Retro Computing

PC6502 Progress

25 October 2025 /

In my previous blog entry I posted about the 6502 computer PCB I made, since then a lot of progress has been made. A lot.

Firstly the timing issue has been overcome, the 6502 will now happily run at 14MHz (tested up to 17MHz), the issue was that the way I had implemented the logic in the CPLD for the FT245 serial port was messed up. My partner, Jayne, helped with that and found the issue.

I’ve also added a whole bunch of different PCBs, so here’s a couple of pictures;

So bottom to top;

  • Power supply PCB – This gives me up to 15W from USB-PD or if you used an external 9V-36V DC power supply you can have up to 50W (more on why later)
  • The 6502 CPU Card – The 6502 (currently running at 10MHz), ROM, RAM and USB C serial port for console
  • The FM Speec card – The has an OPL3 FM engine on board (YMF262) and an allophone speech synth chip (SP0256-AL2).
  • The Storage card – this gives 8 bit access to Compact flash cards
  • Dual SPI card – this is taken from Dayrl’s 65SPI2 project All I’ve done is pop two of these on the PCB and add some address decoding.
  • 65C22 VIA card – a simple 65C22 based VIA card, allowing 2 ports of 8 bit input or output (or any mix).
  • Apple II slot card – This provides two apple II style slots (but not all of the power rails, and a different address)
  • In the top is a a T2A2 transputer adapter card fro, Geekdot.com and this is why having higher power is essential. Each TRAM (Transputer module) needs about 800mA, I plan to have 4 TRAMs.

Aside from the Apple II slot everything is working a treat.

Here is a demo of the allophone and FM card (it took me ages to get a single tone from the FM engine);

Next steps with this are, a keyboard and keyboard interface (not PS/2). And a small display so that I can put graphics on.

Then there is a lot of software that needs writing, saving and loading to the CF card (currently raw data block read/write work), input from the keyboard and of course output to the display.

I am saving space in my memory map for a VideoBeast from Feersom which should make this quite a complete system. Then it’s just writing some apps for it, things to do raytracing, mandlebrot and maybe a few simple games too.

I update my github with progress as things move forward – https://github.com/TechPaula/PC6502/

Most of all this has been a really fun project and nice break from synthesizers. A bit like a holiday.

electronics and synth nerd.