ARINC 429 – Wikipedia

ARINC 429 is a data bus standard for commercial aircraft developed in the 1970s and introduced in the 1980s. A distinction is made between a high-speed and a low speed bus. With a high-speed bus, the maximum data transfer rate is 100 kbit/s, at LowSpeed ​​12.5 kbit/s.

There are other protocols according to the ARINC standard. ARINC 429 can be found in one Light -Avarians also in business and sports aircraft again. In the military aviation and space travel, the MIL-STD-1553 bus is preferably used instead of the Arinc bus.

Timing diagram on the ARINC-429 interface

In principle, the serial interface ARINC-429 is comparable to the differential EIA-422 interface. Only three have been defined instead of two different levels (+10 V, 0 V and −10 v). How individual bits are transmitted can be seen in the presentation of the resulting difference signal (ARINC-429-timing).

It is characteristic of each bit that the level has the voltage ± 10 V for half of the time and then in the other half 0 V (RZ code). So synchronization information is available for every bit. An asynchronous interface z. B. RS-232 requires a start and stop bit for comparison for each data word.

Communication is a 1-to-N connection (a transmitter, n recipient). Due to the high voltage level, the same restrictions apply regarding the line length and transmission rate as with RS-232 and RS-422. Therefore, quite moderate transmission rates of either 12.5… 14.5 or 100 kilobits/second are defined. In the low-speed operating mode, tolerances of 10% and the high-speed mode of 5% apply to the transmission rate.

In order to create no interference signals through the transmission, there is a so -called slope control. This means that the climbing and waste flanks are as flat as possible according to the transmission rate. Since there is no start-bit, a 32-bit data word is recognized over a break of at least 4 bits, in which no signal lies (Sync Gap: Minimum 4 Bits). Only one GAP of max. 2 bit periods is allowed within the 32 data bits. And at the end of the data word, a GAP of at least 4 bit periods is again defined.

Data transmission in ARINC 429 is generally carried out in a fixed frame with a fixed length of 32 bits. The transmission of each frame begins with bit 1 and ends with bit 32, but the description in the standard always follows the direction of bit 32 to bit 1, i.e. in the opposite direction such as the individual bits are physically transferred. Each frame is divided into five areas that are assigned to certain bit positions within the framework. These are:

• Bit 32: Parity bit over the entire framework
• Bits 31 to 30 positions Sign/Status Matrix (SSM) of the framework. In this, certain conditions are generally encoded:
  • Normal Operation (No) – indicates that the data in the data field is accepted as correct.
  • Functional Test (FT) – indicates that the data in the data field is transmitted to test purposes.
  • Failure Warning (FW) – indicates that the data in the data field are not considered reliably or are missing in the data field due to a malfunction.
  • No Computed Data (NCD) – indicates that the data in the data field is rated as inaccurate or as questionable for other reasons as a malfunction. For example, commands or reports from the autopilot NCD marked if the autopilot is not activated.
• Bits 29 to 11 is the actual data field within the framework. It can contain bitfelder, numbers in the BCD code or as a two complement or as a combination. The meaning and shape depend on the one listed below Label .
• Bits 10 to 9 are Source/Destination Identifiers (SDI) and express either the desired reception module or the broadcast module of the frame.
• Bits 8 to 1 put this Label that describes the data type in the data field. The different and possible labels are defined in the standard.

• Cary R. Spitzer, Uma Ferrell, Thomas Ferrell (Hrsg.): Digital Avionics Handbook . 3. Edition. CRC Press, 2015, ISBN 978-1-4398-6861-4, chapter 34 (English).