ARINC History and Overview

Aeronautical Radio Incorporated (ARINC)

• Founded in 1929 by four major airlines to provide a single licensee and coordinator of radio communications outside the government
• Only airlines and aviation-related companies can be shareholders, but all airlines and aircraft can use ARINC's services
• Develops and operates systems and services to ensure the efficiency, operation, and performance of the aviation and travel industries

ARINC 429

• A specification that defines how avionics equipment and systems should communicate with each other
• Uses a unidirectional data bus with two signal wires
• Messages are transmitted at a bit rate of either 12.5 or 100 kb per second
• Transmission and reception are on separate ports
• Has been installed on most commercial transport aircraft, including Airbus, Bell helicopters, Boeing, and McDonnell Douglas

Characteristics of ARINC 429

• Data bus uses two signal wires
• Word size of 32 bits
• Bit encoding with bipolar return to zero
• Simplex data bus, with one transmitter but multiple receivers (up to 20)
• No bi-directional data flow on a pair of wires is permitted

ARINC 429 Specifications

• Details the codes used as identifying labels for instructions and the standard types of data used in an aircraft multiplexing system
• Specifies the information protocol, including standard data codes and formats
• Each aircraft may be equipped with different electronic equipment and systems, identified by digital identification numbers called Equipment Identification (ID)

ARINC 429 Data Transfer

• Uses Return to Zero (RTZ) coding
• Signals are transferred by different methods, providing evidence of the flexible nature of digital communications
• Data is transmitted in 32-bit words, with odd parity
• Typically, messages are sent repetitively, with the label field of the word defining the type of data contained in the rest of the word

ARINC 429 Words

• The label is the first 8 bits of a word and identifies the data type and parameters associated with it
• SDI (Source/Destination Identifier) is used to identify the receiver for which the data are destined
• Data field contains the data, which may be in a number of different formats
• SSM (Sign/Status Matrix) contains hardware equipment condition, operational mode, or validity of data content
• Parity bit functions to ensure odd parity in each data word

ARINC 629

• A new industry data bus standard, based on the Digital Autonomous Terminal Access Communication (DATAC) technology
• Adopted in September 1989
• A bidirectional, distributed control bus capable of supporting up to 120 users at a transmission rate of 2 Mbps
• Includes multiple transmitters with broadcast-type, autonomous terminal access

ARINC 629 Interconnection

• Terminals listen to the bus and wait for a quiet period before transmitting
• Users communicate with the bus using a coupler and terminal
• Only one terminal is allowed to transmit at a time
• Protocol timers are used to ensure that each terminal has a chance to transmit

ARINC 629 Interfaces

• Includes the data bus cable, current-mode couplers, and stub cables
• Also includes the Serial Interface Module (SIM) and terminal controller in each Line Replacement Unit (LRU)### ARINC 629 Data Bus
• The ARINC 629 data bus is a high-speed data network used in aircraft systems.
• It is a multi-transmitter system that allows multiple devices to communicate with each other.
• The data bus is made up of a pair of twisted wires with a termination resistor at each end, each with a value of about 130 Ω.

Stub Cables

• Stub cables are used for bidirectional data movement between the Line Replaceable Unit (LRU) and the current-mode coupler.
• They also supply power from the LRUs to the current-mode couplers.
• A stub cable has four wires: two to transmit and the other two to receive.

LRU and Terminal Controller

• An ARINC 629 LRU contains a System Interface Module (SIM) and a terminal controller.
• The terminal controller moves data between the LRU and the data bus.
• Each LRU has a personality that identifies its purpose and operation.
• The personality data are in two parts: Transmit personality PROM (XPP) and Receive personality PROM (RPP).

ARINC 629 Message Structure

• Data in the ARINC 629 system move through the data bus cable and other components as messages.
• Between each message is a Terminal Gap (TG).
• A message is a group of word strings, each with a label word followed by data words.
• Each message has a special structure that allows the LRUs to select and read the message.

Label Word Structure

• A label word is a 20-bit word that contains:
  • A 12-bit label field
  • A 4-bit label extension field
  • A single parity bit
  • A 3-bit time hi lo sync pulse
• A Pre-Sync Sync Pulse (PSSP) and a Pre-Pre-Sync Sync Pulse (PPSSP) occur before the first label word of a message.

Data Word Structure

• A data word is also a 20-bit word that contains:
  • A 16-bit data field
  • A single parity bit
  • A 3-bit time lo hi sync pulse

ARINC 629 Timing

• ARINC 629 uses three timers to prevent accidental signal mixture:
  • Transmit Interval (TI) timer
  • Synchronisation Gap (SG) timer
  • Terminal Gap (TG) timer
• Each LRU uses all three timers to isolate data messages.

Timing Modes

• The three ARINC 629 timers operate in two modes:
  • Periodic mode
  • Aperiodic mode
• Periodic mode ensures that an LRU transmits at a regular time sequence, in the power-up order.
• Aperiodic mode is used when an LRU message length increases due to a non-normal condition.

Periodic Mode

• In periodic mode, an LRU transmits once every TI.
• The timing diagram shows the sequence of events for three LRUs in the periodic mode.

Aperiodic Mode

• Aperiodic mode is used when the sum of all TGs, transmission times, and SGs is greater than the TI.
• Aperiodic data are a direct result of a discrete event and are asynchronous and updated at a non-uniform rate.
• Aperiodic data transfers data about events important to aircraft operation, such as position reports in landing gear systems.