There is a bi-directional RS485 data bus between the video tape reproducer and the video system control unit.
The video system control unit sends commands to the video tape reproducer to control the operation of the video tape reproducer.
The video tape reproducer sends status information to the video system control unit.
The video tape reproducer plays video programs. The video tape reproducer sends the video and three separate audio signals to the video system control unit.
Passenger Address System
The passenger address system sends a discrete signal to the video system control unit. The discrete is a ground when there is a push-to-talk (PTT) from any one of these sources:
* Flight crew (priority 1)
* Cabin attendants (priority 2)
* Tape reproducer for pre-recorded announcements (priority 3).
When the passenger address discrete is a ground, the video system control unit tells the video tape reproducers to pause.
Passenger Oxygen System
When the passenger oxygen comes on, the oxygen indication relay energizes. This causes the VSCU to shut down. When the VSCU is off, the video tape reproducers stop and the video monitors shut down.
The proximity switch electronics unit (PSEU) provides discretes which the VSCU uses to identify the phase of a flight. The VSCU can start or stop video programs when the airplane gets to a specific phase of flight.
The PSEU provides these discretes to the VSCU:
* Nose gear discrete - set when the nose landing gear is down and locked
* Air/ground discrete - set when the airplane is on the ground
* Parking brake discrete - set when the parking brake is set and the airplane is on the ground.
The video system control unit has audio outputs for two kinds of programs, entertainment programs and announcement programs.
The video system control unit can send audio from three programs to the audio multiplexer for the entertainment of the passengers. The passengers select the program on the passenger control unit which is part of the PES-audio. Each program has two audio outputs. This lets the passengers listen to the programs in more than one language.
The video system control unit sends audio to the passenger address (PA) amplifier for programs which are broadcast to all passengers. The audio goes through the video system relay 1.
When the announcement plays, the video system control unit sends a discrete signal (PA KEY) to the PA amplifier. The PA amplifier uses this signal to prioritize the audio inputs. The announcement audio has priority 3.
The PA KEY goes to the PES-audio to stop the audio entertainment player.
The video system control unit (VSCU) sends video signals and control signals to the video distribution units (VDUs). The VDUs send video signals to the video monitors.
The VSCU receives signals to monitor the status of the video monitors.
The VSCU sends three video signals to the first VDU in the forward and aft sections. The VDU sends the video signals on to the next VDU in the section.
The last VDU in the section has a termination plug. The termination plug provides a 50-ohm termination for each video signal.
Each VDU sends one of the three video signals to the video monitors.
The VSCU sends control signals to the VDUs in the forward and aft sections. The data goes to the first VDU in the section. The VDU sends the data to the next VDU in the section.
The VSCU and VDUs use bi-directional data buses for data transfer.
The control signals tell the VDU when to apply power to the video monitors. The control signals also tell the VDU which one of the three video signals to send to the video monitors.
The video monitors tell the VDUs when the video monitor is on.
The VDUs send the status of the video monitors to the VSCU.
The digital interface unit (DIU) receives commands to control the operation of airshow.
The DIU receives airplane flight information from other systems.
The DIU sends video signals to the video system control unit.
The video system control unit (VSCU) sends commands to the DIU. The DIU and VSCU communicate with each other with the RS485 data bus.