ARINC 429

ARINC 429 is a two-wire data bus. Connecting conductors - twisted pairs. The word size is 32 bits, and most messages consist of a single data word. The specification defines electrical, communication, and protocol specifications. ARINC 429 uses a unidirectional data bus standard (transmission and reception lines are physically separated). Messages are transmitted at one of three speeds: 12.5, 50 or 100 Kbps. The transmitter is always active, it either transmits 32-bit data words or gives an “empty” level. No more than 20 receivers and no more than one transmitter are allowed on the bus.

Each ARINC word is a 32-bit value that contains five bit fields:

• Bit 32 is a parity bit, and is used to verify that the word was not damaged or distorted during transmission. Parity Bit
• Bits 30 to 31 are the "Sign Matrix" or status, or SSM (Sign / Status Matrix), and often indicate whether the data in the word is valid.
  • Working state - The data in this word is believed to be valid data.
  • Test state - data is provided for test purposes.
  • Failure - Failure of the hardware associated with the issuance of this word.
  • None - Data is missing, inaccurate or outdated for some reason other than hardware failure. For example, autopilot commands will show this state when autopilot is not turned on.
    • Sometimes this field may indicate the sign (+/-) of the data or be part of the information. A reverse code is used to transmit a negative value.

• Bits 11 - 29 contain basic data. Bit fields written as a binary decimal code or binary optional code are standard for the ARINC 429 data format. Also, the bit field format can be mixed.
• Bits 9 and 10 - “Source / Destination” identifiers. Indicate which receiver this data is intended for, or, more often, which subsystem transmitted the data.
• Bits 1 - 8 contain a label (label), represented in octal number system . They are the identifier of the data.

Label recommendations are provided in the ARINC 429 specifications for various types of equipment. Each aircraft can contain many different systems, such as a flight control system , an inertial navigation system , an air signal system , a radio altimeter , a radio , and GPS sensors. For each type of equipment, a number of standard parameters are defined, the same for all manufacturers and models. For example, any inertial navigation system represents the barometric altitude of the aircraft as a 203 mark. This allows to some extent the interchangeability of parts, since all inertial navigation systems behave, for the most part, in the same way. However, the number of tags is limited, so tag 203 can have some completely different values ​​if sent by a GPS sensor. However, usually different aircraft systems use tags regardless of source. In addition, as is usually the case with any specification, each manufacturer has slight differences from the formal specification, for example, additional data is added that are not described in the specification, not taking into account some of the data recommended by the specification, etc.

Standards

• http://www.arinc.com/ (registration and payment required)
• http://protect.gost.ru/document.aspx?control=7&id=153197 (GOST)

Study guides

• [1] (inaccessible link) Serial channel of information exchange in accordance with GOST 18977-79 (ARINC-429)
• ARINC Tutorials by Ballard Technology, Inc.
• ARINC-429 Tutorial (video) from Excalibur Systems Inc.
• ARINC Protocol Tutorial by GE
• ARINC Protocol Tutorial by Condor Engineering
• ARINC Protocol Tutorial by Alta Data Technologies