Re: Test: the cycle

["ict@ccess" <gids.rs@sasktel.net>]

On Feb 17, 2:36 am, Vladimir Ivanov <vlad...@XXXyahooXXX.com> wrote:
> On Thu, 16 Feb 2012, ict@ccess wrote:
> > On Feb 16, 7:29 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> >> If there's a one-instruction way, I'd like to know.
>
> > Have you tried
>
> > CLC
> > ROR $C036
>
> > the rest of the bits are not being used in $C036 and this has no
> > effect on non IIGS computers
>
> As I just mentioned, TSB/TRB for 65C02, 65802 and 65816.
>
> $C036 is full of other bits - there's the slot 4/5/6/7 disk-on control,
> there's the global shadowing bit, the ROM3 motherboard power-on bit, and
> even one reserved bit. Usually only slot 6 is set for compatibility and
> the bank shadowing is zero.
>
> Modifying with rotate seems catastrophical to me, even if it doesn't bite
> you at the instant.
>
> Also, ROR $C036 on non-IIgs computers will toggle the speaker few times.
> :-) Just as any other access to $C030 .. $C03F.

My Apple IIGS technical reference manual does not even list $C036, but
even if all these bits are used on startup as you say, then they can
be preserved since they don't have any immediate effect on any
hardware, other than possibly the shadow bit.  But I notice that
shadowing does not take effect until something is stored in shadowed
memory, but turning of shadowing of any screen, text or graphics, ,
then immediately back on should not show any effects on the screen.
To preserve the $C036 register without using the accumulator, you can
do it this way

CLC
ASL C036
ROR C036