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COMMUNICATIONS PROTOCOLS IN AERONAUTICS

by George Novacek

Start ý Data Bus Systems ý Timing is the Secret ý ARINC 429 ý CSDB and ASCB ý MIL-STD-1553B ý ARINC 629 and Beyond ý ARINC 429 Implementation ý Data Format ý Wrap Up ý Sources and PDF

MIL-STD-1553B

MIL-STD-1553B is a bidirectional, centrally controlled data bus predominant in military aircraft. It was originally developed in the early ý70s and since then has continuously improved. Its official name, Digital Time Division Command/Response Multiplex Data Bus, immediately betrays its military origins. Because the bus has been used extensively in critical systems for such a long time, its characteristics and performance under various adverse conditions are well-known. Thus, there is no hesitation to use it for data communications in fly-by-wire aircraft, in which data corruption would be more than likely catastrophic. (The fly-by-wire description is used when flight surface movement affecting pitch, roll, and yaw, traditionally performed by mechanical links, is done by servo systems. All highly maneuverable, thus unstable military aircraft today and many new commercial aircraft fall into this category.)

The 1553 bus sets one terminal as a BC and can support up to 31 users, called remote terminals (RT), with a bit rate of 1 Mbps. And because it would be silly to risk losing a multimillion-dollar airplane because of a stray bullet cutting a wire, this data bus is fully dual-redundant. It also exists in fiber optic implementation, which is defined in specification MIL-STD-1773. [1] Fiber optic interface has been used in applications in which exposure to HIRF (high-intensity radiated field), lightning, and otherwise unpleasant electromagnetic interference can affect data integrity.

Although the MIL-STD-1553B data bus doesnýt achieve the performance and flexibility of many modern commercial data buses, where lives or huge investments depend on transmitted data integrity and reliability, it unquestionably reigns supreme. Why isnýt it more commonly used? The main reason is cost. A chipset with the interface transformers for one RT costs well over $1000, a price tag hard to justify on systems in which the 1553Býs excellent performance isnýt needed.

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