scope:

Data bus technology provides an efficient means for the transfer of data between a number of processors, controls, displays, sensors, etc. within modern aircraft avionic systems. The first data bus standards to find general acceptance in the aerospace industry were Def Stan 00-18 (Part 2)/US MIL-STD-1553B for military aircraft and ARINC 429 for civil aircraft. The continued development of avionic systems has demanded data bus technology with ever higher performance, particularly speed, which has led to the development of avionic bus systems with signalling speeds in excess of 100 MHz.

With the recent developments in modular avionic systems, it has become apparent that there is also a need for the application of data bus technology to low level utility functions such as simple proximity detectors, oxdoff discretes, indicators, relay and electrical load controls, etc. which still exist in modular systems. These demand high integrity operation in the harsh avionic environment but must be provided at a lower cost to connect.

The bus system defmed in this standard is designed to meet the above requirement by providing a high integrity, low cost solution based on the proven technology of Def Stan 00-18 (Part 2)/MIL-STD-l553B. It retains centralised control, commandresponse philosophy and use of transformer isolated terminals coupled to a shielded, twisted pair, medium but operates at 250 kbit/s with an addressing limit of 126 terminals. In practice the actual number of terminals and maximum bus length is constrained by the electrical parameters of the implementation.

Even with the use of this standard, subtle differences may still exist between Utilities data buses used in different applications due to the options allowed in the Standard; systems designers must recognise this fact. These designer selected options must exist to allow the necessary flexibility to assemble a custom Utilities data bus system from the functionally standard parts. Alternative coupling methods are defined in supplements to this Standard.