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[aprssig] AX.25 'H' flag

Curt, WE7U archer at eskimo.com
Mon Nov 14 16:46:00 UTC 2005

On Mon, 14 Nov 2005, Wes Johnston wrote:

> I am indeed talking about the kiss/ax.25 spec...  I used the CONV mode
> method of H bit indication... so a little mixing of terms here... but I
> did see a difference in the way the kpc3's and pacomms dealt with H bits.

It's that mixing of terms that is causing the confusion.  If you're
in CONV mode watching the TNC's ASCII-text version of the headers,
all bets are off.  In that case you absolutely have to use your
method of checking from the right end of the header to find the
first '*'.  Unfortunately that header info DOES NOT indicate that
all of the 'H' bits have been set from the left up to that point.
They have though.

> I think Bob said it would be chaotic... and he's right... but it's what
> I saw.  Unfortunately, I don't remember which TNC filled up the h bits,
> and which on just set the current bit.

All of them fill up the 'H' bits, else nothing would work right.
It's just the "CONV" version of the header which is whacko here.
There are several ways to represent the header info in "CONV" mode.
If you were looking at the KISS frames, you'd see all of the 'H'
bits filled up through the last one used.  Every time.

Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
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