Page 0 was Re: [Gllug] BBC and acorn bits

[Pete Ryland]

On 26/11/06, Andrew Black <andrew-li at black1.org.uk> wrote:
> Page 0 having registers looks like a recipe for registers accidently
> getting corrupted (eg a pointer set to 0 or a low value).
> I am most familiar with the VAX and Alpha architecture where the lowest
> page is always (at least under VMS) no access.  I have many times been
> saved by processes access violating rather than overwritting data and
> plowing on regardless.

IIRC, on the C64, page 0 was more like IO than registers.  Byte 0, of
all the things they could have put there, decided whether the IO
port's pins were read or write!  The IO port was of course only
present with the 6510, not the 6502.

Pete
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