Post by thread:help Mpasm

part 0 844 bytes <META content=text/html;charset=iso-8859-1 http-equiv=Content-Type> <META content='"MSHTML 4.72.3110.7"' name=GENERATOR> </HEAD> <BODY bgColor=#ffffff> <DIV><FONT size=2>Hi, Piclisters,</FONT></DIV> <DIV><FONT size=2></FONT> </DIV> <DIV><FONT size=2>What's do the following sentence:</FONT></DIV> <DIV><FONT size=2></FONT> </DIV> <DIV><FONT size=2>addlw  0 - 1</FONT></DIV> <DIV><FONT size=2></FONT> </DIV> <DIV><FONT size=2>is in assembler file and i can not understand it</FONT></DIV> <DIV><FONT size=2><BR></FONT> </DIV></BODY></HTML> </x-html>

On Tue, 7 Sep 1999 10:16:30 -0400 felix centeno <spam_OUTfcentenoTakeThisOuTIAMNET.COM> writes: > Hi, Piclisters, > > What's do the following sentence: > > addlw 0 - 1 This adds -1 to W. -1 in two's complement notation is 0xFF, so you could use "addlw h'0ff'" instead. I've had some (I think very old) versions of MPASM not process 'addlw -1' correctly. So using the 0 - 1 construction is safer. After the instruction executes, the value in W will be 1 less than it was before. Consider it a "decrement W" operation. It will also roll under from 00 to 0xFF. The Z flag will be set if the new value of W is zero. The C flag will be set if the old value of W was not zero. Or, you could say that the C flag will be clear only if the new value of W is 0xFF. The DC flag is also affected. ___________________________________________________________________ Why pay more to get Web access? Try Juno for FREE -- then it's just $9.95/month if you act NOW! Get your free software today: dl.http://www.juno.com/dynoget/tagj.

Hi, it subtracts one from the actual content of W, as the famous SUBLW instruction does the opposite (subtracts W from literal). It is a trick how to realize subtraction from W as normal in other processors. I hope this helps. Regards, Imre On Tue, 7 Sep 1999, felix centeno wrote: {Quote hidden}> Hi, Piclisters, > > What's do the following sentence: > > addlw 0 - 1 > > is in assembler file and i can not understand it > > >