[aprssig] Trying to Specify the CRC-16-CCITT FCS

John Hansen john at coastalchip.com
Thu Jun 26 18:56:43 CDT 2014


Kenneth:

The source code for TNC-X (including the CRC) calculation is available on
my documentation page:

http://www.tnc-x.com/documentation.htm

The code is pretty thoroughly commented.  Note the starting value and the
xor manipulation that occurs at the end.

John W2FS



On Thu, Jun 26, 2014 at 4:34 PM, Kenneth Finnegan <
kennethfinnegan2007 at gmail.com> wrote:

> Gentlemen,
>
> I've been working on trying to specify the frame check sum we use for
> Bell 202/HDLC for my thesis. Do we really not have some kind of spec
> document like for AX.25 or APRS for layer 1? I've been able to find a
> few disjoint articles on the topic, and have been working out of ITU
> V.23 and V.42, but the checksum calculation has really got me stumped.
>
> Does anyone have a known-good code snippet that generates the correct
> CRC given a complete frame? Attached is what I have working off of a
> few examples online but they all seem to generate different results,
> particularly for empty sets... The endianess is a total mess, so which
> byte gets sent first?
>
> Attached: http://i.imgur.com/vfojzUB.png
> --
> Kenneth Finnegan
> http://blog.thelifeofkenneth.com/
>
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>
>
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