Trans-Cal SSD120-N-RS5, Owners & Installation Manual, Page: 11 / 57

Section 2.0 Operation
2.1 General
The SSD-120(XX)N( )-RS5 series of altitude digitizers 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. (Half duplex, talk only. Full duplex in calibration and
configuration modes only.)
2.2 Operating Instructions
Parallel Data:
Place the transponder in mode “C”, altitude-reporting mode, and apply 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 self-test (3 seconds) at power up,
then assume the value for the present input pressure. Note, a short the warm-up time may
affect the actual data enable time. At 0ºC a 30 second period is required before the data
will enable. In some installations, the transponder controls the digitizer by enabling and
disabling its output. In other installations, the digitizer’s output is not controlled by the
transponder and is continuously enabled, (Digitizer pin 6 is grounded.)
Serial
Data
The serial communication is fully automatic and transmission begins after the self-test is
complete. Strobing (pin 6) the parallel ICAO altitude data output of the digitizer will not
affect the serial data transmission.
SERI AL DATA
RECEPTACLE DA-15S
PARALLEL DATA AND POWER
CONNECTOR DA-15P
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