Over the weekend, I was showing Linux and Packet radio and for some reason I could not talk to my TNC, a KPC 3+. It was at this point that I realized I had forgotten more about Linux (and minicom) than I had about the commands needed to control the TNC. So, in the interest of helping save you some time, here is a quick write up on using minicom with a USB/Serial adapter to talk to your TNC, specifically, a KPC.
Minicom is an old school program that is available for most of the distributions but may not be installed by default. The good news: it is in all the repositories, so you can pull it down and install it quickly.
It is a serial terminal program that runs from the command line, but can sometimes be a little fussy to get working, and I will admit that I have not used minicom with a USB/Serial converter.
First, you have to know what tty port your USB/Serial converter is
on. So, plug it in, give it a minute and then type at a console port:
dmesg | grep tty
You should get something like this back:
kg4giy@kauai:/$ dmesg | grep tty
[ 0.001982] console [tty0] enabled
[ 686.529224] usb 2-2: pl2303 converter now attached to ttyUSB0
In this case, the converter is attached to ttyUSB0, you when you
configure minicom, you want to use /dev/ttyUSB0 as the serial port
To start minicom then (assuming you have not configured it, but you
know the modem speed of the TNC) type:
$ sudo minicom -s
Note that minicom requires root privileges. You will be prompted for
Select "Serial port set up" from the list with the cursor keys and set
the serial device and the Bps/par/bits (8/N/1 and whatever the speed
of your TNC is). Press , Save setup as dfl to save your
settings and then select Exit to enter minicom.
Turn on the TNC. Press once or twice if you do not get the
TNC cmd: prompt and you should now have control of the TNC.
When you are done, A then Z will bring up the help menu and you
can exit by pressing Q or A Q to exit.
One thing to note. Minicom has a much smaller set of connection speeds. For overall interoperability, it is best to set the baud rate of your TNC to 9600, with 8-n-1 for parity. This will facilitate connectivity with a multitude of devices, including a simple VT220.
I hope this saves you all a few minutes!