The Gameboy CPU is signifigantly less capable than a full z80. It's missing key features like the IX and IY registers (and thus addressing modes), most of the 1

The Gameboy CPU is signifigantly less capable than a full z80. It's missing key features like the IX and IY registers (and thus addressing modes), most of the 16-bit ALU, the second set of "shadow" registers intended for interrupt handling (instead, almost all gameboy interrupt routines start by pushing all the current registers onto the stack), and a bunch of other things I forget. There's also some stuff it adds, such as the swap instruction (swapping the upper and lower nibbles of a byte) and the stop instruction (puts the gameboy into a low-power state until it is woken by a keypress).