The ASCII [[R800]] that powers the MSX TurboR is a seriously beefed up version of the Z80:
* The ALU of the R800 is 16-bit instead of 4-bit for the Z80. This change allows instructions that were being executed in 4 clocks cycles to be done in 1 clockcycle.
* The instruction set of the R800 is almost identical to the Z80. Only 2 instructions have been added: MULUB and MULUW. And many of the undocumented instructions of the Z80 were made official.