At 05:47 PM 6/16/01 +1000, Andrew Davie helped me out:
Clear the carry flag before doing your addition :)
ie:
clc ; this one is necessary
lda Dealer
adc #1
and #3
sta Turn
clc ; this one might be optional
adc #MsgNumSouth
Many thanks, Andrew! (It turns out the second one is indeed optional.)
That's what I get for ignoring the advice of the book I used to learn ML
(_Machine Language for Beginners_ by Richard Mansfield). It says clc is
necessary before any addition and sbc is needed before any subtraction.
Why is this? The reason I didn't think I needed a clc instruction in the
code above is that I knew I was dealing with numbers that wouldn't cause
the carry flag to change. The value of Dealer is always between zero and
three, so adding one should make it between one and four. Why would a
carry flag that is set cause the addition to be off?
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