Memory Map - What use is Location 722 (0x2d2)

[+bhall408]

I have been resurrecting my old 80s games written in Atari Macro Assembler (now moved to ca65), and noticed that in all of them I was clearing location 722 to 0 during app init.

 

Anyone know off hand what that was used for/why I would have been doing it?

 

I was actually pretty liberal with comments in my source code (considering it was the 80s), but for some reason, no comment for that one.

 

My theory is that it is related to using E: and/or S:

 

(These are games that use custom multi-color characters, making use of PLOT, Drawto, etc calls to the driver, thus that theory...)

 

 

[+Stephen]

Mapping the Atari gives the following info (XL/XE only - in the 400/800 these bytes are listed as unused):

721,722 2D1,2D2 LOADAD

Used by relocatable loader routines.

[+bhall408]

1 minute ago, Stephen said:

Mapping the Atari gives the following info (XL/XE only - in the 400/800 these bytes are listed as unused):

Yep, I'd checked Mapping the Atari. I was about to check the OS source listings, but the PDF copy I have is not text searchable. It is also the case that a quick search may not find it, as the OS source didn't set the labels with explicit values, rather letting the assembler to that. ie, it isn't "LABEL = 722" but "LABEL .RES 1", which would make it harder to find in the source (if it is there).

 

[+selgus]

Removed, posted wrong address