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Thread: Mostek Z80 CP/M Computer System from 1979

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  1. #1

    Default Mostek Z80 CP/M Computer System from 1979

    Hello everyone,

    I recetly got aware of a very old (and very rare?) Mostek Computer (from what I could find out its called SYS-80FT), featuring:
    - a MK3880 Processor @4.916
    - 4x 2708 EPROMs
    - 8x(+24x on RAM Expansion Board) MK4116 DRAMs
    - 2x 8" Single Sided Floppy Drives
    - several Serial/Parralel Interfaces
    - a Video Interface Adapter for Keyboard Input and Vido Output

    I found the Computer stored away in a shelf at a Universit, probably last "used" 1998, someone tried to boot it up but wasnt sucesfull at that and wrote "Scrap" on its side. There was absolutley no documentation left about the Computer, and it probably has been tossed out while the University scraped like 90% of its inventory in order to make space. Luckily the Screen, the Keyboard and a PROM-prgrammer, as well as a bunch of Floppys were still there. They (hopefully still) contain Operating systems (CP/M, FLP-80DOS, MOS 80) and Programs(A Chess Game, BASCOM-80 & Several other disks).
    When i Power up the Computer the (very loud and very big) fan and the floppy drives spin up, the keyboard makes a very short beep-tone and a blinking cursor is visible on screen. Thats it. The floppy-drives dont seem to get activated at all, not even when a disk is inserted before or after "booting".

    I already did a bit of measuring, the voltages are all only a maximum of 0,5V off, and the data pins on the floppy controller dont seem to change. The EPROMs and some bus-driver-chips get pretty warm, but main chips lik th CPU, the floppy controller itself and RAM chips dont seem to gain any temperature. I feel pretty lost with this thing, i dont have a Idea how i could troubleshoot this Computer, i would really appreciate your help.

    Some Pictures of the System:
    IMG_2202.jpgIMG_1761.jpgIMG_1762.jpgIMG_1804.jpgIMG_1801.jpgIMG_1772.jpgIMG_1777.jpgIMG_1766.jpgIMG_1764.jpgIMG_1831.jpgIMG_1881.jpgIMG_2159.jpg

    Here is some information about my computer and some files i found in the web that have some information about it:
    -Information about some boards installed: https://usermanual.wiki/Document/197...313031759/view Page 622-639
    -Information about individual boards, the whole System and some Software: http://the-eye.eu/public/Books/Elect...k1979_text.pdf Page 59-134
    -Information about some boards: http://www.bitsavers.org/components/..._Data_Book.pdf Page 362-397
    -Pictures and ROM contents (go to pictures/downsized/ for viewig pics): https://github.com/Maggi9295/Mostek-Z80-Computer
    -Video of the Computer "Booting": https://www.youtube.com/watch?v=bJr7...&index=2&t=66s

    I would really like to get this Computer back to run, so i appreciate every piece of help, and if its already that you read this very long post.
    Kind Regards, Maggi

  2. #2
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    Does it actually have the serial I/O controller board? It looks like two of the DB-25 connectors might be wired for RS-232 serial. If you attach something to them, is anything output on the serial ports at power on?

  3. #3

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    Do you have access to an oscilloscope or a logic analyzer? Also, you may want to disassemble the ROMs. These development systems are cool but often the documents are lost to the wind. There is likely some single point failure that has stopped the entire thing.
    You can make a switch type CPU emulator to do static test but you won't be able to run any DRAM ( I'm not sure what the RAM was. Pictures are too small. ).
    What programming skills do you have?
    Have you worked with any of the Arduino stuff?
    Do you have access to a programmer that can program 2716's ( easier to deal with and get than 2708's )?
    Dwight

  4. #4

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    Thanks a lot for your answers,

    Does it actually have the serial I/O controller board? It looks like two of the DB-25 connectors might be wired for RS-232 serial. If you attach something to them, is anything output on the serial ports at power on?
    The Ports you mean are probably the two top ports, they are connected to a handmade Circuitboard on the inside that was used by the University for some other hardware stuff, but i dont plan to leave this board in there. afaik th board is controlled by software, and as long as its not booting any software it doesnt output anything.
    There are two other serial ports, the one is the "VDI Serial Port" a serial port controlled by the Video Interface Controller. The other one is a "Serial Terminal" connection, that sounds very hopefull. i connected them correctly to my pc and also hooked them up to a oscilloscope, but no signal, only a continious high signal.

