Re: [stella] My code is broked!

Subject: Re: [stella] My code is broked!
From: "Chris Larkin" <clarkin@xxxxxxxxxxxxx>
Date: Wed, 8 Oct 2003 18:22:09 -0700
This sounds right now that you say it :-) I even considered it yesturday, but I wasn't sure $00 was a valid high byte for whatever reason.
My main confusion comes from's explanation of

Affects Flags: S Z

MODE           SYNTAX       HEX LEN TIM
Immediate     LDA #$44      $A9  2   2
Zero Page     LDA $44       $A5  2   3
Zero Page,X   LDA $44,X     $B5  2   4
Absolute      LDA $4400     $AD  3   4
Absolute,X    LDA $4400,X   $BD  3   4+
Absolute,Y    LDA $4400,Y   $B9  3   4+
Indirect,X    LDA ($44,X)   $A1  2   6
Indirect,Y    LDA ($44),Y   $B1  2   5+
This lead me to believe only the low byte is used.  Silly me
----- Original Message -----
From: Jason Rein
Sent: Tuesday, October 07, 2003 8:07 PM
Subject: Re: [stella] My code is broked!


I'm still learning Indirect Y addressing (and writing a "how to" as I go along in case I forget later) but I think you may need to initialize both the hi and lo byte of the address (since Indirect Y expects a 16-bit address).

For example, you're stuffing the value #$B0 (least significant byte of the address) in tmpVar3 but when you go to dereference it later (with "lda (tmpVar3),y"), it's reading the address as "$xxB0" where "$xx" is garbage.

Try this...

lda #PlayerHand
sta tmpVar3
lda #0
sta tmpVar3+1

lda #Player3
sta tmpVar4
lda #0
sta tmpVar4+1

We're simply putting "$00" as the most significant byte of the address so the tmpVar3 pointer will look like "$00B0" and the tmpVar4 pointer will hold "$00A0". Oh, and be sure both tmpVars are 2 bytes in size!

I hope that helps. If not, we'll both learn something! :)


On Tuesday, October 7, 2003, at 07:33 PM, Chris Larkin wrote:

It could just be that I still don't fully understand indirect addressing... But this should work?
I know this loop does not replace the first byte in either location, but it should "swap" the others... However
my results are not very good :-) What am I doing wrong?
PlayerHand = $B0 ; -> $B6
Player3 = $A0 ; -> $A6
     LDY #7
     LDA #PlayerHand
     STA tmpVar3
     LDA #Player3
     STA tmpVar4

     LDA (tmpVar3),y
     STA tmpVar2
     LDA (tmpVar4),y
     STA (tmpVar3),y
     LDA tmpVar2
     STA (tmpVar4),y
     BNE TradeLoop
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