Sweet. I have run into something like what you are talking about here:
Quote:
00E25F A90000 lda ax, #0x0000
00E262 89090058 mpy #0x5800 ; Branch target from E25D
00E266 8928 xab
00E268 8D0410 sta ax, 0x1004
00E26B F8 sem ; m:1 x:0
00E26C 42AD0510 lda bl, 0x1005
00E270 F00D beq 0xe27f
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I didn't include it but if A is greater than or equal to 0 e25f is skipped and the value in A is multiplied by hex 5800. So it looks like either A or hex 0000 is multiplied by hex 5800. Then the xab followed by the sta ax, 0x1004 is swapping A and B (necessary because of the way the processor works, I suppose), putting the most significant 16 bit value in A and storing it at 1004. Then the most significant 8 bit value is loaded into bl from 1005. The program then branches to e27f if the zero flag is set, but set by what? Is it set if the value loaded into bl is 0? Or is it looking way up at the mpy to see if that equals zero?