wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

Embedded Networks in Civilian Aircraft Avionics Systems 24-3
ARINC standards: ARINC 651 for the description of the modular hardware architecture [ARI91] and
ARINC 653 for the modular software architecture [ARI97]. More recently, the ARINC 664 has provided
an answer to the problem of increased communication by multiplexing huge amounts of communication
data over a full-duplex switched Ethernet network [ARI02,ARI03]. It has become the reference
communication technology in the context of civilian aircraft avionics since it provides a backbone
network for the avionics platform.
24.3 Classic Avionics and ARINC 429
ARINC 429 is the earliest and most commonly used standard for civilian aircraft avionics and has
been installed on the majority of Airbus and Boeing aircraft. It employs a unidirectional data bus
standard known as the Mark 33 digital information transfer system (DITS). Messages are transmitted
over two twisted pairs by the owner of the bus to other system units at a bit rate of either 12.5
or 100.kbps. The specification defines electrical transmission characteristics and protocol data unit
features [ARI01].
The ARINC 429 protocol implements a mono-emitter broadcast bus with up to 20 receivers. Messages
sent by the sole transmitter consist of a single 32 bits data word. The label field of the word defines the
type of data that is contained in the rest of the word. ARINC 429 data words use five primary fields:
parity, SSM, data, SDI, and label. As represented in Figure 24.1, the ARINC 429 data word is composed
as follows: bit 32 is the parity bit; bits 31 and 30 contain the sign/status matrix (SSM) field that contains
equipment conditions, operational modes, or validity of data content; bits 29 through 11 contain the
data; bits 10 and 9 provide a source/destination identifier (SDI); and bits 8 through 1 contain a label
identifying the data and associated parameters.
The label is an important part of the message. It is used to identify the transmitted data and to determine
the data type. The emitter broadcasts the data (with a given periodicity) on the bus and does not
know which equipment will receive a given instance of data. Each receiver filters the data according to
the label of each data. The SDI is used to identify the receiver to which the data is destined. If a given
label can be sent on different data buses, it can also be used to identify the source of the transmission (as
units are assigned digital identification numbers called equipment id).
ARINC 429 is confronted with an increasing number of intercommunicating avionics functions. The
(point to multi-point and unidirectional) characteristics of the ARINC 429 protocol mean that the avionics
system must include an ARINC 429 bus for each communication path as depicted in Figure 24.2.
32 31 30
29 11 10 9 8 1
P
SSM
Data SDI Label
FIGURE 24.1
ARINC 429 data word.
F1
F2
F3
G1
G2
FIGURE 24.2
Classic avionics architecture.
© 2011 by Taylor and Francis Group, LLC