Can anyone please elaborate me of ARINC 429 on aircrafts?

Question

These ARINC 429 are used as system integration for EFIS or Electronic Flight Instrument System. The crosstalking of computers and for system testing (BITE) or Built-In Test Equipment.

Answer 1

Technical Description

ARINC 429 is a two-wire data bus that is application-specific for commercial and transport aircraft. The connection wires are twisted pairs. Words are 32 bits in length and most messages consist of a single data word. The specification defines the electrical and data characteristics and protocols. ARINC 429 uses a unidirectional data bus standard (Tx and Rx are on separate ports) known as the Mark 33 Digital Information Transfer System (DITS). Messages are transmitted at either 12.5 or 100 kbit/s to other system elements that are monitoring the bus messages. The transmitter is always transmitting either 32-bit data words or the NULL state. No more than 20 receivers can be connected to a single bus (wire pair) and no more than one transmitter.

[edit] ARINC 429 Word Format

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

    * Bit 32 is the parity bit, and is used to verify that the word was not damaged or garbled during transmission.

    * Bits 30 to 31 is the Sign/Status Matrix, or SSM, and often indicates whether the data in the word is valid.

          o OP (Operational) - Indicates the data in this word is considered to be correct data.

          o TEST - Indicates that the data is being provided by a test source.

          o FAIL - Indicates a hardware failure which causes the data to be missing.

          o NCD (No Computed Data) - Indicates that the data is missing or inaccurate for some reason other than hardware failure. For example, autopilot commands will show as NCD when the autopilot is not turned on.

                + The SSM can also indicate the Sign (+/-) of the data or some information related to it like an orientation (North/South/East/West).

    * Bits 11 to 29 contain the data. Bit-field, Binary Coded Decimal (BCD), and two's complement binary encoding (BNR) are common ARINC 429 data formats. Data formats can also be mixed.

    * Bits 9 and 10 are Source/Destination Identifiers (SDI) and indicate for which receiver the data is intended or more frequently which subsystem transmitted the data.

    * Bits 1 to 8 contain a label (label words), expressed in octal, identifying the data type.

Answer 2

ARINC 429 can be and is transmitted on simple twisted pair wires that are shielded. The shield is connected to aircraft ground to prevent noise interference from other sources.

We have a lot of this on the military aircraft, but we also use 1553 data bus that uses couplers and triax cable. This system allows multiple units to communicate on the same line, minimizing the amount of wiring. It also features an A and B bus, in case one fails.