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MOD68

Modular 16bit retro computers using cheap 4-layer 100x100mm PCBs

photondreamsphotondreams
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100x100mm 4 layer PCBs can be made cheaply with special offers from PCB houses.

Let's take advantage of that to experiment with a variety of interesting components for larger 68k projects.

So that we can also experiment with programmable logic, let's make the expansion connector compatible with the old Altera UP1/UP2 development kits, allowing us to interface with 5V FPGAs and CPLDs from the late 90s.
This platform is used by me to gain experience and insight into the workings of major components of my projected Amagaki computer. It is also a suitable platform for early system software development.

MOD68 currently supports remote debugging using GDB Remote Serial Protocol, including vscode integration.

  • Ready to begin OS development

    photondreams • 01/11/2026 at 17:43 • 0 comments

    MOD68 is alive and kicking and ready to start development on what will eventually morph into Amagaki OS once I figure out how all the new chips work and assemble the larger board.

    For now, on MOD68 we have :
    - A bootloader with interrupt-driven UART that accepts programs using XMODEM-1K (with CRC)
    - A loadable firmware updater that also accepts a new firmware image using XMODEM-1K and writes to flash
    - A GDB remote serial protocol handler active on UART channel B, with source-correlation, tracing and breakpoint support
    - Full integration of debugging in vscode
    - MOD68-LA, a logic analyzer interposer board that provides 64 signals to the logic analyzer while replicating the expansion connector. This lets me capture and view all bus activity in real time.
    - A 10ms system tick timer using the UART's timer
    - A 100 page draft of the OS design document

    Time to get coding!

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