Virtual vs Physical memory (was Re: Designing around a 6502 )

From: Roger Merchberger <>
Date: Wed Feb 12 15:42:00 2003

Rumor has it that Stuart Johnson may have mentioned these words:

> > > PS Is the 6809 a 8 or a 16 bit CPU?
> > Yes.
>:-) Good Answer

<AOLUSER> Me Too!!! ;-) </AOLUSER>

>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.

So where would that put the Hitachi 63C09? It's 6809 compatible, but in
6309 mode, it has 4 8-bit registers, combinable to 2 16-bit registers that
you can do full 16-bit arithmetic on... but wait! There's More! No, not
Ginsu Knives.....

All four registers can be combined for 32-bit math functions!

And even without using the added registers, in 6309-mode, 6809-programs run
15-20% faster on average, due to decreased clock cycle times on many

Too bad they're not still making 'em... :-( -- although I've always
wondered if their newer processors (like the SH-3<??> ) are based on it...


Roger "Merch" Merchberger -- sysadmin, Iceberg Computers
[1] "Makes a guy wanna say `Hot Diggity!`" -- Me
Received on Wed Feb 12 2003 - 15:42:00 GMT

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