Scott,

Your test loop is comparing the lo byte of the CRC twice and ignoring the hi 
byte!

Bob Ammerman
RAm Systems

----- Original Message ----- 
From: "Scott Dattalo" <scott@dattalo.com>
To: <piclist@mit.edu>
Sent: Monday, December 27, 2004 4:03 PM
Subject: [PIC] CRC16


>
> Quite a while back, Ashley Roll, Dave Dribin and I were kicking around 
> CRC16 implementations for a PIC. Just recently, Johan Bodin asked about 
> the CRC algorithm for the Polynomial A001, which as he says, sounds an 
> awful lot like the reversed 8005 polynomial. I didn't realize at the time 
> he asked that it was indeed the reversed 8005 polynomial and hence the 
> CRC16 algorithm.  So, I merrily went off and wrote a new optimized 
> version. This one is only 23 instructions, which is 9 fewer than the 
> previous version! It's isochronous, taking 23 cycles, and requires no 
> tables.
>
> Here's the routine:
>
> http://www.dattalo.com/technical/software/pic/crc16.asm
>
> Here are other CRC routines:
>
> http://www.dattalo.com/technical/software/pic/crc.php
>
> Scott
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