[aprssig] TNC2 FoxDigi - COM problem

Julian, G4ILO julian.g4ilo at gmail.com
Sat Feb 5 09:39:16 EST 2011

Hi Alexandru.

I have only just joined this group but wanted to reply to your message
which I saw in the archives. I have just built one of the WB8WGA TNCs
as modified by DJ7OO and ZL2AME using a pair of transistors instead of
the MAX232 and I have found the same problem. It is such a common
problem that I am surprised no-one has provided an updated firmware.

The problem with lack of response to commands is that the firmware
looks for a line feed to terminate commands, where most terminal
programs (and also software like UI-View) only provide carriage return
characters. The TNC also has a timer that executes whatever has been
typed in if the line is not terminated by a LF and it is this that
causes the few seconds delay to respond to commands. This problem is
quite easily fixed in the firmware. This is not enough to make it
usable with Ui-View, though I don't think the 3,000 changes mentioned
by Chris G4HYG are all necessary. In fact I have it working with
Ui-View at the moment.

The next problem is that Ui-View does not display the received
packets. That is because the TNC does not put the packet type e.g.
"<UI>" in the decoded packet. I'm not sure how to overcome this other
than by faking it and putting it in every packet. Fortunately there is
an option in Ui-View for relaxed packet checking that makes it ignore
the lack of "<UI>" so there is the easy way round it that does not
consume any PIC memory space.

The next problem is if you are sending much out to RF you will find
the TNC drops out of Converse mode intermittently. There is a timer in
Converse mode that causes an exit back to command mode if characters
are typed and not terminated and that appears to be the cause of this.
Commenting out two lines of code to disable the timeout solved that

The UNPROTO command uses the nonstandard format UNPROTO tocall V
digi-1 V digi-2 V digi-3. There seems to be a bug in the code and I
cannot get it to accept UNPROTO APRS V WIDE1-1 V WIDE2-1 though it
will accept something like UNPROTO APRS V TRACE V WIDE1-1. I am not
sure why that is at the moment. I have modified the command to use the
form UNPROTO APRS V digi-1,digi-2,digi-3 which is what UI-View will
use, but if it won't accept digi-2 or digi-3 then it isn't a problem
for me so I'm not sure I will spend much time on that particular

A more major problem is that anything that is sent to the TNC whilst
it is transmitting is ignored. THis is quite a problem for me as I do
a lot of mesaging with my HT through an IGate and if I send a message
to a server and get an ack back followed instantaneously by another
message, the message is lost and only the ack is received, although
the terminal shows UI-View sent both to the TNC. Therefore I think I
need to implement flow control, if possible.

I know nothing about PIC programming or assembler so this is being a
real learning process for me with a lot of trial and error. If I
eventually solve all of these problems then I will publish the revised
source code. Check my blog for progress. In the meantime if you would
like a copy of the HEX of my current working version send me an email.
If any members of this esteemed group have done any work on this and
have bits of code they could send me that might help solve some of the
outstanding problems I would be very grateful. :)

alexandru yo2ldk at yahoo.com wrote:

hi for all,
 i make 2 pcs. TNC with PIC16F88 after FOX DIGI schematic, and MAX232
for serial
  When I try to connect with ui-view, fail, I look frame error on com 1; if
I give the command display, show me the settings after a few seconds.
 So there is a delay on the RX line, because if I connect the
modem, my message appears instantly "Modemless ....."  that's why I
can not make
any connection in the UI-View, I guess.
 has anyone encountered this symptom?

Julian, G4ILO
G4ILO's Shack: www.g4ilo.com

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