Avionics Data Bus
A bus is a data highway that links one LRU (Line Replaceable Unit) to another. In earlier avionic systems, communication cables are used to transmit the data. To transfer a bit of data at least one pair of wires is needed for each signal. These wires transmit information over a single twisted and shielded pair of wires (the databus) to all other system elements having need of that information (up to as many as 20 receivers). A data bus connects all the internal components of the computer to the CPU and main memory. When referred to as an aircraft, it is the data highway that links one computer to another aircraft like the FMC (Flight Management Computer) and the ADC (Air Data Computer).
What are the types of avionics data bus?
Based on the type of connection data buses are classified into two types. They are serial bus and parallel bus.
- Serial Bus: As the mentioned in the name, each bit of the data word is transferred via the same wire. Only one bit of word is sent at a time. Examples of serial data bus are PCIe, USB, ARINC, I2C, etc.
- Parallel Bus: In this type, each bit of the data word is transferred via a specific wire. It requires a lot of wiring. Examples of parallel bus are conventional PCI.
Which type of data bus is better, serial or parallel?
Parallel buses should have been faster than serial data buses. But, there are many issues in using parallel data buses. Such as, parallel buses suffer from clock skew. It means a bit of data can reach the destination before or after other bits. It causes lack of synchronization in parallel data buses. Also, the no of wires used in the parallel data bus is more than the serial data bus. Also, parallel data buses are not synchronized as fast as the serial data buses results in low data rate.
What are the types of serial digital data transmission?
Common serial digital data transmissions are two types. They are single source-single sink and multiple source-multiple sink.
- Single Source-Single Sink: It is the earliest application that contains a dedicated link. One LRU (line replaceable unit) communicates with a single LRU. Example: Sea Harrier and Tornado aircraft.
- Single Source-Multiple Sink: In this system, one LRU transmits data to multiple LRUs at a time. ARINC 429 is the example for this type.
- Multiple Source-Multiple Sink: In this system, multiple computers transmit data to multiple LRUs at a time. This is also known as full duplex and is widely used by military users. Example: MIL-STD-1553B and ARINC 629.
Why avionics data buses are created in such a way?
In 1950s and 1960s, communication between two stations is done through a lot of wires without a bus. It makes very difficult for the installation and also for the modification. The parts of these systems are elctro-mechanical which are heavy and requires large space. After that digital systems are used to transmit the data. They are also heavy, slow and difficult to reprogram. Each component of the system contains its own computer and memory. They use a bus between components limiting the usage of more wires.
What are the major avionics data buses?
Many commercial and military aircraft utilize many avionics data bus technologies. The major avionics data buses are MIL-STD-1553, ARINC 429, ARINC 629.
- ARINC 429 defines how avionics equipments and other systems communicate on the aircraft. It is a unidirectional broadcast bus (simplex). The highest speed of data transmission is 100kbps and the least is 12 to 14.5kbps. It is a low weight and low cost with high reliability.
- MIL-STD-1553B is a serial time division command response data bus. It has a bit rate of 1Mbps. It is a military half-duplex protocol.
- ARINC 629 is used in Boeing 777. It is a multi-transmitter data bus. It is half-duplex with a bit rate of 2Mbps. The data is transferred using electromagnetic induction between two or more systems.
What are the problems a data bus solves?
Data buses solve many problems. They are:
- ARINC 429: It is developed to promote interoperability between devices on civil aircraft. Designed to connect a single transmitter to 10 receivers. Messages are expected to be transmitted between once and up to 50 times a second. Receivers receive their data simultaneously which accomplishes the synchronization.
- MIL-STD-1553B Designed to connect up to 32 devices with the ability to transmit 16-bit words of data in a message. Simultaneous transmission by multiple devices is prevented. Synchronization is accomplished by using a Synchronization Mode Code.
- ARINC 629: Published in 1990. It is intended to work in concert with ARINC 429. It is an attempt to reduce the wiring complexity inherent in the point-to-point ARINC 429 architecture. Facilitates the transfer of non-periodic data such as databases or video. Designed to connect up to 120 devices and be able to transmit strings of up to 256 sixteen-bit words with a speed of 2MHz. Simultaneous transmission by multiple devices is prevented by a set of timers in each device along with the ability to detect transmission on the bus.
- Actel. 2009. "ARINC 429 Bus Interface." Actel, October 07. Accessed 2022-07-22.
- Ahmed Murad, Mirza Masroor. 2019. "DATA Bus and interface with avionics." LinkedIn, October 20. Accessed 2022-07-17.
- Benzinga Staff. 2014. "SAE International Completes Asset Purchase of ARINC Industry Activities – Expands Aerospace Portfolio." Benzinga, January 13. Accessed 2022-08-11.
- Electra IC. 2014. "MIL-STD-1553B vs MIL-STD-1553C." Electra IC, February. Accessed 2022-08-06.
- Haber, Gary. 2013. "Arinc's new owner to sell off two subsidiaries." Baltimore Business Journal, December 24. Accessed 2022-08-06.
- Ipapadop. 2013. "Data Bus." Slideshare, July 01. Accessed 2022-08-01.
- Koppel, David. 2017. "Why are there so many avionics communications specifications?" Excalibur Systems, June 08. Accessed 2022-08-04.
- Military Aerospace Electronics. 2007. "The coming revolution in commercial avionics data networking." Military Aerospace Electronics, February 01. Accessed 2022-08-06.
- Nour El-Din Safwat. 2014. "The Evolution of Aircraft Data Networks." International Journal of Computer Applications, May. Accessed 2022-08-06.
- Ostroumov. 2012. "Avionics Digital Data Buses." Slideshare, September 18. Accessed 2022-08-01.
- Punia, Dheeraj. 2021. "ARINC 629 Digital Data Bus Specifications." Logic fruit technologies, January 18. Accessed 2022-07-22.
- Punia, Dheeraj. 2021a. "A swift introduction to MIL STD 1553B Bus Architecture." Logic fruit technologies, March 12. Accessed 2022-07-25.
- Punia, Dheeraj. 2021b. "ARINC: The Ultimate Guide To Modern Avionics Protocol " Logic fruit technologies, October 21. Accessed 2022-08-06.
- Wikipedia. 2021. "ARINC 629" Wikipedia, December 08. Accessed 2022-08-06.
- Wikipedia. 2022. "MIL-STD-1553." Wikipedia, June 02. Accessed 2022-08-06.
- Wikipedia. 2022a. "ACARS." Wikipedia, May 28. Accessed 2022-08-06.
- Wikipedia. 2022b. "ARINC 424." Wikipedia, February 15. Accessed 2022-08-06.
- Wikipedia. 2022c. "Serial Communication." Wikipedia, May 15. Accessed 2022-08-27.
- Yasir. 2016. "Avionics Buses." Slideshare, December 24. Accessed 2022-08-01.
- Nour el-din Safwat. 2014. "The Evolution of Aircraft Data Networks." Research Gate, May. Accessed 2022-08-27.
- Keller, John. 2007. "The coming revolution in commercial avionics data networking." Military Aerospace Electronics, February 01. Accessed 2022-08-27.
- Chen, Dan-qiang. 2013. "Research on Key Technologies of Detecting 1553B Avionics Data Bus Network." Science Direct, October 23. Accessed 2022-08-27.