Building a computer around a classic microprocessor is something of a rite of passage for aficionados of vintage computers. But for those that have never built their own computer, the task can seem very daunting. Using an existing design can be a great way to get started with your own build.
Matt Sarnoff has recently completed a minimalistic single-board computer he calls the 68k nano. It is a simple, easy to understand design that can be built on a PCB with the available design files, or even on a breadboard.
Based on the Motorola 68000 microprocessor, the 68k nano uses a handful of through-hole components that will keep the retrocomputing purists happy, while also sneaking in some more modern conveniences like a CompactFlash card reader. The 68000 runs at 12MHz and offers 1MB of RAM and 64KB of ROM storage.
Only two 7400-series glue logic chips are required, keeping the design as minimal as reasonably possible. This simplicity does have some drawbacks, especially when considering address decoding. Several address blocks are inaccessible to avoid bus contention issues.
Communication with the computer is accomplished via a 16550 UART chip. This interface can be accessed via Python 3 with the PySerial library to upload programs. Sarnoff has also provided a ROM image that supports loading programs from a CompactFlash card, and also offers some basic debugging functionality that can be accessed with a set of simple commands.
Sarnoff has no plans to further develop the 68k nano at this time, but there is plenty of opportunity for others to add additional functionality. It provides an excellent, easy to understand platform to jumpstart the development of a new retro-style computer.