Garmin GTX327 Installation Manual

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GTX 327 Installation Manual Page 4-3190-00187-02 Revision K4.2 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 Ω. These inputs are considered inactive if the voltage to ground is11-33 Vdc. Refer to Figure C-3 for parallel gray code and serial data altitude interconnection. Carefullycheck encoder input lines for correct connection after wiring is complete.NOTESThe GTX 327 contains internal altitude code line isolation diodes to preventthe unit from pulling the encoder lines to ground when the transponder isturned off.If two separate altimeters are connected to the GTX 327, one providingparallel gray code and the other, serial data, the unit selects only one for useat a time, with serial data input receiving the highest priority.For altimeters that can be connected in both serial data and parallel gray codeformat, such as the Garmin GAE 43 (Garmin P/N 013-00066-00), select oneor the other but not both wiring connections.When connecting two GTX 327 transponders to a GPS, the unit can onlyreceive RS-232 serial data from one unit at a time. Use a DPDT switch forconnecting both serial data and External Standby Select. Refer to FigureC-3.4.2.1 Altimeter InputsTable 4-4. Encoded Altitude Pin AssignmentsPin Name Pin Number I/OALTITUDE D4 18 InALTITUDE A1 3 InALTITUDE A2 5 InALTITUDE A4 6 InALTITUDE B1 9 InALTITUDE B2 11 InALTITUDE B4 12 InALTITUDE C1 10 InALTITUDE C2 4 InALTITUDE C4 7 InALTITUDE COMMON SIGNAL GROUND 13 or 25* --RS-232 IN 2 19 In* Altitude Common may be connected to pin 13 or 25. See Note 10 on Figure C-1, and Note 7 onFigure C-2.