6502 cycles and subtleties (was Re: Assembly on a Apple IIc+)

From: Eric Smith <eric_at_brouhaha.com>
Date: Sun Feb 9 01:04:22 2003

ben franchuk wrote:
> A hidden gotya is the index registers are 8 bits. No problem
> for small dedicated control but somthing that limited high
> level languages to Basic and Pascal p-code.

I'd have to disagree. There were plenty of other HLLs available
for the 6502. The 8-bit index register isn't an issue using
the indirect indexed addressing mode, e.g., "LDA (FOO),Y", in
which any pair of consecutive zero page locations can act as a
16-bit base, with the index register as an offset.

The biggest limitation for HLL support was the 256-byte stack
limit; if you needed more stack you had to roll your own.

It was certainly not as nice as a 6809, but then it predated
the 6809 by several years.
Received on Sun Feb 09 2003 - 01:04:22 GMT