-
The display of the RMP which has generated the command is modified immediately, as follows, until control is taken over by the ACARS MU:

 *
 Dashes appear in the ACTIVE display

 *
 The frequency which was in the ACTIVE display appears in the STBY/CRS display window

 -
The display of the other RMPs in VHF3 mode remains unchanged until control is taken over by the ACARS MU.

 -When the ACARS MU takes the control again (by changing the state of the port select discrete to ground), the display of the RMPs in VHF3 mode is modified as follows :
 *
 For the RMP which has generated the command the dashes in the ACTIVE display window are replaced by the ACARS indication.

 *
 For the other RMPs, the ACARS indication appears in the ACTIVE display window. The frequency which was in the ACTIVE display window appears in the STBY/CRS display window.

 NOTE : Time elapsed between command initiation and the taking
____ of control by the ACARS MU is very short.
 (b) Control of VHF3 frequency through ACARS MU only (in radio or DATA mode) The pilots can modify the frequency or the operating mode (radio or DATA mode) through the MCDU.
 G. Connection with the MCDUs
 (1)
 The ACARS MU is interfaced with two or three MCDUs

 (2)
 The MCDUs enable:

 (a)
 The display of data generated by the ACARS MU from data transmitted by the ground or by peripheral computers (DMU, CFDIU, FWC1, SDAC1).

 (b)
 The selection of the various functions of the ACARS MU.

 (c)
 The entry of data or text by the crew.

 (3)
 Dialogue between one MCDU and the ACARS MU is initiated when ACARS is selected on the MCDU menu. This dialogue is performed according to the protocol specific to the exchanges of data with the MCDUs, the same protocol being used for the dialogues between the MCDUs and the following: FMGCs, CFDIU and DMU (Ref. ATA 22-82).

R 1EFF : 001-049, 051-099, 101-105, 1 23-24-00Page 16 1 1 May 01/05 1 1 1CES 1

 H. Connection with the Printer
 (1)
 The ACARS MU is linked to the printer. This enables to print:

 -
The data generated by the ACARS MU from data transmitted by the ground and by peripheral computers,

 -
The data entered by the crew through the MCDUs.

 (2)
 The data are transmitted to the printer by the ACARS MU according to a specific protocol which is also used by the other computers operating in conjunction with the printer (Ref. ATA 31-35).

 J. Data Exchange between Aircraft and Ground Network
 (1) Data coding The data exchanged between the ACARS MU and the VHF3 transceiver are coded by 1200 and 2400 Hz tones
R  (Ref. Fig. 006) A zero-bit is coded:
 -
By a positive half period of 1200 Hz when it is the first of a string of zero-bits (even if the string only comprises this single bit).

 -
By a 2400 Hz period starting by the negative half period when this

 is not the case.
 A one-bit is coded:

 -
by a negative half period of 1200 Hz when it is the first of a string of one-bits (even if the string only comprises this single bit).

 -
by a 2400 Hz period starting by the positive half period when this

 is not the case. The signal transmitted by the ACARS MU to the VHF3 modulates the VHF radio signal sent to the ground. Conversely, the signal transmitted by the VHF3 to the ACARS MU is obtained after demodulation of the radio signal from the ground. The result of this coding is that the transmission rate is 2400 bits per second from aircraft to ground and vice versa. The transmitted data are characters from the ISO alphabet No.5 except the block check sequence field at the end of transmission.
R  (Ref. Fig. 007)
 (2) Message format The format of the messages exchanged between the ground and the aircraft is as follows (in the transmission order):
R 1EFF : 001-049, 051-099, 101-105, 1 23-24-00Page 17 1 1 May 01/05 1 1 1CES 1

R  ACARS - Data Coding Figure 006 
R 1EFF : 1 1 1CES  001-049, 051-099, 101-105,  1 111 23-24-00 Page 18 May 01/05

 ACARS - ISO Alphabet No.5 R Figure 007
R 1EFF : 001-049, 051-099, 101-105, 1 23-24-00Page 19 1 1 May 01/05 1 1 1CES 1

 Pre-key (16 characters)
 Bit synchro (2 characters)
 Character synchro (2 characters)
 Start of heading (1 character)
 Mode (1 character)
 Address (7 characters)
 Technical acknowledgement (1 character)
 Label (2 characters)
　
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