Volume Control Multiplexer
The volume control multiplexer gets DC voltages from the remaining receiver volume controls.
The volume control multiplexer sequentially selects the inputs.
The data output goes to the REU as a control system data word.
This multiplexer operation stops when the switching multiplexer operates.
Select Circuits
A multiplexer selects each input in sequence for a given time. A clock in the REU increases the value of a counter(счетчик). This counter provides the select address for the two analog multiplexers.
Two multiplexers combine the data from all the switches and the controls. The scan inhibit circuits prevent the operation of one multiplexer output while the other scans.
Emergency Circuits
The REU gives power for the ACP. You lose ACP power when for these conditions:
REU has no power
ACP has the ALT selection.
These conditions occur when you lose power in the ACP:
The ALT/NORM relay has no power
The data line to the REU identifies MASK/BOOM selection
28 volts from MD&T goes through the ALT/NORM relay contacts to the VHF 1 mic selector switch lamp for the captain and observer, and VHF 2 mic selector switch lamp for the first officer.
General
These components send a push-to-talk (PTT) signal to the remote electronics unit (REU):
Audio control panel (ACP) radio-intercom PTT switches
Control wheel PTT switches
Remote mic switches
Hand microphone PTT switches.
Set the radio-intercom PTT switch on the ACP to R/T to send a PTT signal to a communications system. Set the switch to I/C to talk on the flight interphone system.
Push the remote mic switch on the glareshield to send a PTT signal to a communication system.
Set the control wheel PTT switch to MIC to send a PTT signal to a communications system. Set the switch to INT to talk on the flight interphone system.
The observer can only send a PTT from the hand microphone or ACP.
General
The remote electronics unit (REU) controls the communication between these:
Three flight deck stations
Service interphone
Flight interphone
All related electronics equipment.
The REU contains three identical station cards. The cards are for these crew members:
Captain
First officer
Observer.
The REU also has an audio accessory unit (AAU) card. The card contains circuitry for flight and service interphone, alert tone generation and various audio accessory functions.
REU cards process these signals:
REU inputs
REU outputs
AAU signals
Reu Inputs
Each station card in the REU receives audio from these sources:
Flight compartment microphones
Communication transceivers
Navigation receivers
Passenger address amplifier
AAU card aural alerts.
The station cards get control inputs from the audio control panels (ACPs) and microphone push-to-talk (PTT) switches.
The mux receiver, in the REU, sends a data clock to the ACP.
The ACP replies back with crew selected receiver audio, navigation signals, volume and particular transmitter.
The mux receiver responds to the crew inputs and sends control signals to the following circuits:
Receiver circuits
Mic/PTT select logic
Transmitter circuits
Speaker mute/volume logic.
The receiver circuits receive audio inputs from the communication and navigation systems, passenger address amplifier, service interphone and flight interphone. The circuits process the crew selected audio. The audio goes to summing amplifiers. The summing amplifiers send the audio to the speaker mute/volume logic circuits, CVR amplifier and headphone amplifier.
The mux receiver sends boom/mask and interphone PTT signals to the mic/PTT select logic. The mic/PTT select logic processes input microphone audio and PTT signals. It routes(направлять) the selection to the transmitter circuits. The mic/PTT select logic circuits process speaker mute signals and hot mic audio.
The transmitter circuits route the microphone audio and/or PTT to the selected communication system.
The speaker mute/volume logic circuits process flight compartment speaker muting and set the speaker volume to the level as commanded from the mux receiver.