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…

As a recap, I’ve got a runnable system. Programs can be entered into the systems memory in hex using the keypad and display then executed. However, as it stands there are no additional input or output devices; only the keypad and the LED display and it’s all a bit limiting really. It’s possible to separate…

In the first exciting part of this series we got to the point of a completed design for the CPU board. By this point I’d got a PCB and working system. I realise that I have skipped two topics that need to addressed now. The keypad/display, and an interim solution to the INS8514 I/O device.…

Replicating the CPU board The first problem was to get hold of a schematic and make sure it was correct. On-line I found hi-resolution pictures of both sides of the two PCBs so printed them out, stuck them together and traced each track on the PCBs, comparing it with the schematic and there were a…