Re: [stella] Bensema's Playfield instructional

[Julian Squires <tek@xxxxxxx>]

On Fri, Aug 06, 1999 at 03:55:00PM -0700, Pete Holland wrote:
> I'm going through Nick Bensema's "How To Draw A Playfield" but am not
>      I thought STA stored what followed the command, from memory
> location or actual number, in the A register.  The book on 6502
> programming didn't mention anything about a comma like that.  What am I
> missing?

X and Y are registers. The comma indicates that the address in question (0,
here) is indexed by X before it is stored in A. 

The 6502 has a bunch of useful addressing modes. Two others you
may not have encountered yet (a good book on 6502 assembler will
help you, here):
 indirect absolute LDA ($8000)
 indexed indirect  CMP ($42, X)
 indirect indexed  ADC ($42), Y

Assembly is fun... also, not enough people use the undocumented
instructions (hint to list!)...

-- 
  -/ 
 |/|  Julian Squires <tek@xxxxxxx>
 /-                  <js@xxxxxxx>

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