Squat Switch Input; Ident Switch Input; External Standby Input; Audio Output - Honeywell BendixKing KT 74 Installation Manual

The KT 74 includes a serial altitude output which repeats the altitude
received on the encoded input (either parallel or serial) for connection to a
GPS or other equipment. The serial output supplies RS232 output levels, and
runs at 9,600 bps, no parity. The output format is always
"Icarus/Trimble/Garmin" format. If the altitude source is a parallel encoder,
the serial output is reported every 0.5 seconds; if the source is a serial
encoder, the output simply repeats the input reports, each report delayed by
up to 10 milliseconds from the corresponding input report.

2.6.5 Squat Switch Input

The Squat switch input allows the transponder to automatically switch
between Airborne and Ground modes of operation. The squat switch will also
automatically start and stop the flight timer. The input will be asserted when
the voltage to ground is pulled below approximately 4 volts. The operating
mode of the squat switch can be programmed during setup to allow for active
low or active high logical behavior. For aircraft with no squat switch this input
should be left open circuit, and the setup mode programmed for "Not
Connected".

2.6.6 Ident Switch Input

The Ident switch input, on the 24-way connector, allows the IDENT function
to be selected using a remote switch. The input is active low, and will be
asserted when the voltage to ground is pulled below approximately 4 volts.

2.6.7 External Standby Input

This input, when held low, places the transponder in Standby mode. It should
be used to switch between transponders in an installation with two
transponders. The input is active low, and will be asserted when the voltage
to ground is pulled below approximately 4 volts.

2.6.8 Audio Output

The audio output is on the 12-way secondary connector. The audio output is
a balanced (two wire) audio output that can be connected to an unswitched
input on the aircraft audio panel. Audio output is up to 10 volts peak-to-peak
across the pair when driving a 600-ohm load. Actual level can be adjusted at
installation. Refer to Section 2.
NOTE: The audio pair is not a true transformer balanced output – both pins are
actively driven. If the audio panel input is single-ended, then only one of the
output pins should be used, together with a local ground pin – the other audio
output should be left floating.
The audio output carries the traffic alert messages for TIS-A, and the altitude
audio annunciator used by the altitude monitor function.
© Honeywell International Inc. Do not copy without express permission of Honeywell.
INSTALLATION MANUAL
89000007
Page 2-11
15 Nov 2013