I've been seeing the messages on various error checking routines such as
Hamming and CRC. I had a project that uses 32 bit "packets" to transfer
information. In order to ensure the data was not corrupted (and also to
obtaing frame sync) an 8 bit checksum was added to make a 40 bit frame.
The checksum of the 32 bits was then compared to the last byte of the
frame to determine the validity of the data. I'm not sure if it was the
best way but it was easy. I've read that the checksum method is not as
sensitive to detecting errors as other methods and I have no idea of the
odds of this method giving a correct checksum with errors in the data.
Does anyone know of any references that would discuss this or know the
answer. Thankyou in advance.

Here is the code that does the checksum checking:

;*****************************************************
;Checksum Sub
;*****************************************************
chksum   bcf   flags, chksum_ok     ;clear checksum flag
         movf  frame0, 0            ;move frame0 to W
         addwf frame1, 0            ;add frame1 to W
         addwf frame2, 0            ;add frame2 to W
         addwf frame3, 0            ;add frame3 to W
         xorwf frame4, 0            ;XOR checksum frame with W
         btfsc status, z            ;result = 0?  q=yes
         bsf   flags, chksum_ok     ;if yes, set checksum flag
         retlw null                 ;return with null



;********************************************************************

Dan Mulally