I had some Z80 fun on a friends Sinclair - cant remember now if it was a ZX81 or a Spectrum (but what I do remember was it had seemingly very peculiar screen memory layout).
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(6502)Most programming in assembler required knowledge of what was free in page 0 - different for each machine.
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When writing assembler in any environment you need to know what memory is free, though true it was more important when dealing with the 6502's 128 16-bit registers
I think Tony may have hit on why I found the Z80 frustrating at the time (as I couldn't remember the details):
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Anyway, as for the Z80, one thing I hated about it was the indexed addressing modes. To me it was plain 'wrong' for the 8 bit 'offset' to be fixed (one of the instruction bytes) and the 16 bit 'base' to be in a register.
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For plotting things like sprites, I needed to index through a pixel mask table, the actual pixel table and arrange a plot offset (maybe with offset lookup from another table), that's three or four different indexes being managed at the same time. All hail the 6502
Of course that is a single specific use case. The Z80 was significantly quicker when I tried calculating Pi to an "unbelievable" several hundred decimal places !
TTFN,
Jon