Designing a complete extensible computer

9 March 2021

The Planck 6502 backplane can make a great retro computer if you add in the basic necessary boards. For the simplest possible configuration however, you need at least three boards : the backplane itself, the CPU board (which also contains RAM and ROM) and a serial board for I/O.

Following a reddit discussion on the Planck 6502 intro post it occurred to me that it would not be more expensive to have a single slightly bigger board that would house the CPU, RAM, ROM and serial chips, while keeping all the expansion the the original Planck backplane has.

So I started drawing up a schematic and a board layout, and it turns out that all this can fit on a 100mmx150mm board, just 50mm wider than the original backplane. And while this is outside the “cheap PCB offer” of the likes of Jlcpcb, the price is still very reasonable. Actually it costs about the same as one backplane and 2 expansion boards.

So I feel that this new design is a win for most situations. I do not recommend you get it fabricated just yet since it has not been tested and will probably have a few bugs.

However, I cannot resist putting a 3D view here:

Planck computer 3D view

Hope you like it, contact me with any comments or suggestions.