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Thread: Porting CP/M-68K to a recycled board

  1. #1
    Join Date
    Aug 2017
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    New Mexico, USA
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    Default Porting CP/M-68K to a recycled board

    A decade ago I purchased a box of salvaged single board computers based on Motorola MC68302. They were made by ADC Communication as a controller for their Soneplex communication product line. I'd had no documentations but I figured out how to turn on the power and observed the outputs of console serial port to know these are likely good working boards.

    I tried a couple times to upload my own 68000 executable files, but were not successful. Eventually I wrote a boot monitor, took over the boot flash and overwrote the existing software. In the process I also figured out most of the pc board wiring. Recently I have sufficient understanding of the board to port CP/M 68K to it.

    The board has 3 banks of flash memories. The first bank is 256K bytes and hold the monitor. The other two banks are 1 megabytes each. Collectively they formed a read-only disk to hold the CP/M 68K ver 1.3 distribution files. The RAM is 1 megabyte with the top 256K backed up with a super capacitor. The backed up RAM may serve as a small RAM disk. CP/M 68k resides in $15000 - $1FFFF and the Transient Program Area is from $20000 to BFFFF, or 640K--which "ought to be enough for anybody". I copied the CP/M distribution files into flash and configured the BIOS for Flash disk and RAM disk and this is what I have:
    Attached Images Attached Images

  2. #2
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    Attached are schematics of the pc board. It took quite an effort to trace through the pc board because it is a 6-layer board with power/ground layers in the center. Fortunately the inner signal layers are clearly visible so when all components are removed, circuitry can be traced visually. To speed up the process, I took high-resolution pictures of component side and solder side and overlay them in Photoshop so I can follow signal traces between component side and solder side easily. In many instances it is still necessary to use cotinuity meter to verify the connections.

    Schematics were drawn using a 20-year old WINDRAFT by IVEX. Now that's vintage software!
    Attached Files Attached Files

  3. #3
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    Aug 2017
    Location
    New Mexico, USA
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    A CompactFlash daughterboard is added to the DIN41612 connector to make the system more usable.
    DSC_30901016.jpg

    I documented my efforts in repurposing the SPX-MPU board here:
    https://www.retrobrewcomputers.org/d...:lasmo:spx-mpu

    The process to convert it to run CP/M-68K is here:
    https://www.retrobrewcomputers.org/d...rds:sbc:mpu302

  4. #4

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    This is pretty neat.

  5. #5
    Join Date
    Aug 2017
    Location
    New Mexico, USA
    Posts
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    Thank you. I have 6 of them for sale at RetroBrew. They are $30 per set (MPU board, daughter board, including the CF drive)

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