>
> Yeah, I checked my code and DASM was turning it into an Absolute,Y for me
> without telling me.
LDA zeropage,Y isn't supported so it's converted to LDA absolute,Y.
Use LDA zeropage,X for the extra cycle speedup.
> questions: what does ADC do to the overflow flag, and how does BIT affect
> the flags? (I need a more complete reference..)
ADC will set the overflow flag if the result's most significant bit doesn't
reflect the correct sign of the result. $7F + $01 = $80 plus overflow.
$7E + $01 = $7F but no overflow.
BIT sets the N flag (BMI/BPL) based on the most significant bit of the
byte tested. It sets the V (overflow) flag based on bit 6. It sets the
Z flag based on the logical AND of the accumulator and the byte tested.
Many 2600 read registers use bit 7 (the most significant bit) and bit 6
for input data. That way a single BIT instruction can test either or
both bits quickly, and without disturbing the accumulator's contents.
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