Kantronics KPC-4 - Packet Mode; Command Mode

Packet Mode
Packet
radio
is
the
communication
of
digital
data
via
radio.
A
packet
is
a
group
of
characters
with
a
flag
and
header
at
the
beginning
and
a
checksum
and
flag
at
the
end.
A
flag
is
a
specific
character
used
to
signify
the
beginning
and
ending
of
a
packet.
The
header
is
information
concerning
who
the
packet
is
from,
who
it
is
to,
any
relay
stations
needed
to
get
to
the
destination
and
some
control
information.
A
checksum
is
a
complicated
mathematical
formula
that
produces
a
number
that
is
unique
to
the
combination
of
characters
that
are
in
the
packet.
This
unique
number
is
figured
by
every
station
that
handles
the
packet
and
if
it
does
not
match
the
number
that
is
in
the
packet
the
packet
is
thrown
away,
thus
error-free
communications.
A
packet
is
also
called
a
frame.
The
Terminal
Node
Controller
(TNC)
is
the
workhorse
of
packet
radio.
As
a
listening
device
it
hears
an
audio
signal
from
the
radio,
changes
the
data
to
digital
form,
determines
if
it
is
a
good
packet
and
sends
it
to
whatever
device
is
attached,
usually
a
computer.
As
a
relay
device
it
also
checks
the
packets
it
receives
and
determines
if
the
packets
need
to
be
resent,
then
does
so
if
appropriate.
As
a
sending
device
it
receives
digital
data
from
the
computer,
packetizes
it
and
changes
it
into
audio
tones
which
are
sent
out
to
the
radio.
The
rules
the
TNC
uses
to
do
all
of
this
is
called
a
protocol.
The
most
used
protocol
in
amateur
packet
radio
is
AX.25
Level
2
and
the
nitty
gritty
details
of
the
inner
workings
can
be
found
in
a.
book
named
AX.25
Amateur
Packet-Radio
Link-Layer
Protocol
available
from
the
ARRL.
Most
of
you
are
not
going
to
want
to
go
that
deep,
the
TNC
takes
care
of
the
nitty
gritty
work
for
you,
although
there
are
parameters
you
can
set
that
determine
how
efficiently
some
of
that
work
is
done.
In
this
section
of
the
book
we
will
be
discussing
the
fundamentals
of
how
to
get
on
the
air
and
how
parameters
interrelate.
The
default
parameters
will
get
most
everyone
on
the
air,
but
by
using
this
information
you
can
change
your
parameters
to
be
most
efficient
in
whatever
situation
you
find
yourself.
Command Mode
In
order
to
change
parameters,
or
give
any
other
instructions
to
the
TNC
you
must
be
in
Command
Mode.
This
is
the
mode
you
will
be
in
when
you
turn
on
the
TNC
(unless
you
have
changed
the
PMODE
parameter
in
the
KAM).
Once
you
have
left
Command
Mode
for
any
reason
there
is
a
parameter
called
COMMAND
that
determines
what
special
character
you
will
use
to
return
to
Command
Mode.
This
comes
defaulted
as
a
Ctrl-C.
(While
holding
down
the
control
key
press
"c",
then
release
both.)
All
parameters
are
described
in
alphabetical
order
in
the
Commands
Manual.
Whenever
you
enter
Command
Mode
the
TNC
will
send
a
prompt
to
your
screen
that
looks
like
this:
cmd:
Connected vs Unproto
There are two ways to send data in packet radio, connected or unproto (unconnected).
In
the
Connected
Mode
you
first
establish
a
connection.
Then
your
TNC
will
send
packets to that specific station and expects acknowledgments in return. If an
acknowledgment is not received the TNC will resend the data (depending on the
setting of AX25L2V2 it may send a poll first). The RETRY parameter will determine
how
many
times
this
is
done
before
the
connection
is
lost
due
to
bad
conditions.
If
the
acknowledgment
is
received
the
TNC
is
happy
and
will
send
more
data,
when
PACKET 11
©
Copyright
1989,
Kantronics,
Inc.
All
Rights
Reserved.
y
Duplication
of
this
manual
or
the
firmware
without
Version
2.85
permission
of
Kantronics,
Inc.
is
prohibited.
Operations
Manual