REMOTE GROUND 
TEST SWITCH 
E2 
SEE  E  LEFT CENTRAL 
E1  MAINTENANCE 
COMPUTER 
SEE  D 
REMOTE CONTROL 
DISPLAY UNIT 
FWD  RIGHT CENTRAL 
SEE  F  MAINTENANCE 
COMPUTER 
SEE  D 
MAIN EQUIPMENT CENTER 

LEFT OR RIGHT CENTRAL MAINTENANCE COMPUTER
D
GND TESTS
ENABLE
NORM
REMOTE GROUND TEST SWITCH REMOTE CONTROL DISPLAY UNIT EF
Central Maintenance Computer System - Component Location Figure 1 (Sheet 2)
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 2.  Central Maintenance Computer (Fig. 1)
____________________________
 A.  Two identical central maintenance computers (CMCs) are installed in the main equipment center. Both CMCs are powered in normal operation and both simultaneously process fault messages. All system inputs to the CMCs are connected in parallel to both CMCs. Discrete outputs from both CMCs are spliced together in airplane wiring. Digital output buses are switched by relays within the CMC installed in the left position so that only one CMC transmits digital output information at any given time. In normal operation, digital output information is provided by the left CMC. If the left CMC fails, automatic switching occurs so that the right CMC provides the outputs. The CMCS can be fully operational with only one CMC installed. However, this single CMC must be installed in the left CMC position.
 3.  Ground Test Switches and Relays (Fig. 1,5)
_______________________________
 A.  The ground test switches, together with the enable relays permit or prohibit the transmission of test initiation signals from the CMC to the LRUs.
 B.  Ground Test Switches
 (1)  
One ground test switch is installed in the flight compartment. A remote ground test switch is installed in the main equipment center.

 (2)  
When both switches are in the NORM position, initiation of some ground tests by the CMC is inhibited. This inhibit is in addition to the inhibit features of the specific LRUs. When at least one switch is in the ENABLE position, ground test initiation is permitted.

 C.  Enable Relays
 (1)  
Eight relays are installed in the main equipment center.

 (2)  
The relays are controlled by the ground test switches. When both switches are in the NORM position, the eight relays are open and test initiation signals from the CMCs cannot get through to the LRUs. When at least one switch is in the ENABLE position, the relays are closed and CMC test initiation signals can get through to the LRUs.

 4.  Printer (Fig. 1)
_______
 A.  The multiple-input or full-format printer is used to generate reports of fault data shown on the CDU. The printer is installed in the flight compartment. A <REPORT prompt on the CDU is provided when a printer report can be made of the display.
 5.  Control Display Unit (Fig. 1)
____________________
 A.  The control display unit (CDU) is the primary crew interface for the CMCS. The CDU is also the primary crew interface for several other systems and is actually part of the Flight Management Computer System (AMM 34-61-00/001). The CMCS uses the CDU to display maintenance information. When the CMCS is the active system on the CDU, everything on the display is generated entirely by the CMCS.
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IDS AIRPLANE INTERFACE  CMC DIRECT 
AND  INPUT AND 
CMC INDIRECT INTERFACE  OUTPUT 

CMC - IDS Interface
Figure 2

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