Hardware Serial Port

The Hardware Serial Port (HSP) is a simple two-transistor circuit that allows multiplexing a single PC serial port to get data from both a serial-connected TNC and a serial-connected GPS unit.

With one of these circuits connected to the PC serial port, Xastir will use the DTR (Data Terminal Ready) pin of the serial port to toggle between whether it's listening to the TNC or the GPS, and farm the data it receives to its database as appropriate.

It's an old-fashioned solution for using old-fashioned equipment.

If you want to build one, you can check out this circuit diagram.

Some more involved and updated circuits for doing the same thing may be found here.