Thanks to all who replied to my query.
It is nice to know that there are people around who are willing to pass on
their knowledge to others.

I have now got the parity side of the program working.

I used:

temp = 0;
for (count = 0; count <8; ++count)
	{
	Temp ^= ((variable >> count) & 1);
	}

Once again, thanks for the help.


-----Original Message-----
From: Dmitriy Kiryashov [mailto:vze27bym@verizon.net] 
Sent: 12 June 2006 23:28
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] calculating parity bits

Hi Walter.

John Payson's example was shorter/faster :)
Originally in asm, can be easily ported to c if required.

	rrf	ch,W	;x = ch >> 1
	xorwf	ch,F	;ch ^= x
	swapf	ch,W	;x = ch >> 4 | ch << 4
	xorwf	ch,F	;ch ^= x
	btfsc	ch,2	;if ( ch & 4 ) ch++
	incf	ch,F	; or incf ch,W if needed
			;bit.0 has a parity

WBR Dmitriy.

PS. I've seen John's posts recently in htsoft forums.


Walter Banks wrote:
> 
> One of my favorite compromise parity checkers was
> originally implemented in hardware and published
> in electronics design. In the original the ac was declared as
> an accumulator it can be replaced as a local variable.
> 
> If you use this any public way credit the sources.
> 
> It is a clever algorithm
> 
> w..
> 
> int parity(char ch)
>   {
>    /*
>      Implemented in C Based on the original
>      hardware implementation in Electronics design.
>      Walter Banks Byte Craft Limited
>      September 1991
> 
>      Electonics Design Aug 22, 1991
>       Noor Singh Khalsa
>       EG&G
>       P.O Box 809,
>       MS E-1, Los Alamos, NM 87544
>       (505) 667-0200
>     */
> 
>    ch = (ch >> 1) ^ ch ;
>    return (((ac = (((ch >> 2) ^ ch)) & 0x11) == 0) ? 1 : ((ac ^ 0x11) ==
0) );
>    if ((ch = (((ch >> 2) ^ ch)) & 0x11) == 0) return 1;
>    if ((ch ^ 0x11) == 0) return 1;
>    return 0;
>   }
> 
> Brian Millward wrote:
> 
> > I am fairly new to PIC programming and I am building a radio clock to
decode
> > Rugby MSF transmissions.
> >
> >
> >
> > It all works, but I have not done any parity checking.
> >
> >
> >
> > I have some BCD variables and a checksum bit and I need to check that
all
> > the bits add up to an odd number.
> >
> >
> >
> > I have thought of checking the lsb, then shifting right and repeating
etc,
> > adding all the bits together, but I am sure that there is an easier way
I
> > just cannot think of it
> >
> >
> >
> > Apologies for seeming to be a bit dense, but I am trying to master it.
> >
> >
> >
> > By the way, I am using CCS 'C' compiler.
> >
> >
> >
> > Thanks for any help you may be able to give.
> >
> >
> >
> > Regards ... Brian
> >
> > --
> > http://www.piclist.com PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> 
> --
> http://www.piclist.com PIC/SX FAQ & list archive
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> http://mailman.mit.edu/mailman/listinfo/piclist



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