[Color Computer] [Coco] ASM Coders - Round two!

[James Diffendaffer]

>Hi again
>
>Thanks to everyone who helped last time - here's round two!
>The code as it stands can be found below
>If you compile and run it as-is, it'll clear half the screen

Ok, first of all... a little terminology problem.
Assembly language is assembled and high level languages like 'C' or
Pascal are compiled.  Now you know.

>but! when you simply uncomment the lines:
>    *lda #$32
>    *sta $FFA3

Ok, next problem.  While using $FFA3 is perfectly legal you might want
to start naming hardware registers.  There's nothing worse than
looking back through some code you haven't touched in a while or
someone elses code and having to go lookup what is at a given address.

$FFA3 is a GIME register for the MMU.
 
>It clears half the screen, and draws some colored garbage 3/4 of the
>way 
>down the screen
>
>I can't understand why it's doing this
>
>am I trying to allocate memory that I'm not allowed to touch? Am I 
>swapping *out* some memory that's otherwise being used?

Another terminology thing.  Allocating memory is usually used to
describe asking an OS routine to give you a pointer to a free block of
RAM of the size you need.  

You can touch any RAM you want but you have to understand what the
hardware is actually doing.
 
I'm guessing the garbage is in the block of memory you just switched
in and it now lies in your video display area.

Do you really need to mess with the MMU yet?






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