TT31 Transponder Installation Manual

TT31 Transponder Installation Manual

00455-00

5.7 Interface Details

18 June 2014

Issue AP

5.7.1 Power Input

The power supply can be 11-33 Volts DC; no voltage adjustment is required. Contacts 11 and 12 on the 24 way connector are both available as power inputs. This is for compatibility reasons only – internally the two are connected together, and in most installations only one need be connected to the power supply.

Use a 3 Amp or greater circuit breaker for power supply protection to the TT31.

5.7.2 Lighting Bus Input

The TT31 will adjust the brightness of the front panel switch lighting according to the voltage on the lighting bus input. Two lighting bus inputs are provided on the 24 way connector to accommodate aircraft with 14 Volt or 28 Volt lighting systems. When the lighting bus operates at 28 Volts, connect the bus input to contact 3, and leave contact 2 unconnected. When the lighting bus operates at 14

Volts, connect the bus input to contact 2. In this case contact 3 can be left unconnected, but for backwards compatibility may also be grounded instead with no effect.

If no lighting bus input is detected, the TT31 will automatically control the front panel lighting based on the ambient light sensor.

5.7.3 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 TT31 provides two styles of mutual suppression interface on the 24 way connector. The Suppress input on contact 9 is typically used in aircraft with simple DME systems and no other suppression requirements. It is an input only, and is active whenever the input is greater than approximately 5

Volts.

The Suppress I/O on contact 4 is an ARINC compatible suppression bus interface, which acts as both an input and an output. The TT31 will assert this signal when it is transmitting, and can be suppressed by other equipment that asserts the signal. The TT31 will drive approximately 24 Volts on the output

(independently of supply voltage), and will treat the input as active whenever the bus has greater than

10 Volts.

5.7.4 Serial Port Options

There are two RS232 serial input/output ports, one on the primary connector (pins 6 and 7) and one on the secondary connector (pins 2 and 3). The input sources can be an altitude encoder, air data computer, or GPS for ADS-B support. The output can be serial altitude data for baro-aided GPS devices, or TIS traffic for suitable display.

Note: although each input and output can be assigned separately, the line speed for each input and output pair can only be set together.

5.7.5 Altitude Inputs and Output

The TT31 can use either a parallel Gray code altitude input, or serial RS232 altitude input. The Gray code interface is on the 24 way connector, whereas the serial altitude can be configured to be on either of the two RS232 inputs. If the altitude encoder you are using offers both, we recommend using the

RS232 serial input. Serial formats allow a higher resolution altitude representation that can be used by

Mode S interrogations, whereas parallel Gray code format can only represent altitude to the nearest 100 feet. You must choose between serial or parallel formats – you should NOT connect both. If a parallel encoder is connected the TT31 will always use that as the altitude source even if a serial encoder is also connected.

The parallel encoder inputs are active when the voltage to ground is pulled below approximately 4

Volts. The TT31 includes internal isolation diodes which prevent the unit from pulling the encoder

Trig Avionics Limited

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