Altitude Functions - Garmin GTX327 Installation Manual

4.2

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 Figure C-3 for parallel gray code and serial data altitude interconnection. Carefully
check encoder input lines for correct connection after wiring is complete.
The GTX 327 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 altimeters are connected to the GTX 327, 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 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.
When connecting two GTX 327 transponders to a GPS, the unit can only
receive RS-232 serial data from one unit at a time. Use a DPDT switch for
connecting both serial data and External Standby Select. Refer to Figure
C-3.
4.2.1 Altimeter Inputs
Table 4-4. Encoded Altitude Pin Assignments
ALTITUDE COMMON SIGNAL GROUND
* Altitude Common may be connected to pin 13 or 25. See Note 10 on Figure C-1, and Note 7 on
Figure C-2.
GTX 327 Installation Manual
190-00187-02
NOTES
Pin Name
ALTITUDE D4
ALTITUDE A1
ALTITUDE A2
ALTITUDE A4
ALTITUDE B1
ALTITUDE B2
ALTITUDE B4
ALTITUDE C1
ALTITUDE C2
ALTITUDE C4
RS-232 IN 2
Pin Number
18
3
5
6
9
11
12
10
4
7
13 or 25*
19
I/O
In
In
In
In
In
In
In
In
In
In
--
In
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Revision K