Garmin GTX 330, GTXTM 330D TRANSPONDER INSTALLATION MANUAL
Brand: Garmin, Pages: 71
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Page 4-4 GTX 330 Installation Manual
4.4 Altitude Functions
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. Refer to Figures C-2 and C-3 for parallel gray code and Figure C-3 for serial data altitude
interconnections. Carefully check encoder input lines for correct connection after wiring is complete.
The GTX 330 contains internal altitude code line isolation diodes to
prevent the unit from pulling the encoder lines to ground when the
transponder is turned off.
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 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 330 must receive altitude from suitable altitude reporting devices through serial
input connections. Altitude input to the GTX 330 received from parallel wire gray code encoders is
supplied to the unit in 100 foot increments and thus reported in 100 foot increments.
4.4.1 Altimeter Inputs
Table 4-5. Encoded Altitude Pin Assignments
Pin Name Pin Number I/O
ALTITUDE D4 11 In
ALTITUDE A1 2 In
ALTITUDE A2 4 In
ALTITUDE A4 5 In
ALTITUDE B1 7 In
ALTITUDE B2 9 In
ALTITUDE B4 10 In
ALTITUDE C1 8 In
ALTITUDE C2 3 In
ALTITUDE C4 6 In
ALTITUDE COMMON 50 --
RS-232 IN 2 24 In
4.4.2 Altimeter Calibration and Checkout
Refer to Section 5.2.14 for the gray code altitude checkout.
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GTX 330 Installation Manual Page 4-5
4.4.3 Altimeter Interconnect, Dual GTX 330 Installation
Refer to Figure C-2 for dual GTX 330 gray code altimeter interconnections. A dual GTX 330 installation
can accept either parallel wire gray code altimeter input or RS-232 serial data input as shown in Figure
4-2. If transponder number 2 is a Garmin GTX 327, connect the RS-232 output from the altitude encoder
to J3271 pin 19 (refer to GTX 327 Transponder Installation Manual, P/N 190-00187-02).
Figure 4-2. Dual GTX 330, Single Encoder, Serial Input Connections
For complete dual installations containing two encoders, it is best to connect one encoder to each
4.4.4 Altimeter Selection Priority
The installer must be aware of the GTX 330 priority for selecting encoded altimeter interconnections.
The GTX 330 searches in this sequence for altitude, and stops when it finds a valid pressure altitude
Only approved devices may provide altitude to the GTX 330 in accordance with 14 CFR Part 91.217. In
addition, all altitude reporting devices installed in the aircraft must meet certification requirements of
14 CFR Part 91.413. The installer must select an altitude reporting device that is a certified altitude
source for the particular aircraft.
Altitude reporting equipment order of precedence:
1) ARINC 429 Air Data Computer (label 203, if configured W/ALT) (25’)
2) ARINC 429 EFIS (label 203, if configured W/ALT) (25’)
3) RS-232 Fuel/Air Data Computer (if configured W/ALT.) (25’)
4) Parallel wire Gray Code input (100’)
5) Shadin Altitude Serializer/Encoder (100’/25’)
6) Icarus Altitude Serializer/Encoder (100’/25’)
It is the installing agency’s responsibility to determine that the installed encoder is compatible with the
selected altitude reporting criteria, either 100’ or 25’. Refer to Section 5.2.8 and 5.2.9 for the altitude data
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Page 4-6 GTX 330 Installation Manual
4.5 Discrete Functions
4.5.1 Discrete Outputs
Table 4-6. Discrete Outputs Pin Assignments
Pin Name Pin Number I/O
ALTITUDE ALERT ANNUNCIATE* 19 Out
EXTERNAL SUPPRESSION I/O 31 In/Out
* This output is considered active if either the voltage to ground is < 1.9 V or the resistance to ground
is < 375 Ω. This output is considered inactive if the voltage to ground is 11-33 Vdc.
4.5.2 Discrete Inputs
Table 4-7. Discrete Inputs Pin Assignments
Pin Name Pin Number I/O
EXTERNAL IDENT SELECT* 12 In
EXTERNAL STANDBY SELECT* 13 In
SQUAT SWITCH IN 17 In
TIS CONNECT SELECT* 46 In
AUDIO MUTE SELECT* 47 In
* These 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.
EXTERNAL IDENT SELECT (remote IDENT) is a momentary input.
Refer to Figure C-4 for the squat switch interconnect and to Sections 5.2.10. and 5.2.15 for the squat
EXTERNAL STANDBY SELECT (remote STANDBY) is a momentary input used when two GTX 330
systems are installed in an aircraft. Refer to Figures C-2, C-4, C-6 and C-7 for the EXTERNAL
STANDBY SELECT interconnect and to Sections 5.2.15 for verifying external standby configuration.
