> I still don't understand the AND/OR values for reading joystick status
from
> the Portar documentation ?!?!???!?!??? ? ?!?!?!? ?!??!?!?:
>
> This rotine will read joystick 1 or 2:
> F3 di
> 3E 0F ld a,0fh Write this for Write this for
> D3 A0 out (0a0h),a Joystick port 1: Joystick port 2:
> DB A2 in a,(0a2h)
> E6 DF / E6 AF and 11011111b; 0DFh and 10101111b; 0AFh
> F6 4C / F6 03 or 01001100b; 04Ch or 00000011b; 003h
> D3 A1 out (0a1h),a
> 3E 0E ld a,0eh
> D3 A0 out (0a0h),a
> DB A2 in a,(0a2h)
Well, I'll explain. If you want to set-reset certain bits then you can use
the SET and RES-instructions.
But if you want to (re)set multiple bits, then those are very slow. In that
case it's easier to use AND and OR.
AND %11011111 resets bit 5
OR %01001100 sets bits 6, 2 and 3
AND %10101111 resets bit 6 and 4
OR %00000011 sets bits 0 and 1.
If you check out some joystickport-docs (about PSG-registers 14-15) then you
will find that these indeed are the correct values which have to be written.
Didn't you know 'bout this use of OR and AND yet???
~Grauw
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