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…

Here you will find all the construction details for each of the boards in this project which I will actively maintain to include the latest revision of boards and documentation. I’m not going to hand-hold you though the construction of these boards. They have PCB foils and most have schematics. It’s pretty much up to…

In this thrilling instalment we shall look at the 8 bit LED display card. This card is probably the simplest expansion card there is. It contains eight LEDs, and you can display any value from $00 to $FF by writing to a specified address. The address is specified on the card. The initial version of…