G900X/G950 Installation and Maintenance Manual – Pinouts
Page A-71
190-00719-00
Revision D
A.7.4 Altitude
Functions
Altitude functions with pin assignments are shown for reference since the altitude function is available in
the GTX 33. In the G900X/G950 system, altitude data is received from the GIA 63W in RS-232 format.
Parallel gray code altitude inputs are considered active if either the voltage to ground is < 1.9 V or the
resistance to ground is < 375
Ω
. These inputs are considered inactive if the voltage to ground is
11-33 VDC.
NOTES
The GTX 33 contains internal altitude code line isolation diodes to prevent
the unit from pulling the encoder lines to ground when the transponder is
turned off.
If two separate altitude encoders are connected to the GTX 33, one providing
parallel gray code and the other, serial data, the unit selects only one for use
at a time, with serial data input receiving the highest priority.
For altitude encoders 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 not both wiring connections.
Among the surveillance items the Mode S transponder will transmit to the ground stations and other
aircraft are altitude reporting in 25’ increments with the proper encoder. In order to report altitude in
25-foot increments the GTX 33 must receive altitude from suitable altitude reporting devices through
serial input connections. Altitude input to the GTX 33 received from parallel wire gray code encoders is
supplied to the unit in 100-foot increments and thus reported in 100-foot increments.
A.7.4.1 Altimeter Inputs
Pin Name
Connector
Pin
I/O
ALTITUDE D4
P3301
11 In
ALTITUDE A1
P3301
2 In
ALTITUDE A2
P3301
4 In
ALTITUDE A4
P3301
5 In
ALTITUDE B1
P3301
7 In
ALTITUDE B2
P3301
9 In
ALTITUDE B4
P3301
10 In
ALTITUDE C1
P3301
8 In
ALTITUDE C2
P3301
3 In
ALTITUDE C4
P3301
6 In
ALTITUDE COMMON
P3301
50 --
