Label 172 CMU Subsystem Identification - Bit Definition

Bit  Definition 
1-8  Label 172 (ID) 
9-16  System Address Label 304 (00100011) 
17-29  Spare = 0 
30-31  SSM 
32  Parity 

LRU Interconnect Status

CMU provides a maintenance screen that displays which LRUs are active. The definition of active is that the specific device is broadcasting an ARINC 429 data to CMU as expected. 
ACTIVE or INACTIVE indicates activity of the LRU.
NOT INSTALLED indicates the LRU is not installed based on the system configuration.
NO 429 Data indicates the LRU is installed but no 429 broadcast words are expected.
LRU Status

NOT INSTALLED
LRU not installed according to a/c configuration broadcast word, CMU application or defined in ACARS database
INACTIVE
ARINC 429 data present but no parameters are selected for use by ACARS CMU
ACTIVE
Selected ARINC 429 data present on bus
NO 429 DATA
LRU is installed but no ARINC 429 broadcast words on bus.

Discrete Status

CMU provides a maintenance screen that displays the CMU discrete input and output status and updated at 1 second intervals.

1 = Open Circuit 0 = Ground
Discrete Status

View Status of CMU Discrete Inputs and Outputs

This is number 1 of 5 pages (dependent
upon aircraft type).
Status is updated at 1 second intervals.
“1” represents Open Circuit.
“0” represents Ground.

Data Link Test

Data Link Test is not required for normal maintenance activity. It should be noted that VHF Link Test may fail although there is nothing wrong with CMU. This is generally a result of poor VHF coverage of the Aircraft.
Selecting VHF Link Test will result in CMU sending a downlink to ground. If an acknowledgment is received from ground, CMU will display PASS for 5 seconds. If not, CMU will display FAIL for 5 seconds.
If an SDU unit is installed on the aircraft, similar test can be performed by selecting SATLINK on screen.
Test Menu 1/2
VHF & SAT LINK

Communication link test with RGS or Satellite. Success determined by Acknowledgement of ground Station or Satellite. When Link Test is initiated, prompt changes to TEST indicating active, then to PASS when Acknowledgement received or FAIL when test timer expires.
PRINTER
Print all possible characters.
MCDU
Display all possible characters.
RAM TEST
Test memory of ACARS CMU.
COMM AUDIT
Access to communication audit page.

LRU Interface Test

LRU Interface Test allows user to perform a SOLO word loop back test on LRU(s) using Williamsburg (Bit Oriented) Protocol to perform file transfer.
　
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