Date   : Thu, 06 Mar 2008 15:07:49 +0000
From   : adsb@... (Andrew Benham)
Subject: TUBE chip, accessing 'Parasite' side - 16Mhz 65C02S

David Warrington wrote:

> I think ANYONE still using a beeb today should just "drop in a 65C02" or 
> "65C02S" into their beeb to allow them to use BASIC4 and the "65Cxx" 
> mnemonics in assembler, e.g. PHX, PHY, STZ, etc.  This is a no brainer and a 
> 5 minute exercise.

Perhaps.  Except many years ago I wasted a lot of my time trying to
debug code I'd written using the VIA to do some timer-driven stuff on
the user port.  The VIA wasn't working like the manual said.
Eventually I had somebody else test it on their Beeb, and it worked
fine for them.  At this point I remembered I'd put a 65C02 in my Beeb -
so I replaced it with the original NMOS processor and my code worked
fine.
I think the timing on the Beeb is "close the the edge", and the CMOS
processor has slightly different timings.  I've never put a CMOS
processor in a model B since then.

[ Everything else on the Beeb worked just fine with the CMOS processor,
it was just programming the VIA that didn't work.  Perhaps on another
machine it would have been OK, or perhaps something else would have
failed ...]

-- 
Andrew Benham         adsb@...       
Southgate, London N14, United Kingdom

The gates in my computer are AND OR and NOT, not "Bill"