(2)
CDU controller and keyboard/annunciator interface circuits contain a microprocessor and programmed memory. These circuits perform keyboard decoding and data display on CRT. They also control the FMC FAIL, MSG, and EXEC annunciators.
(3)
Video and deflection circuits provide horizontal and vertical position deflection of the characters on the CRT screen.
(4)
Automatic brightness control circuits provide display brightness control, in conjunction with the manual BRT knob and the automatic sensors. These circuits also provide power-on reset, annunicator regulator, and BITE, and CRT protection monitor.
(5)
A low voltage power supply, within the CDU, provides the necessary operating voltages for the circuit card assemblies.
(6)
A high voltage power supply, within the CDU, provides the high voltage necessary for operating the CRT.
L. The Airplane's master dim and test circuitry provide 28v dc to CDU for annunciator lighting and lamp test.
5. Flight Management Computer__________________________
A. General
(1) The FMC provides optimal speed, thrust, and flight path guidance. This optimization is based upon real time sensor measurements of actual flight conditions, and the operator's definition of flight cost factors to be optimized. The optimal performance calculations that determine climb, cruise, and descent schedules are embedded in the FMCS program, and they automatically provide the required speed and thrust limit targets which can be coupled by vertical guidance commands to the airplane's autopilot and autothrottle systems. The primary cost economical mode (ECON) is selected automatically by the system without operator input. Other modes may be manually selected if operating conditions warrant.
B. FMCS Digital Inputs (Fig. 3)
(1)
The FMC receives data in digital format from several different sources. The Digital Analog Adapters (DAA), collect data from various analog sensors, and reformat the analog data into digital ARINC 429 format. The DAA digital outputs are applied to FMC input ports.
(2)
Figure 6 shows all of the input data words read by the FMC.
C. FMC Digital Outputs (Fig. 6)
(1) The FMCS provides digital data to various systems. Four output buses are used. Figure 6 shows the FMC output data words, and the systems that use the words.
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A 737-300/400/500MAINTENANCE MANUAL
115V AC
ELLEX
C1018
PWR GND
PWR 1
CDU 1 CHASSIS GNDP18-2 CIRCUIT BREAKER PANEL
BRIGHT/DIM
5V LIGHTING
CDU LOCATION
ANNUNCIATOR LIGHTS
DATA FROM FMC
DATA TO FMC
FMCS Control Display Unit Simplified Schematic
Figure 8
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737-300/400/500MAINTENANCE MANUAL
D. Discrete Input/Output
(1) In addition to the digital inputs and outputs, discrete signals are also input to and output from the FMC. The discretes are either 5-volts or 28-volts. These signals are buffered and translated to TTL logic levels within the FMC. Management and interpretation of these discretes is a function of the I/O processor.
E. FMC Modules (Fig. 9)
(1)
There are 4 modules, or cards in the FMC. These modules are the processor, memory, ARINC I/O, and power supply cards. The cards are interconnected through a terminal board, which has a fiberglass core with pressed in connector pins. All of the cards , except the power supply card, are keyed so they cannot be plugged into the wrong slot.
(2)
Processor Card
(a)
The processor card does most of the functions associated with navigation computations. These functions include management of the CDU, and lateral and vertical steering guidance. It also does most of the functions associated with the performance computations. These fuctions include vertical steering guidance (relating to target speeds) and flight envelope protection.
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