The-8-bit-SAP-3 VS 8-bit-CPU

Well thanks, the .pdf I made can be found here: https://github.com/rolf-electronics/The-8-bit-SAP-3.

https://github.com/rolf-electronics/The-8-bit-SAP-3 , see page 17

I designed and built this: https://github.com/rolf-electronics/The-8-bit-SAP-3

I later built a version that can read/store a full byte (2 key-presses) and present it to a CPU.

My code is available here, it has evolved since then and I actually abandoned the in-Arduino emulator later (re-wrote that part in Verilog). So it is best viewed at historical tag "emulator_1.0" in the repository.

Mark your data using PROGMEM directive (see example).

My project sources are on GitHub. Theres a lot going on, and it is probably a bit over-engineered. You can start by taking a look at Arduino sketch and client library.

I wrote an emulator for mine, then extended it to test out different designs, before building on hardware. The approach was a bit different, as I started by implementing 74-series logic chips. Then "wired" them together into CPU modules. This way emulator becomes a testable representation of what's possible using logic chips.

I wrote an emulator for my CPU in Verilog. Actually, I made it to test out various aspects before building, real hardware has not yet cached up with it.

The source code was in Python. I was able to debug it using Arduino-based adapter and (by using some "magic") translate into machine code binary. Since then I've switched to CustomAsm for code compilation and have other means to debug (emulator and debugger tool).

If you looking for examples: here's how you create the array (code generated using xxd -i command), and here's how you use the array.

In the beginning of program (on EEPROM), there's a small piece of code that reads all 256 address locations and writes them back. In BOOT mode, this effectively copies contents from ROM into RAM.

Complicated? Perhaps, but do not underestimate the power of automated testing! When you can run a couple dozen tests in just few seconds, at any time, it really gives you confidence about the system. Obviously, one should spend time writing the tests, but it pays back rather quickly.