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A

747-400
MAINTENANCE MANUAL

DIGITAL
INPUTS

DISCRETE INPUTS AIRCRAFT POWER

CDU PRINTER QAR ACARS CMC
AIRBORNE DATA LOADER
Data Management Unit (DMU) Functional Block Diagram Figure 3
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MAINTENANCE MANUAL

 3. Operation
_________
 A. Functional Description
 (1)  
Data Management Unit (Fig. 3)

 (a)  
The DMU is the major element of the ACMS providing data acquisition, data management, and data distribution functions.

 (b)  
Airplane information is generally received via ARINC 429 data buses to the DMU two controller modules and a discrete I/O module.

 (c)  
Each controller module is capable of receiving 24 ARINC digital inputs while the discrete I/O module can receive 30 discrete inputs.

 (d)  
The controller modules and the discrete I/O module send the digital inputs and discrete inputs to the processors.

 (e)  
The processors are CPU #1 and CPU #2. The CPU #1 receives the inputs and performs data scaling, formatting and validity testing of all input parameters.

 (f)  
The CPU #1 then downloads all input data to the CPU #2. The CPU #2 buffers all data and performs all logic decisions and processing required to control data flow to the output devices.

 (g)  
The CPU #2 downloads the airplane information to CDU, multi-input printer, ACARS, airborne data loader and QAR (if installed).

 (h)  
Both processors CPU #1 and CPU #2 have a self-test function and are independent from each other. They process input data as determined by the software.

 (2)  
Quick Access Recorder

 (a)  
The QAR records the digital data stream provided by the auxiliary output of the DMU on optical disk to permit the data to be extracted for ground processing.

 (b)  
When power is applied to the unit, the QAR interface circuitry receives and sends data from/to the DMU. The interface circuitry has the following functions: 1) QAR Frame Sync - Sync ensures subframe/frame registration

 with respect to the actual data blocks. 2) QAR Control - Control commands for the QAR such as user status request.
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MAINTENANCE MANUAL

B488 QUICK ACCESS RECORDER
WIRING PROVIDED TO FACILITATE INTERCHANGEABILITY
OF OPTICAL AND QUICK TAPE ACCESS RECORDER

1
Quick Access Recorder (QAR) Schematic Diagram Figure 4
E47261
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 3)  QAR Status - Output status information and provides data replay.
 4)  Playback - This is provided for the output of data to the DMU.
 5)  Tape Low - Signals when recording on the optical disk is at the limits of remaining recording time, remaining recording space, or percent of disk space remaining.
 (c)  
When the data is routed to the central processing unit (CPU), the CPU automatically performs a ROM and RAM selftest to check the validity of the input data. It stores the data in memory in readiness for retrieval. It also contains the software necessary to control the handling of data within the QAR.
　
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