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MIL-1553- What does it mean?

MIL-1553 was originally issued by the Department of Defense for military applications. It defines standards for functional, mechanical and electrical characteristics of the serial data bus commonly used in the avionics of military aircraft. It was developed when the integration of computers systems into military aircraft became imminent. Prior to employment of the data bus for digital communications, transmissions were carried through cables. Erwin Gangl one of the earliest scientists to work on this project set up a method to facilitate digital communications among all avionics systems, such as radar navigation and data displays by employing the serial data bus, rather than miles of cable.

First seen in the 70's on military fighter jets, it is has both military and civil applications. The standard covers the data bus and all associated interface electronics. 1533 governs bus and terminal operation, data flow, error handling, hardware and wiring. Although new technology would seem to threaten its longevity, durability of 1533 can be attributed to its vast international installed base. With so many installations, manufacture of compliant systems is still good business. So what is the scope of MIL-1533 and what does it mean in avionics?

Testing
To be 1533 compliant, all components must to work properly under all environmental conditions to which it will be subjected. Consider its application for devices used on spacecraft which will be subjected to temperature and electrical field extremes. MIL-1533 does not specify the environmental conditions for testing. These will be determined by the intended use of the specific device employing the multiplex data bus.

Operations and Messaging
1533 defines data flow, error handling and terminal operations requirements. A uniform approach to message transmission, data and error handling bus components and the associated interfaces, assures interoperability. Specifically, multiplex data bus systems must function asynchronously in command/response mode, with transmission occurring in half-duplex. Information transmission control resides solely with the bus controller. Messages are formed by specified command, data, and status words. The standard provides a high degree of interoperability. Standard interchangeability makes maintenance manageable and allows for a fair amount of innovation in employing various 1533-compliant components.

Hardware
Beyond the two-conductor, twisted, shielded, jacketed cable requirement, the standard defines impedance, attenuation, termination and stub requirements. This section also governs the noise emitted by operations as well the tolerance of data transmissions for noise in the environment. Given the challenging environments in which avionics components operate, strict standards must be employed with the physical construction of the data bus and associated electronics.

Redundancy
All standards for testing operations and hardware apply in their entirety to all redundant systems. There are additional requirements to isolate the redundant components to avoid a failure of one eliminating the other as a viable back-up and support a high degree of fault tolerance. In general, the standard provides for only one data bus being active at a time. The redundancy standards in MIL-1533 are flexible enough to accommodate a variety of applications while still maintaining integrity in redundancy.

Article Source: http://articledashboard.net

Excalibur Systems is the leader in providing the Aerospace Industry with high quality, cost effective data bus interfaces, data recorders, 1553 coupler, cables, connectors and Integrated Solutions. Excalibur Systems' line of products provides support for MIL-STD-1553, ARINC-429 and other military and commercial avionics specifications.

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