ARINC 629

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ARINC 629 is an avionic, bi-directional multitransmitter bus system that was specially developed by Boeing for the Boeing 777 (coll. Triple 7). It allows the connection of up to 120 terminals with a data rate of 2 Mbps . The company ARINC (Aeronautical Radio Inc., based in Annapolis, Maryland) specified and standardized the bus system by Boeing under the name ARINC 629th

The bus system, which was developed for use in the avionics of large aircraft to control the systems, is a further development of the ARINC 429 bus system, which has found widespread use in the aviation industry. ARINC 629 is a specification that defines how terminals and connected systems of a bus system can send and receive data. The data is transmitted via a two-wire electrical or optical cable. Every connected system is programmed in such a way that it can send its data at precisely defined time intervals.

There are 2 protocols available for this:

Basic protocol (Engl. Basic protocol )

3 time intervals are defined for this type of protocol:

  • The transmission interval (TI) is the same for all terminals of a bus. It starts when a transfer starts on the data bus. A device may transmit again at the earliest after the TI has expired.
  • The synchronization ( sync gap , SG) is the same length for all terminals of a bus. It is shorter than the TI and starts when there is no transmission on the bus. If another device starts to send before the SG has expired, this timer is reset.
  • The device identifier ( terminal gap , TG) is different for each terminal. It characterizes, so to speak, the order in which the different devices are sent. It begins when the SG has expired and no device is sending on the bus. If another device starts to send before the TG has expired, this timer is reset.

Combined (eng. Protocol combined protocol )

This type of protocol allows preferential handling of non-periodic events. There are three levels of data transfer:

  • Level 1 for periodic data, which, as in the Basic Protocol, are sent in a certain order and without preference. The cycle times are also determined.
  • Level 2 for shorter and more frequent non-periodic events. These data are exchanged at the end of a deterministic cycle.
  • Level 3 for longer and less frequent non-periodic events. These data are exchanged at the end of level 2 as long as there is still cycle time available for this data exchange.

Level 2 and level 3 events are limited in length to one word string. The two types of protocol cannot be used together in one bus.

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