Kantronics KPC-4 - Page 44

Let's look at data from the TNC to the computer. First, all information flowing in this
direction is data. No special messages are sent from the TNC to the computer in KISS
Mode. The only data flowing in this direction is that received through the radio link.
Every "frame" of data sent from the TNC will begin and end with a special FEND
character. This character is the ASCII code $C0 (hex) or 192 decimal. The second
byte of the data will be the data type, and will always be a $00. This means that the
following information is data. If the data actually contains the FEND character ($C0)
it will be necessary to tell the computer that the $C0 it receives is not the end of the
frame, but simply is more data. This is accomplished by replacing the $C0 character
with a special sequence consisting of a FESC ($DB) followed by a TFEND character
($DC). One final special sequence which could be sent from the TNC to the computer is
a FESC ($DB) followed by TFESC ($DD) This is translated into $DB by the computer
program.
Now, looking at data flowing in the other direction, that is from the computer to the
TNC. There are five possible commands that you may need to issue to the TNC from
the
computer,
and
they
basically
concern
setup
parameters.
These
are
commands
needed to set TXDELAY, PERSISTENCE, SLOTTIME, FULLDUP, and finally, a
command to exit the KISS Mode of operation. The only other data which the computer
may send to the TNC in KISS Mode is data which is to be transmitted over the radio
(HDLC) channel. The data coming from the computer must also begin and end with
the same FEND character as is used for data coming from the TNC. All special
character sequences must also be used to send the FEND, and FESC characters
as data.
Each of the commands is assigned a command type number as follows:
TYPE FUNCTION
0 Data to be transmitted
1 TXDELAY - second byte contains txdelay in 10 ms increments
2 PERSISTENCE - second byte contains persistence value
3 SLOTTIME - second byte contains slot interval
255 ` Causes exit from KISS Mode
For
example,
if
I
want
to
set
the
TXDELAY
in
my
KISS
Mode
TNC
to
100
milliseconds,
the
computer
would
send
the
following
bytes to the
TNC:
CO 01 0A CO
and to send a data packet saying hello would be:
CO 00 68 65 6C 6C 6F CO
It is important to note that this data packet does not contain any addressing
information,
and
therefore
cannot
be
sent
via
AX.25
protocol.
All
of
the
addressing
and formatting of the addresses must be done in the computer and sent as a data
packet to the TNC.
A _ —_— _—— ___——______ —_— E AAAOAOAOS—Á
. E © Copyright 1989, 1990, Kantronics, Inc. All Rights Reserved.
Version 3.0 Aug. 13, 1990 Duplication of this manual or the firmware without
Operations Manual permission of Kantronics, Inc. is prohibited.