[Coco] Extended basic 1.1 command?

camillus Blockx camillus.b.58 at gmail.com
Wed Nov 21 11:13:12 EST 2012


Hi guy's Sorry that I put my  big mouth in your conversation, but what you
do using the AND operation is NOT forcing the bits to zero, but more like a
mask out of that single bit you need. Masking out bits leaves the state of
the bits as they are in a read operation ( peek ) that is. Also on a write
( poke ) operation this will be the case and the most desirable one, if I
mat say so.

greetz cb


On Tue, Nov 20, 2012 at 8:05 PM, Harry Hurst <hhos at st-tel.net> wrote:

> > Oops, I get it now:  bit 7 is the joystick comparator bit and must be
> > forced to one;  bits 2-6 should already be ones if no keys are down.
> > Right?
> >
>
> Bits 2-7 don't matter in this case. They all have to be forced to either 0
> (AND 3) or 1 (OR &HFC) before you can determine the values on the button
> bits, 0 and 1. To do otherwise leaves too many possibilities open, and
> invites, if not disaster then at least a headache. If you wanted to also
> check some of the other bits you could PIA0= PEEK(&HFF00) and then BUT=
> PIA0 AND 3. Then the other bits are still there in PIA0 when you are done
> processing the buttons.
>
> HH
>
>
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