13 Mar
2003
13 Mar
'03
9:40 p.m.
Tony wrote:
Think of the 6507 as (very) programmable counter chain
(in the simplest
case just have it executing NOPs and JMPs).
Typically you want some instruction other than NOP. For instance,
using LDA immediate lets you fetch consecutive addresses on every
cycle.
I once had this idea (which I've never followed
up) to use a common,
fast, 8 bit processor with no instruction pipelining (so you know what
the buses are doing and when) as a microcode sequencer. Just give it 8+n
bit wide memory, with the 8 bits consisting of NOPs and (conditional)
jumps. the n bits are the control lines to whatever you're microcoding.
Back in 1993 or so, I was thinking about using an AMD 29005 RISC
microprocessor as a microprogram sequencer for a 36-bit computer.
But the 29005 doesn't qualify as common.