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

  1. #1

    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


    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


    A CompactFlash daughterboard is added to the DIN41612 connector to make the system more usable.

    I documented my efforts in repurposing the SPX-MPU board here:

    The process to convert it to run CP/M-68K is here:

  4. #4


    This is pretty neat.

  5. #5


    Thank you. I have 6 of them for sale at RetroBrew. They are $30 per set (MPU board, daughter board, including the CF drive)

  6. #6
    Join Date
    Oct 2014
    Pottstown, PA


    Remarkable. If I didn't have so many toys needing attention at the moment I'd check it out.

  7. #7


    I followed the link in your signature and really enjoyed your story about Kermit. I have no idea that Columbia University has played such a major role in development, porting and maintenance of Kermit.

    Kermit is THE file transfer tool between my PC and the repurposed CP/M 68K hardware. I use HyperTerminal on the PC with a transfer rate of 38400. I downloaded the Kermit for CP/M-68K (actual file name is gkermit) from Columbia U's website,
    it contains a precompiled gkermit.rel that works without recompiling (other than converting gkermit.rel to gkermit.68k for faster execution).

    Motivated by your experiences in recompiling Kermit, I take a closer look at the source codes. They are all in C, specifically the CP/M68K version of C, so they should compile correctly in the native CP/M68K environment without modifications. There are four C programs plus a header file:
    The submit file CGK.SUB is for compiling each C program. When that's done, LOGK.SUB is used to link them together. It takes about 4 minutes to compile and link on my repurposed hardware. The resulting gkermit works like the original. Very cool!

  8. #8


    This is how to "make a short story a lot longer"; I wrote down my experiences with recycling Soneplex MPU board at hackaday, and I'm not done yet.

    This is more than Vintage Computing; it is Salvaged Computing!

  9. #9
    Join Date
    Oct 2014
    Pottstown, PA


    Very nice follow up on the Kermit angle, thanks!
    Yes you are on to a subclass here of vintage.
    It takes a special type of mindset and tenacity to reverse engineer an old
    undocumented board and make it functional. Perhaps it will catch on!

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