    Do you have access to an oscilloscope or a logic analyzer?
    I "only" hav a two channels analog/digital oscilloscope, i can connect it over RS232 to my computer.

    Also, you may want to disassemble the ROMs.
    I tried to with several programms, but had no "really" nice dissasembly. An online disassembler dissasembled it well, but had no other functions and just listed the instructions one after another.
    Then i found Ghidra, probably a very good programm, but it only dissasebles a very first bit of the code and then gives some error messages, like "cant accsess adress something", i have to play around with that one more.

    There is likely some single point failure that has stopped the entire thing.
    Yeah, i have the same feeling, but finding it will b the problem.

    What programming skills do you have?
    Its decent, i programmed a bit with everything, but probably forgot most of it again(i could re-learn it if neccesary)

    Have you worked with any of the Arduino stuff?
    Yeah, i did a lot with it one or two years ago, i have some basic equipment and homemeade expansions laying around.

    Do you have access to a programmer that can program 2716's ( easier to deal with and get than 2708's )?
    I have a Batronix Batego II, but it cant ahndle the 2708 because it needs three voltages and a programming volatge. it can do the very similair(especially in programming, because its very special with theese chips) TMS2716, i planned to make an adapter to read and programm 2708's, i already did a prototype reader from connecting a breadboard with wires to the programming socket to and using external voltages to read the EPROMs.

  5. #5

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    This computer contains some of the exact same boards, PROMs and software as in the Mostek AID-80F. See http://deramp.com/mostek.html and especially the restoration document referenced there.

    Two completely different bus connectors, and therefore, board layouts are used between the AID 80F and your machine, but the schematics for the boards are essentially identical other than connector PIN numbers. I used the manuals I found for your versions of the boards to figure out how my boards worked. The new variable in your system is the video board and keyboard - I don’t have that. Mine uses a serial port console.

    Let me dig through the manuals I have and see what I can find for you. I’ll also check and see if your PROMs are the same as mine. The PROMs were originally designed for a FLP-80DOS system, which was later replaced by a much more powerful CP/M clone called M/OS-80. M/OS-80 was based heavily on CDOS, Cromemco's CP/M clone. I have ported CP/M 2.2 to the machine, but CP/M was not on any of the disks that came with my machine.

    With a serial port console, no disk activity takes place until you press return on the keyboard (the PROM waits to autobaud). If your keyboard and video board are treated like a serial terminal by the system (like MITS did with their video board for,the Altair), then maybe your computer is also waiting for return to be pressed before it attempts to boot the disks.

    Mike

  6. #6

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    I've done a little digging. Your PROMs match mine except for three locations. The mismatches do not appear to be intentional. However, the failure is bits reading zero instead of one. Bit rot is usually the other way around.

    If your hardware is functional, I believe we can get your system up and running. You mention you have FLP-80 disks, M/OS-80 disks, and CP/M disks. I also have M/OS-80 disks, and as I mentioned, I wrote my own CP/M for the machine, but I have no FLP-80 disks. I have utilities for archiving and restoring floppy disks to/from a PC through the serial port, so I'm excited we can archive your FLP-80 disks and then try them on my machine. I'd also like to archive the CP/M disks you mentioned.

    It appears your video board is actually just an external serial terminal, however, the video board for the terminal happens to be housed inside the main computer chassis and uses the bus connector only to obtain power. So technically, your console is just a serial terminal like with my AID-80F machine.

