*
Power interrupt processing.

The initialization sub-function does software installation checks on the DCMF software components during initialization. These components are the:
*
Operational program configuration (OPC)

*
Operational program software (OPS)

*
Airline modifiable information (AMI).

Power interrupt processing reacts to primary power system interrupts in different ways. The reaction depends on the length of the interrupt and if the airplane is on the ground or in the air. The power interrupt groups are:
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DCMS -DCMF FUNCTIONAL DESCRIPTION

* Short term power interrupt (<500 ms)
*
Warm start (主 500 ms and < 5 s)

*
Cold start (主 5 s and airplane in air)

*
Complete power loss.

BITE Sub-function
The DCMF BITE sub-function monitors the DCMF in the left and right CPM/Comm and the related hardware units use that the DCMFs use. The related hardware units that the DCMFs use are, the OLAN circuit card assembly (CCA) and the VHF modem in each CPM/Comm module. When the system first gets power, the power-up BITE test makes sure that the DCMF works correctly. During normal operation, the BITE continuously monitors the condition of the DCMF for redundancy management.
Redundancy Management Sub-function
The redundancy management sub-function of the DCMF does these four things:
*
DCMF selection as primary at power-up

*
Primary to secondary DCMF transfer

*
External hardware monitors

*
Datalink monitors.

The redundancy management function makes sure that one of the two DCMFs is primary and one is secondary. The primary DCMF does:
*
All air/ground communications

*
Maintenance of AVLAN connections to AIMS functions within its cabinet

*
Monitors condition and status of the secondary DCMF.

The secondary DCMF does the same functions as the primary, but it does not handle air/ground communications.
The secondary DCMF takes over for the primary DCMF if it fails or if the flight crew changes the default VHF communications transceiver. The secondary DCMF monitors the intercabinet status messages from the primary DCMF. The primary DCMF uses the results of the monitors and other conditions to change to the secondary DCMF. The DCMF monitors this hardware for correct operation:
*
Left, center, and right RTPs

*
Center and right VHF comm xcvrs

*
The SDU

*
Flight compartment printer.

The DCMF monitors the condition of the VHF and SATCOM datalinks. The DCMF sends messages to the PDF for flight crew notification when the condition of the VHF or SATCOM systems change.
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777 AIRCRAFT MAINTENANCE MANUAL

DCMS -DCMF FUNCTIONAL DESCRIPTION

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DCMS -FUNCTIONAL DESCRIPTION -ACARS DATALINK SUB-FUNCTION

General
The ACARS datalink sub-function requires air/ground communications. The VHF or SATCOM path of the DCMF does the air/ground communications.
The AIMS functions send downlink data to the ACARS datalink sub-function for delivery to the ground service provider (GSP). Usually, the AIMS function keeps a copy of the data until the ACARS datalink sub-function sends a notice of successful delivery to the GSP. The ACARS datalink sub-function also tells the AIMS function that sends the data of unsuccessful downlink attempts.
If the air/ground link with the GSP is broken, the ACARS datalink sub-function sends any data waiting for the downlink back to the sending function. The ACARS datalink sub-function rejects all downlink attempts until it restores a link.
The ACARS datalink sub-function sends uplink messages to the datalink functions. If all of the messages arrive successfully, the ACARS datalink sub-function supplies an indication.
These are the parts of the ACARS datalink sub-function:
*
Communication Program Interface (CPI)

*
ACARS router

*
Redundancy management

*
Williamsburg protocol

*
ACARS air/ground protocol

*
RTP interface

*
Modem.

Communications Program Interface
The communications program interface (CPI) supplies a link between the DCMF and AIMS internal functions.
ACARS Router
The ACARS router routes messages for both downlinks and uplinks. For downlinks, the ACARS router receives data, through the CPI and sends the data to the GSP through VHF or SATCOM. The ACARS router uses these to set the downlink path:
　
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