User's Guide
Page 24
The GDL 39 has a pass-through (such as older products like the GPSMap 396/496). Some display devices do not support serial pass-through serial connection so a serial device can be connected to prevent unintentional connections. C Figure 3-6 Serial Pass-Through Connection NOTE: If the external serial device is not used, TxA and RxA can be left unconnected. 3-6 Garmin GDL 39 Portable ADS-B and GPS Receiver User's Guide 190-11110-00 Rev. NOTE: Secure unused wires to a display device that has a single serial connection.
The GDL 39 has a pass-through (such as older products like the GPSMap 396/496). Some display devices do not support serial pass-through serial connection so a serial device can be connected to prevent unintentional connections. C Figure 3-6 Serial Pass-Through Connection NOTE: If the external serial device is not used, TxA and RxA can be left unconnected. 3-6 Garmin GDL 39 Portable ADS-B and GPS Receiver User's Guide 190-11110-00 Rev. NOTE: Secure unused wires to a display device that has a single serial connection.