I get a little nervous when you say "I need to check that all the bits add 
up to an odd number".  It is my experience that parity bits are used in each 
byte during transmit (or storage), not as a check on the entire message.

You have a good  idea about shifting and counting the LSB (Least Significant 
Bit) each time.  There is a simple way to do that because the LSB of the 
count of bits will show if it is odd or even parity.  Start by clearing the 
result variable.  then for eight times, add the byte under test to the 
result and shift the byte under test to right by 1.  There is no need to do 
the eight shift as you have finished counting the eight bits by then.  Then 
just look at the LSB in the result variable, if it is a 1 then byte has odd 
parity.  You don't need to be concerned with what the rest of the result 
variable contains.

Bill

----- Original Message ----- 
From: "Brian Millward" <b.millward@ntlworld.com>
To: <piclist@mit.edu>
Sent: Friday, June 09, 2006 5:20 PM
Subject: [PIC] calculating parity bits


>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
>
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