GTX 330/330D Installation Manual 190-00207-02Page 4-4 Rev. U4.4 Altitude FunctionsParallel gray code altitude inputs are considered active if either the voltage to ground is < 1.9 V or theresistance to ground is < 375 . These inputs are considered inactive if the voltage to ground is 11-33 Vdc. Refer to Figure D-6 and Figure D-9 for parallel gray code and serial data altitudeinterconnections. Carefully check encoder input lines for correct connection after wiring is complete.NOTESThe GTX 330 contains internal altitude code line isolation diodes to prevent the unit frompulling the encoder lines to ground when the transponder is turned off.If two separate altitude encoders are connected to the GTX 330, one providing parallelgray code and the other, serial data, the unit selects only one for use at a time, with serialdata input receiving the highest priority.For altimeters that can be connected in both serial data and parallel gray code format,such as the Garmin GAE 43 (Garmin P/N 013-00066-00), select one or the other but notboth wiring connections.Among the surveillance items the Mode S transponder will transmit to the ground stations and otheraircraft are altitude reporting in 25-foot increments with the proper encoder. In order to report altitude in25-foot increments the GTX 330 must receive altitude from suitable altitude reporting devices throughserial input connections. Altitude input to the GTX 330 received from parallel wire gray code encoders issupplied to the unit in 100-foot increments and thus reported in 100-foot increments.4.4.1 Altimeter InputsTable 4-5 Encoded Altitude Pin AssignmentsPin Name Pin Number I/OALTITUDE D4 11 InALTITUDE A1 2 InALTITUDE A2 4 InALTITUDE A4 5 InALTITUDE B1 7 InALTITUDE B2 9 InALTITUDE B4 10 InALTITUDE C1 8 InALTITUDE C2 3 InALTITUDE C4 6 InALTITUDE COMMON 50 --RS-232 IN 2 24 In
