Configuring Serial TNC Ports

Terminal-Node Controllers (TNC) or radios containing built-in TNCs are connected through a computer serial port using the KISS protocol.

To add a new TNC port, click the Add button on the Configure Ports tab. The port editing dialog will appear. Set the port type to Serial_TNC.

The other parameters you will need to specify for the TNC are:

• the name of the port to which the TNC is connected. On Microsoft Windows, this will be a COM port (COM1, COM2, etc.). On Linux, this will be a /dev/ttyS port (ex. /dev/ttyS0) or a USB serial port (ex., /dev/ttyUSB0), although the console port on a Raspberry Pi appears as /dev/ttyAMA0. Similar device names will be used on other Unix derivatives. Note that on Linux and Unix systems, you will need the access right to access serial ports. Typically, this will be membership in a group owning the serial ports, such as dialout, tty, or uucp.
• The baud rate at which the TNC will be communicating with the computer (typically, 9600 baud). Ensure that the TNC is set to the same speed as you configure this port to. Note this is independent of the baud rate transmitted over the radio (1200 baud on 2 meters, 300 baud on HF, and 9600 baud on UHF). Note also that this may be meaningless for TNCs or radios with direct USB connections, such as the Kenwood TH-D72. For devices where the baud rate is meaningless (or where the operating system's driver for the serial port actually fails if YAAC attempts to configure the port baud rate), the baud rate can be specified as blank, indicating that YAAC should not try to set the baud rate at all.
• The callsign you will be using to identify your transmissions over this port. This should be your legal government-assigned callsign with an optional numeric SSID suffix from 1 to 15.
• Whether or not you want to allow YAAC to make transmissions through the port. If left disabled, you will only be able to monitor APRS traffic through this port. You must specify a callsign to be able to transmit.
• Whether your TNC requires hardware flow-control (using the RTS and CTS modem control signals) to be enabled for your TNC. Note this is only useful if actual RS232 connections are being used with at least 5 wires in the cable. Also, specify whether the DTR signal should not be activated; normally, the DTR signal should be enabled to indicate to an external modem device (like a TNC) that the computer is present and powered up. However. some modems perform hardware flow-control with the DTR signal instead of the RTS signal, which is not presently supported by YAAC (actually, not supported by the JSSC library used by YAAC). Note that hardware flow control assumes that the TNC will provide an active DSR (Data Set Ready) modem control signal to indicate that the TNC is actually present. If your TNC or cable does not provide DSR, select the Kenwood work-around to disable checking for DSR.
• Whether your TNC is a Kenwood radio with built-in TNC that may react to certain character sequences as commands from Kenwood's Memory Control Progran (MCP) that would misconfigure the radio. Unless you are using a Kenwood radio's built-in TNC, this should be unchecked.
• Whether the radio on this port is tuned to the HF bands. By default, YAAC assumes usage on the VHF and UHF bands where higher bandwidths are permitted and digipeating is normally used.
• The command for YAAC to issue to switch the TNC into KISS mode. Most TNCs use the command set introduced with the TAPR TNC-2, start up in command mode, and switch to KISS mode with the commands:
  KISS ON
RESTART
  However, not all TNCs are TNC-2 compatible. Some TNCs are built for KISS-only, and do not need to be switched. The Kantronics KPC-3 and Byonics TinyTrak TNCs use non-TNC2-compliant commands to enter KISS mode (and the TinyTrak can only be switched immediately after the unit is rebooted). In any case, you need to specify the correct command if one is needed for your TNC; if you do not specify one, YAAC will default to assuming a KISS-only TNC (or one manually pre-configured to default to KISS mode). You may select one of the other known types from the drop-down list, or type a command sequence of your choice (using \r to represent the carriage return character). Only if a command was needed to switch your TNC into KISS mode will it be automatically switched out of KISS mode when YAAC is exited. The following escape sequences may be used in the command expression:

  Escape sequence	Meaning
  \r	Send a carriage return control character and pause sending for 300 milliseconds.
  \n	Send a newline or linefeed control character.
  \t	Send a horizontal tab control character.
  \0	Send a null control character.
  \\	Send a backslash character (this is needed to differentiate a literal backslash from any other escape sequence).
  \f	Send a form feed control character.
  \'	Send a single quote or apostrophe character.
  \e	Send an escape control character.
  \"	Send a double quote character.
  \w	Don't send anything, but wait for 1 second.

• The sub-list of aliases that will be digipeated through this port, based on the total list of known aliases defined in the general configuration. If YAAC receives a message with one of the checked digipeat aliases and this port is enabled for transmission, the message will be re-broadcast through the radio on this port. If no aliases are selected, this port will not digipeat. Multiple aliases can be selected. The aliases must also be enabled for digipeating on the configuration dialog's Digipeat tab.
• Which of potentially several beacon definitions will be transmitted through this port. If none is checked when the port configuration is saved, the default beacon will be used (and will show up as checked when this configuration panel is next opened). To specify that a beacon should not be sent out this port, a beacon should be selected that is not enabled on the Beacon tab of the expert-mode configuration dialog.
• The protocols that can be transmitted through this TNC. Generally, only one protocol should be used on a given RF channel to avoid confusion of other stations and wasting of bandwidth. Which supported protocols should be transmitted out a TNC port is specified by checking the corresponding checkboxes. Note that YAAC will support receiving all protocols through one TNC port, recognizing which protocol is in each AX.25 frame by the PID field; this merely restricts which protocols YAAC will send on a port. The "raw AX.25" protocol supports connected-mode packet operation.
• Whether transmission through this port should be delayed until an assigned transmit timeslot at some offset after the beginning of a repeating interval, and how long this timeslot is before the next timeslot (presumably assigned to some other station) starts. Note that timeslotting is unadvised unless you are on a channel where all stations are using mutually non-conflicting timeslots on the same slot cycle length. Also, it is preferred to do timeslotting in a TNC rather than in client software like YAAC, because it will be more precisely aligned; YAAC only provides timeslotting capability to support TNCs (hardware or software) that do not natively support timeslotting themselves.
• Whether duplicate packets should be coalesced into a single transmission instead of retransmitted. Transmitting a burst of duplicates may be useful for modes like meteor-scatter, where only one or two of a burst of packets may get through, but is otherwise discouraged.

Note that this port type supports receiving from multiple KISS data ports over the same serial device, although it only transmits over data port #0. This supports the Byonics TinyTrak 4's GKRELAY command, which allows a GPS receiver connected to the TinyTrak (rather than to the computer running YAAC) to forward GPS sentences over the same cable used to send and receive APRS/AX.25 packets.

The "Test Port" button provides a means of verifying that you have connected to the correct place; it opens a terminal window connected to the configured serial port so that you can manually test the TNC for the desired operation. To complete testing, close the terminal window.

Once you have the settings the way you want them, click OK. Ensure that the TNC is connected to the port before you click OK. At that time, the port will issue commands to the TNC to put it in KISS mode, and then wait for AX.25 packets to arrive.

If you want to create a Serial_TNC port on a new installation of YAAC using the -createport option, the port_description is of the format:

where comportname is the name of the serial port on your operating system, such as COM3 or /dev/ttyUSB0, and baudRate is the serial port speed; this must be specified even for USB devices that don't have a configurable baud rate. transmitEnabled is either "true" or "false" (without the quotes) depending on whether you want this port able to transmit packets. Any digipeatAlias specified here must also already be specified on the expert-mode configuration dialog's Digipeat tab. If the TNC is not KISS-only, a kiss-command expression (as described above) should be specified after the semicolon.