When EXTERNAL STANDBY SELECT is grounded, ARINC 429 OUT PORT 1 remains active, while
PORT 2 is inactive.
When TIS CONNECT SELECT is inactive (“Standby” is displayed on the 400/500 Series units) the
GTX 330 logs onto TIS service when a momentary ground is applied to P3301-46. When TIS is active, a
momentary ground logs off of TIS service. Refer to Figures C-1, C-4, C-6 and C-8 for TIS CONNECT
SELECT connections and to Sections 5.2.2. and 5.2.3 for TIS configuration.
An AUDIO MUTE SELECT mute switch may be used to control TIS audio alerts. TIS (Traffic) Mute
must be clearly marked with MUTE ON/MUTE OFF or TIS Audio ON/Audio OFF labels. The muting
feature may be enabled through a Multi-Function display. In order to prevent inadvertent muting, the
status of muting must default to "Mute off" upon each power cycle. Refer to Figures C-1, C-4 and C-8
for AUDIO MUTE SELECT connections and to Sections 5.2.2. and 5.2.3. for AUDIO configuration.
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GTX 330 Installation Manual Page 4-7
4.6 Serial Data Electrical Characteristics
The GTX 330 can be configured to include GPS, Airdata, AHRS, EFIS/Airdata, and ADLP ARINC 429
inputs, functioning as an ARINC 429 data concentrator.
Since the Garmin 400/500 Series products have only two ARINC 429 input ports, the GTX 330 manages
support for several equipment interfaces. The GTX 330 has four ARINC 429 input ports, making it
capable of taking altitude, air data, heading, EFIS selected course and possible future features, and then
concentrating it on the ARINC 429 OUT 2 port. This line is then wired to an ARINC 429 input port on
the 400/500 Series products. TIS data is included on the same high-speed ARINC 429 bus.
Airborne Data Link Processor (ADLP) is reserved for future data link applications. ADLP requires an
ARINC 429 input and output. The ADLP interface allows the Mode S data link transponder to function
as a modem. An ADLP performs functions requiring sending and/or receiving data from ground sensors
via Mode S interrogations and replies.
The GTX 330 is currently FAA approved to display TIS traffic
information on Garmin 400/500 Series products only.
4.6.1 RS-232 Input/Output
Table 4-8. RS-232 Pin Assignments
Pin Name Pin Number I/O
RS-232 OUT 1 23 Out
RS-232 IN 1 22 In
RS-232 OUT 2 25 Out
RS-232 IN 2 24 In
The RS-232 outputs conform to EIA Standard RS-232C with an output voltage swing of at least ±5 V
when driving a standard RS-232 load. Refer to Figures 4-3, C-3, C-5 and C-8 for the RS-232 serial data
interconnect and to Sections 5.2.9 and 5.2.17 for RS-232 serial data configuration.
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Page 4-8 GTX 330 Installation Manual
4.6.2 RS-232 Input/Output, Software Update Connections
An optional RS-232 serial data connector may be installed in the aircraft for future software upgrades,
negating the need to remove the transponder from the panel. The connector can be mounted anywhere
convenient for access, such as under the instrument panel, on a remote avionics shelf or in the instrument
panel itself. Be sure to label the connector for Software Update. Do not include the Test Mode Select
switch in the aircraft. See Figure 4-3 for software update connections.
Figure 4-3. GTX 330, Software Update Connections
4.6.3 Aircraft with Both TIS and TCAS/TCAD Installed
Refer to Figure C-8 for wiring connections. If redundant traffic systems are desired in the aircraft, such
as TIS and TCAD/TCAS, both systems cannot be connected to the same 400/500 Series unit to display
traffic simultaneously. In a multiple traffic system/multiple 400/500 Series unit installation, connect
ARINC 429 CHANNEL 1 from the GTX 330 to only one of the 400/500 Series units and ARINC 429
CHANNEL 2 to the other 400/500 Series unit.
Connect the TIS CONNECT SELECT line from the GTX 330 to the 400/500 Series unit receiving TIS
data. The TCAD/TCAS system may now be connected to the second 400/500 Series unit.
Refer to Section 5 for configuration. Configure ARINC 429 output CHANNEL 1 for GARMIN W/TIS
and ARINC 429 output CHANNEL 2 for GARMIN. TIS is then enabled over CHANNEL 1 when the
GTX 330 is connected to a Garmin 400/500 Series unit through the ARINC 429 wiring.
All configured input data that is concentrated through the GTX 330 via ARINC 429 lines, is received in
the second 400/500 Series unit via ARINC 429 CHANNEL 2 while the GTX 330 is active. No data is
received over ARINC 429 CHANNEL 2 while the GTX 330 is in remote standby. (Remote standby is
usually used as part of a dual transponder installation.)