    The red toggle switch on the CPU board is used to determine the auto-start address. In one position, the CPU jumps to zero on reset. In the opposite position, the CPU jumps to E000 on reset (the EPROMs). You want the switch setting that jumps to E000. Unfortunately, it doesn't appear that your board has the switch labeled (mine has a "0" on one side and an "E" on the other side).

    Here's what I recommend to try booting again.

    1) Never have the disks inserted when you power up the machine or turn it off. It's not unusual to clobber a disk during power on/off.
    2) Set the red toggle switch in the up position - towards the reset push-button. That's the E000 position on my board.
    3) Turn on the computer
    4) Insert a boot disk into the right drive (just a guess for now that it is drive 0)
    5) Press the reset button
    6) Press RETURN on the keyboard (may take two presses, but usually one does it)
    7) You should see one of the drive lights come on as it tries to boot.

    You can boot directly into the DDT-80 monitor in PROM by following the boot procedure above but do NOT install a disk into the boot drive. After reset, press RETURN as always, you'll now seek "DSK ERR" and get the "." prompt of DDT-80. There are some notes about DDT-80 in the M/OS-80 manual: http://deramp.com/downloads/mostek/A...s%20Manual.pdf

    Mike

  7. #7
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    Quote Originally Posted by deramp5113 View Post
    It appears your video board is actually just an external serial terminal, however, the video board for the terminal happens to be housed inside the main computer chassis and uses the bus connector only to obtain power. So technically, your console is just a serial terminal like with my AID-80F machine.
    Does it require an external cable to make the connection between the connector marked "Serial Terminal" to the "VDI Serial Port" to function?

  8. #8

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    Quote Originally Posted by Maggi#9295 View Post
    I recently got aware of a very old (and very rare?) Mostek Computer (from what I could find out its called SYS-80FT), featuring:
    I see you referred to the system as a "SYS-80FT." When I wrote a CP/M BIOS to support my AID-80F, it looks like I had also determined it would run on the SYS-80FT. Here is a part of the source file header in my BIOS:


    ;************************************************* ***************************
    ;
    ; CP/M 2.2 BIOS for Mostek Development System computers. This
    ; includes the AID-80F and SYS-80FT systems. The primary criteria
    ; is presence of the SDB-80 (or SDB-80E) CPU board and the FLP-80
    ; (or FLP-80E) floppy controller board. The monitor PROMs on the
    ; SDB-80 CPU board provide disk I/O support routines that are
    ; called by this BIOS to do disk I/O.
    ;


    Mike

  9. #9

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    Mike has you on the right track. Make sure to set the write protect the right way on the disk. Very few failures will cause the drive to ignore the write protect. It is a hardware function of the drive.
    Dwight

  10. #10

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    I have checked the ROM locations you meantioned, and they are the same as yours. while that i found out, thatsome keys dont work at all, some need several hits until they appear on the screen(i might have to replace the foam pads inside anyways).
    here is a pic of the screen of the memory locations: IMG_2387.jpg
    I also inserted some diks, the CP/M disk seems to boot just fine, but i cant type anything in. always when i hit a key the disk seems to get loaded again and the CP/M prompt appears again, is there a special way you type something in CP/M?
    IMG_2393.jpg
    the MOS 80 disk gave me the following error:
    IMG_2394.jpg
    and another disk labeled with "BASIC Games & Sargon Chess" gave me a FLP-80DOS prompt...
    IMG_2397.jpg

    Yeah, as far as i know its called SYS-80FT(its mentioned in some of the databooks and on some floppys). Te hardware mentioned in your file header is also th hardware in my computer.
    So, as mentioned, i have no idea how to type anything in CP/M, and its even more complicated when the "R" key is one of the ones that dont work, so no "dir" commnd for now i guess...
    oh, and i checked again, yeah, 10 posts. im silly tht i havent looked that up before...

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