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AS5643 - The Leading Fly-by-wire Technology

AS5643 has become the leading fly-by-wire bus interconnect solution. Fueled by the success story of integration in the F35 program, AS5643 provides many advantages over other solutions and represents the most technologically innovative yet cost effective solution available in the market right now.

A summary view

  • AS5643 and 1394b deliver a flexible and deterministic solution for state-of-the-art aerospace and defense applications.
  • AS5643 provides the data latency, data coherency and efficiency along with the redundancy and robustness required for future manned and unmanned aircraft.
  • AS5643 together with IEEE-1394b provide the interface requirements for Military and Aerospace Vehicle applications.
  • 1394b is a high speed serial bus capable of 122Mbit/s (S100) to 3.92Gbit/s data rates on a network consisting of daisy-chained, starred, treed and looped topologies and supports copper and fiber optic wiring.
  • Asynchronous stream packets are used to send Anonymous Subscriber Messages.
  • Pre-assigned addressing and bandwidth ensure deterministic operation and high reliability.
Click on image to enlarge


Determinism via mapped transmission timing -
  • Time synchronization is determined by the Control Computer (CC) sending out Start of Frame (STOF) packets at the specified frame rate (typically 80Hz or 100Hz).
  • The ASM messages are transmitted at the network profile assigned offset times relative to the STOF.
  • Receiving nodes can deterministically anticipate and therefore guarantee resources are available and therefore guarantee the message can be received and processed.
  • The network profile system architecture determines the frame rate and offset time for every node on the 1394b bus.
  • Offset times can be adjusted during initialization.

It is important to understand that AS5643 provides a framework for this timed transmission scheduling. The real mapping (assignments of real values for STOF period, relative STOF offsets, ...) is not covered in the AS5643 specification or the so-called slash sheets. This process is deferred to the actual project ICD and the system development efforts of the individual avionics programs. AS5643 provides examples (e.g. the STOF period of 80Hz/12.5ms) but programs are free to develop their own timed mapping.

Fault tolerance

Triple Architecture -

Fault tolerance in a Vehicle System Data bus is essential to keep an aircraft flying even when one or more components fail.

  • AS5643 capitalizes on 1394b loop topology support to create the first level of fault tolerance.
  • Dual- or triple-redundant system architecture provides a second level of fault tolerance.
  • CRC and Vertical Parity Check (VPC) provide both bus level and system level error detection.
  • Remote node (LRU) generated heartbeat is monitored by the Vehicle Management Computer (VMC), to ensure the device is operational and sending fresh data. 

Low Cost, Low risk

  • Unlike other technologies, AS5643 didn’t create new requirements causing changes to existing COTS 1394b silicon solutions.
  • CC’s typically use the same Open Host Controller Interface (OHCI) implementations used in Macs and PCs.
  • LRU’s typically use the same general purpose implementation used in cameras, robotics and other industrial applications.
  • In addition to nearly two decades of commercial use, 1394 and AS5643 are actively being used in multiple aerospace and defense programs, e.g. Fix wing, Rotorcraft, UAV, Missiles and Spacecraft.
  • Takes full advantage of existing 1394 ecosystem such as chipsets, IP-cores, software stacks, test and measurement equipment and manufacturing test systems.

SAE Standards

Within the SAE Aerospace Systems (AS-1A-3 group) the following standards or recommendations have been developed relating to AS5643 and IEEE-1394

  • AS5643– IEEE-1394b Interface Requirements for Military and Aerospace Vehicle Applications
  • AS5643/1 – S400 Copper Media Interface Characteristics Over Extended Distances
  • AS5657 – Test Plan/Procedure for AS5643 - AS5706 – Test Plan/Procedure for AS5643/1
  • AIR5654 – IEEE-1394b for Military and Aerospace Vehicles – Applications Handbook
  • New slash sheets for S100 and S200 over copper

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