Overview of MIL STD 1553
MIL STD 1553 is a hardware and software standard for interconnecting electronic equipment. It is used for many US military aircraft and some military vehicles such as the Bradley Fighting Vehicle and the Abrams M1A2 Battle Tank. It is also found in some foreign aircraft such as the British, Italian, German and Saudi Panavia Tornado and Eurofighter Typhoon. The Russian MiG-35 and the International Space Station use it as well. The French, of course, have something like it, but constructed differently.
The first version was published in 1973, the second version (1553B) in 1978. Change notices have tightened up the specification for ease of interoperability. There is a similar civilian systems called ARNIC 429 which is not inter-operable but has the same basic purpose.
A MIL-STD-1553 B system consists of several elements:
- at least two redundant buses made up of
- cabling — twin-ax (shielded cable like coax with two internal conductors)
- bus couplers — device containing bus in and out, and one or more transformer isolated stub connectors which are used to connect to the bus controller, backup bus controller(s), bus monitor(s) and remote terminal(s)
- terminators — resistors with the characteristic impedance of bus, connected at each end of the bus
- connectors — military-specific ruggedized connector
- exactly one bus controller — contains the instructions for controlling communications over the bus and provides commands to control the operation of the remote terminals
- one or more backup bus controllers — takes over as bus controller if the current bus controller fails
- zero or more bus monitors — records bus traffic but does not produce any
- some remote terminals — interface with other equipment or provide a connection to another 1553B system
The system operates at a one megabit/second rate, using Manchester encoding which is self-clocking. The transmission unit is a 16-bit word. The words contain commands, status or data. Data can be time-division multiplexed at various rates. The rates typically are 50 Hz and its sub multiples of 25, 12.5 ... Hz. Remote terminals can not initiate data transfers but they can request them by setting request bit(s) in their status words returned in response to polling from the bus controller. It is the responsibility of the bus controller to poll often enough.