The MU transmits data to the multi-input cockpit printer.
 The printer is not dedicated only to the ACARS. The MU can buffer data
 printing when the printer is busy with another system.

 D. ACARS MU/VHF 3 interface
 The MU receives uplinks and transmits downlinks through the VHF 3 transceiver. The VHF 3 transceiver is not dedicated only to ACARS, it is also used as a back-up of the VHF 1 or VHF 2. Each of the three RMPs is connected to the remote voice/data select discrete-input of the MU. This discrete can apply on this input a voice/data mode transfer command. The MU is connected to the key event discrete-output from the VHF 3 which indicates that the push-to-talk input of the VHF 3 is activated. The MU can use this information to automatically resume control of the transceiver after a voice conversation through VHF 3 (the MU can resume control of the VHF 3 after a time interval of 2 minutes has elapsed since the last VHF 3 push-to-talk activation).
 E. Interface with the ground network
 The airline can exchange data with its aircraft through a ground network
 which is managed by four world service providers:
 These providers are:

 -ARINC, in the USA

 -CANADIAN, in Canada

 -JAPANESE, in Japan

 -SITA, in the other regions.
 In this ground network, each service provider is responsible for its own
 network.
 The networks are interconnected, therefore the data is transferred over
 any network.
 The aircraft can be in liaison with the network through the VHF.
 On the network, it is possible to communicate through two types of
 transmission:

 (1) CATEGORY A The aircraft can transmit or receive data to or from all the VHF transceivers which are in the line of sight of the aircraft.
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 (2) CATEGORY B The aircraft can transmit or receive data to or from one VHF transceiver only. It selects the VHF transceiver with which it wants to communicate after reception of a squitter. On the ground, each service provider works on a special frequency:
 -131,55 MHz for the ARINC network

 -131,475 MHz for the CANADIAN network

 -131,450 MHz for the JAPANESE network

 -131,725 MHz for the SITA network.
 In order to communicate, the ACARS MU tunes the frequency through a
 frequency management algorithm.

 6. Operation
_________
 A. Connection with the DMU
 (1)
 Each report generated by the DMU can be programmed individually for transmission to the ACARS MU either automatically or manually.

 (2)
 The ACARS MU can also require generation and transmission of any report by the DMU.

 (3)
 The ACARS MU can send information to the DMU when each report has been duly transmitted to the ground.

 (4)
 All these functions are described with their operational use related to the DMU in the ATA 31-36.

 B. Connection with the CFDIU
 (1)
 All the fault messages and all the warnings recorded by the CFDIU can be transmitted automatically to the ACARS MU as soon as the CFDIU receives them from a system or a Flight Warning Computer.

 (2)
 The CFDIU can transmit the post-flight report automatically to the ACARS MU at the end of the flight. This report can also be transmitted to the ACARS MU manually.

 (3)
 Any page displayed by the CFDIU on one MCDU, which is a resultant of the dialogue in menu mode between the CFDIU and a system, can be transmitted manually to the ACARS MU.

 (4)
 Each function is rendered operational or not depending on the message transmitted by the ACARS MU to the CFDIU. These functions are described with their operational use related to the CFDIU in the ATA 31-32.

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 (5) The ACARS MU (and all the systems linked to the CFDIU) is provided by the CFDIU with the following:
 -Aircraft identification (tail number)
 -Flight number
 -Identifications of departure and destination airports
 -Date
 -Time
 -Flight phase
 -Installed optional systems.
 C. Connection with the FMGCs
 (1)
 The ACARS MU is linked to the FMGC1 and 2.

 (2)
 The FMGCs transmit the following messages to the ACARS MU either automatically or manually:

 -
Request for flight plan initialization

 -
Request for wind messages

 -Pre-flight report
 -In-flight report
 -Post-flight report.
　
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