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Detailed info on Basic USR command...

Posted: Sun Oct 15, 2006 8:10 pm
by dwhyte74
I've been looking for some detailed info regarding the Atari Basic USR command. What I need to know is how parameters are passed.

If I have a routine called with say:


How are they sent. I know that the you need to include a PLA at the start of the routine. What is first PLA pulling off the stack? The number of parameters? Now for my next PLA, will it be pulling the value for Y first, or the LSB of ADR(STRINGWITHML$)?

Any info would be appreciated.... Thanks

I found it...

Posted: Mon Oct 16, 2006 6:18 pm
by dwhyte74
Found the info I needed at ... nd_USR.php

I needed this information because I'm converting J.D. Casten's East80 ML routine to Quick.

I'll be the first to admit that 6502 assembler is not my strong point, but it's only 270 bytes long... I have it disassembled and hard coded (the 'ol Action! way), and hope to save about 20 bytes or so as there's no need to pass the parameters to the stack.

There is one thing that I'm still not sure of. It uses zero page address $00 for something. Not sure what for exactly yet.

Posted: Tue Oct 17, 2006 2:03 pm
by avram
Not to direct you away from the excellent Atarimania but there may be more programming help in the Progamming forum at