INSTALLATION MANUAL
CMA-5024 GLSSU
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without prior written permission by CMC Electronics Inc.
Page A.7
November 21, 2008
For X-Talk connections in a triple installation (Left/Center/Right units), interconnect Left
& Right units using the opposite X-Talk #1 inputs, Center unit outputs to the Left and
Right X-Talk #2 inputs, Left unit outputs to the Center X-Talk #1 input, and Right unit
outputs to the Center X-Talk #2 input.
CAUTION: The #1 and #2 DME and ILS input busses to the GLSSU must carry identical data
streams. In other words, connect the two DME/ILS inputs of the GLSSU to the outputs
from the same DME/ILS instrument. The inputs are treated independently when the HIS
source is ILS but only one automatically selected active input is used when the HIS
source is GLS.
CAUTION: The DADS/FMS input busses will accept only ARINC 419 DADS data inputs if the DADS
419/429 Select input discrete is set to the "419" state (grounded).
Notes: For SBAS Approaches, the HIS in the GLSSU will accept the DME/ILS data only from
either input bus #1 or #2 and automatically switch to the other (from #1 to #2 or vice
versa) when no activity is detected on the currently selected bus. Thus the data streams
to these two inputs must originate from the same DME/ILS instrument. In addition, the
HIS expects that the DME instrument outputs the data in blocs starting/ending with the
Frequency label (label 035); refer to the HIS description in subsection F in section I.
1.2.4 ARINC 429 INPUT DATA RATES
The GLSSU detects automatically the input data rate, either high speed (100 KB/S nominal) or low-
speed (12.5 KB/S nominal) on inputs that accept both speeds. It trains itself after each self-test (upon
power-up or initiated manually) on the first received data words and retains this speed until the next
self-test. The speed determination requires reception of labels at a rate of at least once per second for
up to 5 seconds. Data will not be accepted until the speed has been determined.
NOTE: Due to the training time, the GLSSU may miss the first few received input data words.
This is harmless in operation, but it may be confusing when bench-testing.
1.2.5 ARINC 429 INPUT PRIORITY
When ARINC 419/429 data is present with the SSM equal to Normal on both the primary (#1) and
secondary (#2) buses, the GLSSU gives priority to the data on the primary bus. Note that priority is
applicable only when data is received in continuously; for example, approach selection or burst labels
like Set Altitude (label 040) are processed on a first come first served basis.
1.2.6 ARINC 429 INPUT DATA FORMAT
The GLSSU accepts the ARINC data labels listed in Figures A-2 to A.11 below, respectively for the
IRS/FMS, FMS/DADS, X-Talk, OMS, GP/DIFF, Data Loader, Freq/Function Data Source, DME and ILS
input busses. The same notes apply to the all figures. For the format of the data labels, refer to
Appendix C where the note (h) applies or else refer to the standard ARINC 743A characteristic.
The ARINC 429 Broadcast Message Protocol complies with the ARINC 755-3, section 7.2.6, for
transferring FAS Data. The application message transmission must be a continuous transmission of
ARINC 429 labels and must terminate when the message block is complete. The application data
transmissions must be comprised of one or multiple concatenated message blocks. Each message
block must consist of a Message Header, a variable length Message and a CRC. Each message block
must contain a CRC, which will be used to validate the data.
The document reference is online, please check the correspondence between the online documentation and the printed version.
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