The System 1 starts out as two euro cards stacked one on top of the other; CPU at the bottom with Keypad/Display on the top. It’s nice, compact and very pretty, but rather useless as soon as you want to start hooking it up to things. Quickly you realise that you are going to need…

During expansion card development, it’s handy to be able to poke around the card with an oscilloscope or multi-meter probe, but you can’t do that when the card is seated in it’s home position in the rack. The euro extender card plugs into the backplane slot, and then allows the expansion card to be plugged…

The Segment Address Decoder (SAD) The 6502 CPU has no special I/O instructions or hardware support signals; unlike the Z80 CPU for example, so for the most part any expansion boards need to occupy one or more addresses within the 64K memory map. In the 6502 world, hardware is usually classed as “memory mapped”. Whilst…

The keypad went though several design iterations before I got something I was pleased with. The initial PCB design was flawed in several areas and whilst it worked and was invaluable for getting the system running, longer term it needed to be updated. I decided not to include the cassette interface as I can’t imagine…