http://learn.cemetech.net/index.php?action=history&feed=atom&title=Z80%3AAnswers_3 2026-04-29T13:02:41Z Revision history for this page on the wiki MediaWiki 1.43.3 http://learn.cemetech.net/index.php?title=Z80:Answers_3&diff=140&oldid=prev 2016-02-05T07:34:19Z

<p>Created page with &quot;1. loop: cp b jr c,bigger jr z,endLoop inc c inc a jr loop bigger: dec c dec a jr loop endLoop: ... == Identif...&quot;</p> <p><b>New page</b></p><div>1.<br /> <br /> loop:<br /> cp b<br /> jr c,bigger<br /> jr z,endLoop<br /> inc c<br /> inc a<br /> jr loop<br /> bigger:<br /> dec c<br /> dec a<br /> jr loop<br /> endLoop:<br /> ...<br /> <br /> <br /> == Identify the Error(s) ==<br /> <br /> 2. <br /> <br /> inc b<br /> <br /> [[Z80:Opcodes:DJNZ|DJNZ]] uses B as the counter, so increasing B in the loop will result in an infinite loop<br /> <br /> 3. <br /> <br /> jp mUp ;assume mUp exists somewhere<br /> ...<br /> jp mDown ;assume mDown exists somewhere<br /> <br /> <br /> The error is not that mUp or mDown does not exist, it&#039;s that there is no check on any flag. It will jump regardless, so in this case it will always jump to mUp.<br /> <br /> &#039;&#039;&#039;Fixed code:&#039;&#039;&#039;<br /> <br /> <br /> jp z,mUp<br /> ...<br /> jp z,mDown<br /> <br /> 4. Nothing wrong with the code.<br /> <br /> 5. There&#039;s nothing wrong with the code. We want it to repeat 256 times, and since [[Z80:Opcodes:DJNZ|DJNZ]] decrements first, by setting B to zero it will first change B to 255, then repeat 255 times more. 255+1=256. Note that this is &#039;&#039;&#039;bad&#039;&#039;&#039; coding practice, though. Generally if you want a counter larger than $FF (255), you&#039;ll use BC as a 16 bit counter.<br /> <br /> {{lowercase}}<br /> [[Category:Z80 Assembly]]<br /> [[Category:Z80 Heaven]]</div>

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