TE - White Papers

8 AEROSPACE / WHITE PAPER CONNECTING THE FUTURE OF FLIGHT CANbus SERIAL COMMUNICATIONS for real-time control with low data rates VALUE For transmitting altitude, velocity, position, motor parameters, and other flight-critical data, commercial aircraft use the Controller Area Network (CAN) bus serial interface to connect LRUs (line replaceable units) with inertial measurement units (IMUs). CANbus microcontrollers and devices—such as a temperature sensor—can communicate with electronic control units (ECUs)—such as an engine ECU—without a host computer. The deterministic CANbus protocol handles fly-by-wire electronic control for flaps, trim, engine controls, and autopilot systems in place of direct mechanical linkage between the flight controls and flight surfaces. And in glass cockpits, CANbus connects radio system control panels on the flight deck to radio system LRUs, engine control interfaces, and LCD flight instrument displays. Used in point-to-point wiring, shielded-twisted- pair CANbus cable is compact, saving space and minimizing weight in an eVTOL airframe. PERFORMANCE Originally developed in the 1980's by Bosch GmbH for automotive control systems, CANbus was subsequently adopted for aircraft—notably the Airbus A380—with physical interfaces, data formats and other features suited for avionics systems. CANbus provides distributed real- time control by broadcasting transmissions to all nodes. There is no explicit address in the message frame. Intelligence in a CAN node's software or acceptance filtering applied by a CAN hardware controller processes the transmitted message's ID to receive relevant return messages. Bandwidth and Data Rates The classic CAN frame format handles short messages with up to an 8-byte data payload. Available in different versions, the maximum bit-rate of "high speed" CANbus (ISO 11898) is 1 Mbit/s. The CAN arbitration method limits the length of the network link. At 1 Mbps, a theoretical length of 40 meters can be maintained. But practically, cabling, connectors, and other physical-layer components necessitate shorter lengths. Slower bit rates allow longer cables. A recently introduced format, the CAN Flexible Data (CAN FD) protocol accommodates 64- byte payloads and faster bit rates for up to 600 percent higher throughput. ARINC 825 Supplement 4 defines enhanced capabilities for CAN FD technology, which accommodates 4 Mbps data rates and increases payload size from 8 byte to 64 bytes. For CANbus implementations, TE can provide the full physical-layer solution, including cables, connectors, and terminations, as well as the ability to manufacture finished point-to-point harnessing. Raychem SAE J1939-compliant CANbus cables support speeds up to 1 Mbps. Shielded and unshielded variations are available in wire weights from 18 to 26 AWG allowing flexible construction for easier routing through the confined spaces in UAM airframes. TE TECHNOLOGIES FOR CANbus EXPLORE THE PAPER: CHALLENGES ARCHITECTURE SENSORS IMPLEMENTATION OPPORTUNITIES NETWORK

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