The Z80 Instruction Exerciser executes every opcode and then compares checksums of memory to checksums generated on actual hardware. As in the last project, writing unit tests along the way was integral to success.Īlso like last time, I was able to verify my Z80 implementation by using a diagnostics program written for the original CPU. This part of the project took the longest I had to rework all the code that set the flags register. This StackOverflow post was a great starting point for identifying the differences between the 8080 and Z80. I hadn't implemented the auxiliary carry flag and a few other opcodes that Space Invaders didn't use. Also, the 2016 version of the Z80 CPU User Manual provided a lot of details.Īfter implementing the additional instructions, it was time to go back and fix areas of the code that I hadn't completely finished for Space Invaders. This site offers an interactive and searchable list of opcodes, which was extremely useful. I then got to work implementing the additional instructions present in the Z80. I started with a copy of my Space Invaders repository and began stripping out the Space Invaders-specific code. Pac-Man boards are just Pac-Man boards with a daughterboard installed to modify the original CPU behavior and swap/patch certain ROMs.

An additional bonus was that with minor changes, I would also be able to emulate Ms. This was great news if I built a Z80 emulation core, I could then reuse it for other projects! I decided to start with something simple and well documented: Pac-Man. Arcades: Pac-Man, Rally X, Dig Dug, Galaga.Handhelds: Nintendo Gameboy, Sega GameGear.Home computers: ZX Spectrum, TRS-80, MSX, Amstrad CPC.I looked around for other systems that used the Z80, and there is no shortage! If I chose to emulate a Z80-based system, I would be able to reuse a large amount of my 8080 core's code. I knew that the Zilog Z80 CPU was a 'cousin' to the 8080 it was largely backwards compatible with the 8080, but also contained a superset of instructions. Once I finished up my Intel 8080 CPU core for my Space Invaders emulator, I wanted to move onto something a bit more challenging.

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