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Section 2.0 Operation
2.1 General:
The SSD-120(XX)A( )-RS series of altitude digitizer=s are designed to be
mounted within a pressurized or non-pressurized, but temperature controlled area
within aircraft operating up to 42,000 feet MSL. Usually remotely located, the
digitizer is fully automatic in operation. The parallel data output is controlled by
the transponder while the serial altitude data is transmitted asynchronously.
2.2 Operating Instructions:
Parallel Data:
power to the transponder and to the digitizer. In some installations the digitizer
will automatically be supplied power when the transponder is energized; in
others, power to the digitizer may be through a separate circuit breaker. If power
to the digitizer is provided directly from the aircraft=s avionics buss, follow the
power-up procedures recommended by the transponder manufacturer. All parallel
outputs will be pulled low for a 30 second self test at power up, then assume the
value for
the present input pressure. In some installations, the transponder controls the
digitizer by enabling and disabling its outputs. In other installations, the
digitizer=s output is not controlled by the transponder and is continuously enabled,
(Digitizer pin 6 is grounded.)
Serial Data
after the self-test/warm-up is complete. Strobing the parallel data output of the
digitizer will not affect the serial data transmission.
Place the transponder in mode AC@ , altitude reporting mode, and apply
The serial communication is fully automatic and transmission begins
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