MIL-STD-1553

MIL -STD -1553 ( MIL, for short - bus) is the name for a field bus, which the U.S. Air Force introduced in 1973.

Properties

Data is serially transferred at a rate of up to 1 Mbit / s. Transferred words consist of 20 bits: 16 bits for the information, three preceding bits for synchronization and a trailing control bit for the ( odd) parity. They are transmitted in half-duplex operation, and either belong to the category of data, command or status.

The abbreviation stands for military and MIL STD for standard. The MIL -Bus is widely used in military aircraft and in space to control the system components, while has established itself in the automotive industry, the CAN bus. Thus the MIL bus in the Ariane 5, the ISS is to find and was in the Space Shuttle in use. However, consists in space for high data rates of SpaceWire through. The civil aviation, however, is ARINC busses, mainly the ARINC 429 bus, which can be found today in most commercial aircraft models.

Structure

MIL-STD -1553 - structure consists of a bus controller (BC), and up to 31 remote terminals (RT).

Bus module:

• The bus controller organizes the flow of data on the fieldbus. The BC is a stand-alone computer in the airplane in the system dar.
• Each remote terminal provides an interface for a device on the plane dar. This interface allows the unit to participate in the bus.
• The bus monitor is a test device at which the bus is monitored. This test facility can record all data on the bus or play directly at run time, making errors in transmission can be detected.

Communication process

There are basically three different directions of communication. BC to RT, RT to BC and RT to RT. In addition, a broadcast functionality is supported, in which a bus station (BC or RT) sends to all other connected RTs. Any communication via the bus - both BC to RT, RT to BC and RT to RT - is initiated by the bus controller.

In concrete terms, a communication looks like in the following image.

Electrical Design

To enhance the noise immunity, the system components are electrically isolated from the mains. In the simplest case, an inductive transformer couples a signal. This is possible because the signal level due to the Manchester encoding are DC-free. There are various possibilities for coupling: Transformer Coupled or Direct Coupled. Transformer coupled means that the bus is terminated by a resistor network to the transformer. "Direct" means that the RT or BC is terminated with resistors to its transformer side, there are no resistors in the bus, so also direct.

In this case, there is a primary and a secondary channel (which are redundant, that is, it can never be simultaneously transmitted on the primary and secondary channel). Each channel has two signal lines on which the data is transmitted: one signal ("true" ) and signal two, as its complement. The signals are differentially measured, resulting in a lower susceptibility to interference according to. It is a Balanced signal transmission, or more precisely a " Differential transmission. "