you whatever you need from them.

    Mike

  4. #24

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    Here is my 2716 to 2708 adapter. Notice the two pins missing on the right socket. This is the bottom socket. Notice the wires on the left socket. The next picture shows the two stuck together with a 2516 on it.
    Dwight
    Attached Images Attached Images

  5. #25

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    Wow, this therad really exploded over night...
    Dwight, you are a real trubleshooting expert. The foil-in-a-sponge idea is very very clver, ill try that on traces i need to know where they lead.
    I now also understand what you mean with the sockets, clever idea too.

    Connect the keyboard to the VDI Serial Port
    Luckily i rad that wrong, i ahve not done that. the keyboard was always connected to the "VDI Keyboard" port, i also think its conected over a parralel siganal.

    Here’s what I’ve learned after more research tonite. [. . .] Was there a short DB-25 to DB-25 cable already with your system by any chance?
    thanks for doing this. yeah, i already assumed that the missing parts were used to use the board to directly communicate with the computer, and yeah, i hav a bunch of DB-25 cables (both serial and all wires just connected together for parralel use, ill use that one.)

    Looking at your keyboard, it looks like a capacitive Keytronix keyboard with the foam pads in each button. [. . .] therefore the monitor never gets past the auto-baud step.
    i alrady hoped that thats not the case, ill have to open the keyboard and see.

    As a temporary work-around, you can “type” directly on the pads of the keyboard PCB to bypass the foam pad problem, but for now, to eliminate several variables at once, I’d connect a working terminal or terminal emulator directly to the “Serial Terminal” port and get to the point where you can get the monitor prompt up. That will be the starting point for further progress.
    well, the problem is tht i already treid to hook it up to my computer (because i dont have a serial terminal or imilair things), but it didnt worked. (although i have no idea if the pc really sended signals, its complicated to measure with a oscilloscope, or i am just to dumb for it. has anyone an idea how to set up a oscilloscope so the screen only refreshes when it gets triggered?)

    Ill connect the VDI serial port to the Serial terminal port, and tear the keyboard apart, ill update you when i did that.

  6. #26

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    Guys! I did it(more like: the computer did it)!
    I connected the "VDI Serial Port" to the "Serial Terminal", and on bootup it wasnt showing anything, but after i pressed Enter the DSK ERR showed up and a dot in the next line.
    I just pressed random keys to test the keyboard, and the letters appeared on the screen. So i have a lot of luck that the keyboard is functioning.
    I dont want to put a disk in at this point, im scared that they might break, what do you think?
    (btw, if a moderator sees the post, what should be the case, why do m posts still have to be aproved by a moderator? how many do i have to post so thats not the case anymore?)

  7. #27
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    Quote Originally Posted by Dwight Elvey View Post
    Here is my 2716 to 2708 adapter. Notice the two pins missing on the right socket. This is the bottom socket. Notice the wires on the left socket.
    That is an elegant solution.

  8. #28
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    Quote Originally Posted by Maggi#9295 View Post
    Guys! I did it(more like: the computer did it)!
    I connected the "VDI Serial Port" to the "Serial Terminal", and on bootup it wasnt showing anything, but after i pressed Enter the DSK ERR showed up and a dot in the next line.
    Yay! Now you can get down to really testing it out.

    I dont want to put a disk in at this point, im scared that they might break, what do you think?
    You've already placed disks into the drives, so why not try one of those and not write or modify the disk until you can get them copied?

    how many do i have to post so thats not the case anymore?
    10?

  9. #29

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    Quote Originally Posted by Maggi#9295 View Post
    Guys! I did it(more like: the computer did it)!
    I connected the "VDI Serial Port" to the "Serial Terminal", and on bootup it wasnt showing anything, but after i pressed Enter the DSK ERR showed up and a dot in the next line.
    I just pressed random keys to test the keyboard, and the letters appeared on the screen. So i have a lot of luck that the keyboard is functioning.
    I dont want to put a disk in at this point, im scared that they might break, what do you think?
    (btw, if a moderator sees the post, what should be the case, why do m posts still have to be aproved by a moderator? how many do i have to post so thats not the case anymore?)
    That is great! Let's see how your PROMs are reading at the three bad locations while in the machine. At the dot prompt type the three commands "M" commands shown below and see how your dumps compare to my PROMs. The differences are (were):


    Address Mine Maggi
    E801 ED E5
    ECC0 FF 00
    EF10 FF 00


    .M E800 E80F
    E800 C9 ED 5B FE FF 1A FE 40 38 05 FE C0 DA E4 E8 E6

    .M ECC0 ECCF
    ECC0 FF CD A1 ED 30 08 FD 7E 03 E6 03 B9 28 0F CD 8C

    .M EF10 EF1F
    EF10 FF D3 E4 DB E3 F6 C0 D3 E3 01 E7 80 ED B3 01 E7


    Mike

  10. #30

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    Two of the PROM errors are in the disk driver part of the PROM that is called by FLP-80DOS and M/OS-80 for disk I/O. The error causes the command for the disk drive to be stored in the wrong location in memory, however, it does not appear that this error will actually cause a problem with disk driver function. I agree with Cruff - go ahead and try booting a few of the disks!

    Mike

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