ADI - ADP frame start, end and escape characters

Erich R. Oetting oettier at stamps.stortek.com
Tue Jan 28 07:41:23 PST 2003


* From the T10 Reflector (t10 at t10.org), posted by:
* "Erich R. Oetting" <oettier at stamps.stortek.com>
*
In addition to other constraints, we should attempt to choose Start of 
Frame (SOF), End of Frame (EOF) and Escape (ESC) characters for ADP 
that avoid byte stuffing in commonly sent frames.

The current frame header format has one unused bit in the second header 
byte.  If SOF, EOF and ESC all have bit 00001000b set, the second 
header byte will never be escaped.   This same bit is also unused in 
the first header byte.  It may however occur in the two size bytes of 
the header.

The current definition for VHF data also has an unused bit in all 
bytes.  If SOF, EOF and ESC all have the 01000000b bit set, no VHF 
data bytes will be excaped.  Using SOF, EOF and ESC bytes with both 
these bits set (i.e. 01001000b) will avoid escape sequences in the 
first two header bytes and any VHF data bytes.  The size bytes in 
the header will also not be escaped for frames under 72 bytes in length.

Based on this, I would suggest using the following characters for SOF, EOF 
and ESC:

Start of Frame - 5Bh - 01011011b - "["

End of Frame   - 5Dh - 01011101b - "]"

Escape         - 7Fh - 01111111b - "~"



 ... Erich Oetting
 

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