Chapter 2. Digital Data Bases

2.4. Standard ARINC 629 for DDB

ARINC 629 represents the standard for DDB organization, and is oriented to ensure communication of type 'single source - many receivers' within "mane transceivers - many receivers". It is developed for usage while civil aircraft construction and implementation. It was used in 1989 for the first time, when Boeing 777 was being structured.

ARINC 629 is a rapid DDB in comparison to ARINC 429, which provided 100 Kbit/sec the elective-transmission speed. The transfer rate of ARINC 629 is 2 Mbit/sec, what is 20 times faster than ARINC 429, and 2 times greater than MILSTD-1553B.

The principle of operation is the same as of MILSTD-1553B. Separate modules join the overall transmission data bus. In general, ARINC 629 support the connection to 128 certain LRU to one data bus [44; 71]. Moreover, data buses are twofold or threefold reserved to ensure the reliability for essential PC systems (fig. 32).

Fig. 32. ARINC 629 Structure

One data bus allows the connection of up to 128 LRU, however each of them can have an own subnetwork, which includes, for example, certain PC subsystem (fig. 33).

Fig. 33. The links construction in ARINC 629

Unlike MIL-STD 1553B, ARINK 629 doesn't have a bus controller as a separate block. The controller function is done by special connection block (looking like a microcircuit), which is integrated into each LRU. The access to a data bus transmission is provided according to time conception. At that, some time interval is devoted to each LRU in a network, during which there is a possibility to transmit information to the data bus. The information in data bus is received only with a certain LRU, to which it was addresses, correspondingly to the indicated address.

A digital message of ARINC 629 (fig. 34) consists of digital lines, total amount of which can be changed up to 31. Each digital line consist of the name and certain amount of digital words (up to 256 digital words in one digital line).

Each digital row consists of the name and certain number of digital words (up to 256 digital words in one digital row).

Fig. 34. Message structure of ARINC 629

The structure of digital word can be different depending from transmitted information.

The information by ARINC 629 can be transmitted either primary or combined protocol. The simple example of transmitting of information by ARINC 629 in the network of three LRU (LRU1, LRU2, LRU3) by the major protocol is shown on fig.35.

Each LRU has the same interval of transmitting information, which is defined by system configuration (0.5-64 ms), which begins always when LRU transmits messages (M). The message contains the unique name of module (NM), which is different for each LRU. The name of the module is transmitted each time before the beginning of new interval of transmission or after synchronization. Se synchronization signal (S) is the same for all LRU and is given after finishing the transmission of the message by the last LRU.

Within each cycle of information transmission the sequence of delivering of information to the data bus is set in advance. The general order of all LRU is recorded in the internal memory of each of the control units of LRU. After transmission of the message (M) by first LRU, next LRU in turn gives its NM by which its message M is transmitted and so on.

Fig.35. Transmission of messages by ARINC 629

The increased speed of data transfer and more technological flexibility of ARINC 629 gives him more advantages compared to ARINC 429 in building onboard DDB civil for PC of civil aviation.

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Avionics training in details by
Ostroumov IvanOSTROUMOV Ivan, PhD
Associate Professor, www.ostroumov.sciary.com