Chuck Guzis wrote:
... And most professional apps for CP/M used the 8080
instruction
set initially--only later did a bunch of Z80-specific (e.g. ZCPR)
code come out. I never could understand this--in general, little to
be gained in speed by using Z80 codes.
I thought the main motivation was footprint, not speed. The relative
jumps save a byte each time they are used, and djnz saved two.
One of the most wasteful features in the 8080 instruction set, I
thought, were the 8 conditional calls and 8 conditional returns. I
would have much rather they had only unconditional call and
unconditional return only and used those 16 opcodes for something more
useful. Sure, they were useful once in a while, but not so often that
they should use up 6% of the single byte opcode space.