The MIL-STD-1553 Specification

11 August, 2016

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MIL-STD-1553 is a specification established by the Air Force and the USDD (United States Department of Defense) in 1973 that outlines the physical, electrical, and operational properties of serial data buses. It was first intended to be a data bus used for Air Force avionics, but today is frequently applied to OBDH (on-board data handling) systems in military and civilian spacecrafts. Its use has spread to all U.S. military sectors, in addition to NATO where it's designated as STANAG 3838 AVS. It includes several repetitive physical layers, a control panel for differential networks, time sector multiplexing, command and response protocols, and is capable of managing as many as 30 long-distance terminals. 

The Primary Characteristics of MIL-STD-1553

A few of MIL-STD-1553's primary elements include the control bus, the built-in long-distance terminal (an antenna or other type of sensor system that has a unique internal 1553 configuration), the independent long-distance terminal, the bus monitor, the twisted pair data bus cables, and optional isolation couplers.

The Control Bus

The primary task performed by the system control bus is providing data flow control for all of the bus feeds. This function makes the control bus the only way of establishing communication, which it can do using either a command or response approach.

The Long-Distance Terminal

The built-in long-distance terminal is comprised of a number of circuits found within an antenna or other radar device that's attached directly to the data bus. The main function of the terminal is to execute data transference to and from the sensor with the guidance of the control bus. These kinds of terminals don't always have control bus functionality, but if the subsystems are reasonably smart on their own, they may be able to function as secondary control buses.

The Bus Monitor

The MIL-STD-1553 bus monitor records any messages and aggregates all data contained by the data bus. The most important uses for this type of function include gathering and storing digital information locally for long-distance telemetry, and being used as an offline auxiliary controller to monitor the condition and functionality of the main system and all of its related subsystems.

The Data Bus

Next up is the system data bus itself. The specification lays out certain guidelines for the twisted pair wire cables the data bus uses, in addition to specific classifications for hook-up polarity.

The Data Bus Coupler

The data bus in-line coupler device separates the primary bus from its terminals. MIL-STD-1553 currently supports two kinds of data bus connection strategies: Transformer coupling and direct coupling. Both of these types of data bus couplers help to protect the primary data bus against short-outs on individual stubs. The range of resistor values, the transformer’s voltage ratio, and the receiving unit's electrical impedance are laid out so that stubs seem like clean or high-impedance ports to the primary bus. This system minimizes the amount of interference on the primary data bus caused by signal terminations.

 

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