13 Feb
2003
13 Feb
'03
10:47 a.m.
[Charset iso-8859-1 unsupported, filtering to ASCII...]
----- Original Message -----
From: "Eric Smith" <eric(a)brouhaha.com>
To: <cctalk(a)classiccmp.org>
Sent: Wednesday, February 12, 2003 1:57 PM
Subject: Re: Virtual vs Physical memory (was Re: Designing around a 6502 )
:-) Good Answer
This has been argued many times. Personally, I would go with the width of
the accumulator(s), 8 bits for 6809, even though there are special (or
perhaps BECAUSE they are special) instructions that use the combination of
the two accumulators as one 16 bit ("D") register.
I tend to agree, but I would specialize that even further. As time goes on,
I become more convinced that ALU width should be the determinant of bittedness.
The 6809 requires multiple ALU passes for a 16 bit operation because the ALU
is 8 bits wide. The 68000 is a 16 bit processor for the same reason.
I seem to recall that that makes the 8080 a 4 bit CPU, though.
Eric
PS Is the
6809 a 8 or a 16 bit CPU?
Yes.