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Karl G

Loading an address with a variable offset

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If I want to create a pointer to data in a table with a variable offset into the data, what is the syntax? Here is what doesn't work:

 

    lda #<enemy_bitmaps_1,y
    sta EnemyPtr
    lda #>enemy_bitmaps_1,y
    sta EnemyPtr+1

I have confirmed via the Stella debugger that I am loading the correct offset into Y, but it is not pulling the correct data when I try to use the pointer. What am I doing wrong here?

 

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LDA - Immediate and Absolute,Y are two distinct address modes, they can't be used at the same time. In a better compiler that would cause a compile time error, or at least a warning, but with dasm the Absolute,Y mode appears to have priority.

 

I suspect what you're after is covered in step 14 - add animation of my tutorial, though I used Absolute,X instead of Absolute,Y (either will work).

 

post-3056-0-51833900-1546980735.png

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