(c)
Main Processor (CPU and I/O) Assembly This module contains the CPU that executes the signal processing using a microprocessor. It also contains the I/O section consisting of ARINC 429 transmitters and receivers, and discrete I/O logic to provide the interfaces with other aircraft systems including the Centralized Fault Display System (CFDS) and displays. ARINC 429 inputs and outputs are processed by a specially designed ARINC 429 LSI transceiver device. External level converters are used to satisfy the ARINC 429 characteristics for the transmitters and convert input ARINC 429 signals to logic levels. All discrete inputs and outputs external to the DME are processed by discrete components to provide level shifting and latching. The following types of devices are employed:
-digital-to-analog converter devices to generate control and test signals,
-Field Programmable Logic Array (FPLA) devices to accept, decode and generate discrete signals,
-memory devices (bootstrap, program, nonvolatile, and data),
-data recorder interface,
-front panel display driver,
-RS-232 interface,
-clock generators.
(d)
Video Processor This module contains a Field Programmable Gate Array (FPGA) which is the control center for the video processor. The video processor provides the following operations:
-converts tuning commands from CPU to serial data to tune the transmit/receive frequency synthesizer,
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generates the corresponding receiver preselector tuning
voltage,
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generates the corresponding X or Y pulse modulation for the interrogation,
-
generates the output mutual suppression pulse for an
interrogation,
-detects the input mutual suppression pulse and inhibits
reception and video processing,
-determines the logarithmic IF noise threshold setting,
-starts the range (distance) counter when an interrogation is transmitted,
-digitizes the video signals from the receiver logarithmic IF amplifier,
-validates the amplitude, spacing, and width of the digitized video pulse pairs,
-stores the range counter value in a FIFO when each valid pulse pair is decoded,
-analog-to-digital converter devices to process the received signals and BITE test point voltages,
-generates the audio tone for the Morse code station identity aural output,
-provides for integrity testing.
(e)
Power Supply Assembly This module is a self contained, high efficiency power supply that converts the 115 VAC, 400 Hz AC power into the required DC operating voltages (+70V, +24V, +12V, -12V and +5V). It includes an EMI filter to reduce electromagnetic interference from being radiated from the power lines.
(f)
Rear Interconnect Module The rear connector assembly provides the interwiring from the aircraft interface to the internal modules. A combination of series resistors, series of transient voltage suppressors, and ferrite pin filters provide High Intensity Radiation Fields (HIRF) and lightning protection. To prevent HIRF or lightning from affecting operation by entering via rear connector cables, a HIRF compartment is formed in the rear of the DME Interrogator. The signal and power cables are filtered by using discrete and distributed filter elements and limiting devices on the rear interconnect module located inside HIRF compartment. The filtered lines are then fed to the appropriate points in the DME Interrogator. The DME Interrogator is packaged in an aluminum casting. This seamless main frame ensures HIRF cannot enter the unit through structural seams. The slots formed by the removable side covers are sealed against HIRF with protective gaskets and metal covers.
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(g)
Front Panel Display Module The front panel display module is mounted behind the front panel and provides an interface to an operator via a low-power Liquid Crystal Display (LCD) that is visible from the front of the DME Interrogator. In addition to the LCD, the module contains "Light Pipe" back lightning, temperature compensation circuitry, and a PC board containing an associated LCD driver, two pushbutton switches used to enter functional test and to control the display menus, and a nine-pin, RS-232 serial type connector.
(h)
Memory Card Interface Module The memory card interface module is used to load data into the CPU or record data from the CPU. The memory card interface module supports either flash cards or RAM cards via the front panel Personal Computing Memory Card Interface (PCMCIA) slot. The flash card or RAM card is inserted through the front panel. In one mode, data stored on the flash card memory module is used to update program or data memory in the DME Interrogator. In another mode, the flash card memory module functions as a data recorder.
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