190-01499-02
GTX 3x5 TSO Installation Manual
Rev. 1
Page 5-5
5.6 Altitude Inputs
The GTX 3x5 can use pressure altitude inputs from several different sources, using the gray code inputs,
an RS-232 serial input, an ARINC 429 input, or the optional pressure sensor module (Garmin P/N 011-
03080-00). If multiple altitude sources are connected, the GTX 3x5 will prioritize them as follows:
1. Optional pressure sensor module
2. ARINC 429 input
3. RS-232 input
4. Parallel Gray code input
Among the surveillance items that the Mode S transponder (GTX 335 and GTX 345) will transmit to the
ground stations and other aircraft are altitude reporting in 25 foot resolution with the proper encoder. In
order to report altitude in 25 foot resolution, the GTX 3x5 must receive altitude from a suitable altitude
reporting device through the serial inputs or from the optional pressure sensor module. A parallel Gray
code encoder provides altitude in 100 foot resolution.
For altimeters that can be connected with both a serial interface and the parallel Gray code input, such as
the Garmin GAE 43 (P/N 013-00066-00), connect one or the other interfaces, but not both.
5.6.1 Pressure Sensor Module
The optional pressure sensor module (Garmin P/N 011-03080-00) can be used for the GTX 3x5 pressure
altitude input.
The pressure sensor module uses the same interface as the configuration module and also includes the
configuration module functionality. See section ??.
