TT21/TT22 Transponder Installation Manual
22 August 2017
00560-00
AP
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16
Trig Avionics Limited
power connections. Reversing the power and ground inputs to the
transponder will destroy it. Check wiring before applying power.
5.6.2
TMAP Bus
TMAP is a Trig proprietary bus based on RS485 signalling. It provides a bi-
directional interface between the transponder and the control head. Each
TMAP interface comprises a balanced pair of signals, called A and B, both of
which must be connected for communication to work.
There are two sets of TMAP pins on the TT21/TT22, TMAP1 A and B, and
TMAP2 A and B. This is to support future installation wiring options. The
two sets are identical, and either pair (TMAP1 or TMAP2) may be used to
connect to the control head.
5.6.3
Power On
The TT21/TT22 power supply can be directly controlled by this discrete input.
The input is active low, so that the TT21/TT22 will power up whenever the
input is held low. This signal is intended to connect to the TC20 Remote ON
output.
5.6.4
Controller Power
The TC20 controller does not connect to aircraft power – it receives power
from the TT21/TT22 using this output. The TT21/TT22 provides 6.5 Volts to
the TC20. This output includes short circuit protection, and no fuse is required
between the TT21/TT22 and the TC20.
5.6.5
Mutual Suppression
Mutual suppression allows two or more transmitters on adjacent frequencies to
inhibit the other transmitters when one is active to limit the interference effects.
It is commonly used between transponders and DME systems, and between
transponders and collision avoidance systems.
The Suppress I/O on pin 18 is an ARINC compatible suppression bus interface,
which acts as both an input and an output. The TT21/TT22 will assert this
