Re: A82: Re: i gots a kwestun 4 yous people

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Re: A82: Re: i gots a kwestun 4 yous people


PE = Parity Even => P/V = 1
PO = Parity Odd => P/V = 0

Overflow => P/V = 1 

So PE is true if there was an overflow, and PO is true if there was not.

Dines

_______________________________________

Dines Justesen
Email: dines@post1.com or
       c958362@student.dtu.dk
WWW  : http://www.gbar.dtu.dk/~c958362/
_______________________________________

On Thu, 5 Mar 1998, L0rdG0aT, Lord of sodomy and of darkness wrote:

> 
> thank you for that information... it will be useful not only to me, but a
> friend of mine too.
> one more question... on the case of the usage of the parity bit on
> overflow...
>   JP PO == says it overflowed?
>   JP PE == says it didn't overflow?
> 
> or is it the other way around?
> 
> thank you again...
> -Greg
> 
> On Thu, 5 Mar 1998, Dines Christy Justesen wrote:
> 
> > 
> > As usual from my favorite Z80 asm book :
> > 
> > P/V : Parity or overflow flag. Parity (P) and overflow (V) shere the same
> > flag. Logical operations affect this flag with the parity of the result
> > while arithmetic operations affect this flag with the overflow result.
> > ... If P/V holds overflow, P/V = 1 if the result of the operation produced
> > on overflow.
> > 
> > So the Z80 has got a way to detect overflows. JR does not support this
> > flag, but JP does, so you can just use JP PO and JP PE to check for
> > overflows.
> > 
> > Dines
> > -----Original Message-----
> > From: Greg R Milewski <l0rdg0at@juno.com>
> > To: assembly-82@lists.ticalc.org <assembly-82@lists.ticalc.org>
> > Date: 3. marts 1998 03:10
> > Subject: A82: i gots a kwestun 4 yous people
> > 
> > 
> > >
> > >is there any way to detect a register overflow (like "jr o, label") with
> > >the z80?  it could really help if there was an instruction... else, is
> > >there a simple routine i can use?
> > >
> > >thanx,
> > >-Greg
> > >
> > >_____________________________________________________________________
> > >You don't need to buy Internet access to use free Internet e-mail.
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> > >
> > >
> > 
> > _______________________________________
> > 
> > Dines Justesen
> > Email: dines@post1.com or
> >        c958362@student.dtu.dk
> > WWW  : http://www.gbar.dtu.dk/~c958362/
> > _______________________________________
> > 
> 
>
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