Connector FMGC Figure 006 
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 It is therefore maintained in the event of aircraft power cutoff (Ref. para. (3)).
 (c) The FM CPU board fulfills the flight management tasks. The board is equipped with a memory module. It also includes the shared memory for dialogue with the FG part. Upon energization a test program is activated if the aircraft is on the ground.
 (2)
 Guidance function

 (a)
 Digital part This part uses two processors : the INNER LOOP processor and the GUIDANCE COMMAND processor. The dialogue between the two processors is performed through a shared memory. The correct running of the program is checked by a watchdog. The result is directly taken into account in the system engagement hardwired logic on the EXTENSION COM board. Safety tests are activated at power-up when the aircraft is on the ground. The guidance part, command channel, is integrated on three boards:

 -
a ILCPU (Inner Loop CPU)

 -
a CPU AFS

 -an EXTENSION COM
 -ARINC acquisition for the Flight Management (FM) and guidance functions either directly or through the INNER LOOP board
 -dialogue with the FM part
 -
computation of the operational logic

 -
computation of the AP, FD and A/THR outer loop signals and transmission of these signals to the INNER LOOP processor

 -transmission of the flight management parameters on the ARINC bus C
 -monitoring of the alpha floor detection

 (b)
 Hardwired logic It is integrated in the EXTENSION COM board. It ensures the functions below:

 (3)
 Power supply unit (Ref. Fig. 005) The power supply unit delivers these voltages for the command channel: - +5 V BATT from a battery which keeps the FM common memory supplied - +15 V, -15 V, +5 V, +28 V from the filtered aircraft 28 V (Ref.

 1_ ILCPU board
 This board which includes the INNER LOOP processor is equipped
 with a memory module.
 It ensures the following functions:
 - ARINC acquisition of the peripherals for the INNER LOOP
 processor and transmission to the GUIDANCE processor.
 - transmission of data to the peripherals by means of two
 ARINC buses : bus A (high speed) and bus B (low speed).
 These buses are looped back on the GUIDANCE MONITOR for
 monitoring purposes.
 - computation of the AP, FD and A/THR inner loops control laws
 and vote of the AP signals between the command and
 monitoring channels
 - monitoring through comparison of the AP signals between the
 two channels.
 2_ The GUIDANCE part is integrated in the other two boards in the
 command channel.
 The CPU AFS board includes a memory module.
 The GUIDANCE part ensures the functions below: 

 1_ AP engage logic
 Engagement of the AP function depends on:
 - the software conditions of the AP function
 - the status of the GUIDANCE logic (monitoring of peripherals,
 FMGC hardware, watchdog)
 - the status of the long power failure from the power supply
 unit
 - the activation of the AP pushbutton switch on the FCU.
 2_ A/THR engage logic
 The operation is similar to that of the AP engage logic.
 3_ FD engage logic
 Engagement of the FD function depends on:
 - the software conditions of the AP function
 - the status of the GUIDANCE logic
 - the activation of the FD pushbutton switch.
 4_ FCU monitoring
 This monitoring consists in reading, on the FCU bus, the data
 transmitted by the FMGC through the bus A. If an unhealthy
 operation is detected, the FCU FAIL signal is set to FAIL and
 causes the internal reconfiguration of the FCU between FCU 1
 and FCU 2. 

 22-84-00).
 These voltages are monitored by the program which takes into
 account their status.
 A circuit monitors the level of the 28 V and detects any power
 cutoff.

 Three cases may arise:
 -Cutoffs less than 2 ms : these cutoffs have no impact on the operation of the FMGC.
 -Short cutoffs : between 2 ms and 200 ms for the GUIDANCE part and between 2 ms and 4 s for the MANAGEMENT part. The detection circuits provide the safeguard of the RAM memories and enable the microprocessors to restart at power restoration. This transient must not cause disconnection of the AP, FD or A/THR systems
　
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