Hi Scott,

You might not have read the whole application note (AN27), so let me just
add that in addition to the DOW algorithm, Dallas Semiconductor *does*
present the CRC-16 algorithm (polynomial X^16 + X^15 + X^2 + 1) later on in
the application note (see page 9). Thanks for contributing the links to your
code.

Best regards,

Ken Pergola



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Scott Dattalo
Sent: Tuesday, August 12, 2003 6:30 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: PIC18F fast CRC-16 LUT code *not* wanted, but rather
you can have it


On Mon, 11 Aug 2003, Ken Pergola wrote:

> Perhaps the following code may be useful to someone either now or in the
> future (at least it's nice to have in your engineering toolbox).
>
> I've adapted the fast look-up table CRC-16 from the Dallas Semiconductor
> Application Note 27 to the PIC18F architecture:

Actually the CRC algorithm in AN27 is *not* CRC-16. Read the bottom of
page 2 - their algorithm is something they call "DOW CRC" for "Dallas One
Wire" and it's an 8-bit CRC. If you want another C-implementation then
check out:

http://www.dattalo.com/technical/software/pic/crc_8bit.c

If you want the assembly version then:

http://www.dattalo.com/technical/software/pic/crc_8.asm

It takes only 20 cycles (and is only 19 instructions).

If you do want the CRC-16, or more specifically the CRC-CCITT-16, then
check out here:

http://www.dattalo.com/technical/software/pic/crc.php

By the way, the CRC-CCITT-16 algorithm can be implemented in 5
instructions on an ARM.

Scott

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