[Coco] Re: Technical: PIA Help

Robert Gault robert.gault at worldnet.att.net
Fri Dec 2 09:21:51 EST 2005

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

More information about the Coco mailing list