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It's not really a Z80. This article talks about the differences: https://realboyemulator.wordpress.com/2013/01/01/the-nintendo-game-boy-1/ https://realboyemulat

by DanBC 7y ago

It's not really a Z80. This article talks about the differences: https://realboyemulator.wordpress.com/2013/01/01/the-nintendo-game-boy-1/ https://realboyemulator.wordpress.com/2013/01/01/the-nintend... Or this one: https://gbdev.gg8.se/wiki/articles/CPU_Comparision_with_Z80 https://gbdev.gg8.se/wiki/articles/CPU_Comparision_with_Z80

userbinator 7y ago
I suspect Nintendo may have started with a Z80 core and then customised it a little bit, similar to what they did with the almost-6502 in the NES.
- simias 7y ago
  It's definitely based on the Z80, but it's also different enough that you can't really base yourself on Z80 docs to implement the Game Boy CPU (I learned that the hard way). The flags are different, the timings are different, some instructions are removed, some instructions are added etc...
nottorp 7y ago
Ahaaa... I live and learn. About long dead CPUs.