[Coco] Re: Technical: PIA Help

Brad Grier bradgrier at cox.net
Fri Dec 2 18:37:14 EST 2005

Hmm. The coco 3 screen shot of the game at 
http://nitros9.stg.net/tetris.html shows keyboard help. Those keys work 
as described in David Keil's emulator.

Robert Gault wrote:
> Right, see it. My guess is that this is a routine to read both the right 
> and left joystick #1 switches. Setting $FF02 to $FF will block all the 
> keyboard entries, but the joystick switches should still get through and 
> be reported at $FF00. Bits 0-1 are right left switch #1 and bits 2-3 are 
> right left switch #2.
>     lda #$ff
>     sta $FF02
>     lda $FF00
>     eora #3
>     anda #3
>     sta <$0f
> Guess we need someone who owns the program to read the instructions and 
> indicate how the joysticks are to be used or if they can be used.
> Brad Grier wrote:
>> Correction: the interrupt start address is $c4e2, not $c4fe - I have a 
>> lot of numbers scribbled on the paper in front of me.
>> Brad Grier wrote:
>>> Hi Robert,
>>> I reached my conclusions by stepping through Mocha in debug mode. I 
>>> also used the debugger in Jeff Vavasour's emulator (the game doesn't 
>>> work quite right there either - it does work in David Keil's 
>>> emulator). I'm surprised it doesn't work in MESS.
>>> The strobing appears to be in the interrupt routine (both the write 
>>> to $ff02 and the read of $ff00). The routine starts at $c4fe - you 
>>> don't have to go far to see the *first* write/read of $ff02 and $ff00.
>>> By the way, what is RTSI?
>>> Brad
>  ><snip>

More information about the Coco mailing list