Subject: Re: [stella] BMI & BPL question From: Chris Wilkson <cwilkson@xxxxxxxxxxxxxxxx> Date: Mon, 29 Jun 1998 19:23:41 -0700 (PDT) |
> To check D6 you can use either of these... > > lda CXP0FB > bit #0 > bvs D6set But the BIT instruction doesn't support immediate addressing. (what a stupid thing to leave out!!!) So how does this work? Oh. I see what you're doing. If my understanding of the BIT instruction is correct, then it performs a logical AND of the accumulator and the operand and sets the Z flag accordingly. But it also copies bits 6 and 7 of the operand into the V and N flags respectively. If this is correct, then simply changing the addressing mode would achieve the intended effect: bit CXP0FB ; moves bits 6 and 7 to the status register bvs D6set ; checks bit 6 of CXP0FB bmi D7set ; checks bit 7 of CXP0FB -Chris -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/stella.html
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