Re: [stella] Hello World

Subject: Re: [stella] Hello World
From: Jeff Johnston <jeffryj@xxxxxxxxxxxxx>
Date: Sun, 7 Jul 2002 17:48:08 -0700 (MST)
Welcome!

> This is the command:
> LDA  playf0,X      ;load in the data for playfield 1
>      STA  PF0

I "think" in Basic, so here is the Basic version:
A=playf0(X)

We know that playf0 is at a certain location in memory (you set it with
the EQU at the beginning of your program).. X is an offset from that
location.  In other words, it's an array (you can also use ,Y as an array
offset, but not A).  But getting back to your example, if X=0 then you
might as well have said: LDA playf0, if X=1 then LDA playf0+1, etc, but
this way it's not stuck to a certain location.  This is good for loops,
where you'll use X or Y as your loop variable.

calamari


>
> Also, what is X contributing to the process in the above LDA statement?
>
> That'll do for now, any help appreciated. I'm also seeking any baby-step
> docs similar to Kirk's redline demo... aka liberally commented source code
> for newbies! :)
> Thanks!
> Brian
>
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Current Thread
  • [stella] Paddles, (continued)
        • Jeff Johnston - Sun, 7 Jul 2002 18:39:33 -0400 (EDT)
        • Jeff Johnston - Sun, 7 Jul 2002 18:51:03 -0400 (EDT)
        • Ruffin Bailey - Sun, 7 Jul 2002 19:51:25 -0400 (EDT)
        • Roagie - Sun, 7 Jul 2002 20:20:36 -0400 (EDT)
        • Jeff Johnston - Sun, 7 Jul 2002 20:47:24 -0400 (EDT) <=
        • Jeff Johnston - Sun, 7 Jul 2002 20:48:56 -0400 (EDT)
        • Roagie - Sun, 7 Jul 2002 21:09:51 -0400 (EDT)
        • Erik Eid - Sun, 7 Jul 2002 21:49:49 -0400 (EDT)
        • Roagie - Sun, 7 Jul 2002 22:38:16 -0400 (EDT)