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B. Decoder Encoder Units (DEU)
(1) Description
(Ref. Fig. 019)
(a)
General Two types of DEUs are used, type A 200RH and type B 300RH. The director transmits address coded data to all DEUs of one type, but only one DEU A responds. The addressed DEU serves as an interface between the encoded bus data and the connected cabin systems and components.
(b)
Common Functions Each DEU has specialized functions appropriate to the connected systems. Certain functions, however, are common to both types of DEU, as follows:
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the adaption of received data bus signals,
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the comparison of received addresses with wired DEU addresses,
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the processing of addressed commands and controls,
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the commands control the cabin system interface,
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the conversion of processed control data for initiation of the interface circuitry,
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the adaption of cabin system interface signals,
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the processing of inputs from cabin systems,
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the transmission of data at assigned intervals via the data bus,
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the fail passive for data bus transmission and reception in case of DEU failure,
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the fail passive for system interface in case of DEU failure,
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the transmission of status results to director,
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the short-circuit protection of discrete outputs,
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the activation of emergency mode with minimum power consumption,
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the conversion of preselected audio channel.
(c)
DEU Type A Functions The DEU A interfaces with these systems and components:
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the passenger address loudspeakers,
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the passenger call switches and lamps,
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the cabin illumination ballast units,
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the passenger lighted signs,
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the passenger reading lights. The DEU A has these specialized functions:
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a test of lamp current,
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a test of connected loudspeaker impedance and level,
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a frequency filtering according to bus commands.
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DEU - Physical Appearance
Figure 019
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(d)
DEU B Functions The DEU B interface with these components:
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the attendant handset,
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the attendant indication panels,
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the area call panels,
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the emergency slide bottle pressure sensors,
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the information signs,
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the emergency evacuation controls and indicators,
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the emergency lighting power supply units (EPSU),
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the additional attendant panel.
(e)
DEU Architecture (Ref. Fig. 020, 021) The circuitry of the two types of DEU consists of:
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the bus interface circuits,
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the power supply circuits,
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the system interface circuits,
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the gate array and oscillator.
(f)
CIDS Data Bus Interface Discrete input data from the cabin systems, (DEU BITE status, and DEU B audio input data) is passed to the interface via the internal bus. The interface serializes the parallel data and transmits it along the CIDS data-bus according to the CIDS data-bus protocol. Each DEU data-bus interface-module contains time-out circuitry. This time-out circuitry prevents extended bus transmission when there is a faulty DEU. The data-bus interface buffering ensures that a faulty DEU cannot degrade the CIDS data-bus performance. A through-connection (in the DEU mounting-bracket) provides for the connection of the next length of data bus shielded twisted pair cable.
(g)
Power Supply Module The DEU power-supply module derives the internal supply voltages from the 28V DC service and essential busses. The essential bus supplies circuitry necessary for passenger address operation, interphone operation, and emergency evacuation signalling and control. Service bus-power supplies all remaining circuitry. In an aircraft emergency, the service bus disconnects and removes the load due to passenger lighted signs and seat row numbering lights. When the director detects an aircraft emergency, it deactivates the topline cut-off relay 106RH as long as no PA announcements are made. This disconnects all DEUs A from the essential bus. In the absence of essential power, the DEUs automatically switch over to total service-bus operation. The power supply module safeguards the connected power lines against DEU failure.
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