CRC-CCITT in Tcllib

From: Patrick Moore (Patrick_Moore300_at_yahoo.com)
Date: 03/31/04 

Date: 31 Mar 2004 08:59:52 -0800

Hello,

I'm having trouble using the CRC package in Tcllib, which in large
part may be my lack of understanding with CRCs.

I'm receiving binary data (Async HDLC) from a mobile phone and want to
check the frames for errors. I thought I would start by verifying that
I can generate a known CRC (checkword) that is sent in a frame to
verify my method is correct. From some documents I have the CRC used
is CRC-CCITT-16, poly X^16+X^12+X^5+1, first initialized to all ones
and once calculated the one's complement of the CRC is transmitted.
Big Endian type is used for 16 and 32 bit words.

The known frame I have is: 1d 1c 3b 7e

So I'm trying to come up with 0x3b1c (post 1's complement) as the CRC
of 0x1d (request code 29) using the crc::crc-ccitt proc. I can't seem
to get close and I'm confused as to use 29, 1d, 0x1d, etc... as my
"message".

  crc::crc-ccitt -format 0x%X "message"

I'm been looking through the CRC package code and reading info
(overwhelming) on CRCs and now I'm really lost.

Any help would be much appreciated.

-PM

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