User's Manual

SYSTEM DESCRIPTION AND INSTALLATION MANUAL
T
3
CAS/Part No.9005000
Display dimming is controlled from several inputs consisting of an internal light
sensor mounted on the bezel of the LRU, a remote light sensor, and the aircraft
dimming bus. The display is dimmed by varying the brightness of the LCD panel
backlighting.
(9) Software Considerations
VSI/TRA software is developed to a DO-178A category of Level ll (essential).
The software continually monitors and displays vertical speed and TCAS
information. Output discretes supply user components with the status of the LRU.
TCAS valid indicates that the LRU is displaying valid TCAS information. On the
ACSS 55-pin version, VSI valid indicates that the LRU is displaying valid vertical
speed information. This is needed to support the bootstrap feature, which is
exclusive to the 55-pin version of the VSI/TRA display.
(10) Built-In-Test Equipment (BITE) and Self-Test Capability
The LRU has input discretes that allow a calibration and test program to be run.
This mode allows the display to be adjusted and various diagnostic tests to be
performed. These tests and adjustments can only be done in a shop on a
dedicated test fixture.
When the LRU application program is operating in the aircraft, the background
loop continuously monitors the power supply status, the ROM integrity, and the
analog range limits. A failure results in the setting of bad status output discretes.
A cold start will continuously be attempted until the LRU passes the built-in-test.
There is a dedicated self-test input for both versions of the VSI/TRA Display.
When this pin is activated, the unit will display symbology that aids in the
detection of unit faults.
Pub. No. 8600200-001, Revision 004
34-45-29
1-72
04 Nov 2014
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