Channels of information exchange (Data Bus - DB) is provide interaction of avionics components, subsystems, blocks, modules with each other and with other equipment on board of computer.
Channel information exchange - a set of tools that provide interaction of components of the system. In a general sense Data Bus - a set of logical and physical principles of interaction of system components; or a set of rules, algorithms, time synchronization for data exchange between these components, and a set of physical and functional characteristics of the connection that implement such interaction .
There are many different types of Data Bus, differing own characteristics and principles of exchange data.
Cnannels of Data Bus are used at different structural levels:
- Inside of computing units for connecting devices and functional modules;
- Inside of system for information exchange between units (LRU, LRM);
- To connect to systems of different sensors (analog and digital)
- To exchange information between different systems.
At each of these levels used different Data Bus, optimized to perform specific functions for such level.
For develop and build LRU or LRM manufacturer may use any standard DB. Various modern electronic components supporting different standard DB, but in general, DB choice depends on the selected microcontroller.
At a higher level for the exchange of information between different systems and units used specially designed standardized DB. They must satisfy such requirements :
- To support the exchange of information in real time;
- to ensure high noise immunity;
- to be resistant to failure (breaking, locking, module attached waiver should not lead to complete failure);
- delay transmission of information must be deterministic and rather small;
- to ensure operation in the event of various environmental influences;
- to controll the state of DB;
- to provide flexibility (change modules should not lead to significant changes in other blocks of the system);
- to satisfy the requirements of IMA.
In connection with these requirements for information exchange between systems onboard aircraft used specially designed channels of information exchange.
The historical development of architecture building channels of information exchange between different systems shows in Fig. 16.
Fig. 16. The historical development of Digital Data Buses
From the beginnings of the avionics system each stirred in a special place for one. Information from one system to another transmitted via analog data channels. It required a large number of wire connections between the blocks. In addition, analog DB had a very low noise immunity. To solve these problems, in 1974 the US military developed the first digital channel data (Digital Data Bus - DDB) MIL-STD-1553  and introduced it for intersystem exchange. Later appeared standard ARINC 429 for use in civil aviation, which is still used by manufacturers of avionics . However, the use of digital channels to exchange data between separate systems is not increased functionality and flexibility of the systems.
Federal concept of building avionics systems allow to combine modules and blocks in certain "federation" with one bus for data transfer. With the help of special modules tires "federations" , the system was cooperating in a global network of aircraft. The development of avionics needed to create new standards faster DB. Military modernized MIL-STD-1553B and based on it created STANG 3910. In civil aviation was selected a fundamentally different direction and created a new standard ARINC 629.
Increasing the number of avionics and rising of computing capacity of computer equipment needed very close integration of different systems and avionics units at different levels of functioning. It was the reason of development and use of IMA.
Requirements of capacity of Digital Data Bus continues to steadily rise. It’s happened, because avionics systems got new tasks which needed of transmission of large data streams in real time. As a result, began to appear superfast Digital Data Bus (STANAG 7076, Fiber channel, AFDX).
The main types of digital information transfer:
- One source - one receiver. This is one of the easiest Digital Data Bus, which transfers data from one piece of equipment to another.
- One source - many receivers. Describes the technology of transfer information from one block to a certain number of other (ARINC 429).
- Many transmitters - many receivers. These Digital Data Bus has few or more transmitters that can transmit information to a certain number of receivers (MIL-STD-1553B, ARINC 629).
On the board of modern aircraft using many different channels of information exchange, within blocks of avionics components, simple interfaces for communication with sensors and complicated to build Digital Data Bus Communication systems together.
Introduction Digital Data Bus required standards development for them. Creating uniform standards allowing manufacturers to build different interchangeable blocks that could communicate with each other.
The basic standards for the digital channels of information sharing :
- The standards developed by the Association of designers moving vehicles (SAE):
- AIR 1189 – medium-speed Digital Data Bus time division (for multiplex systems);
- AIR 4013A - multiplexed Digital Data Bus (for MIL-STD-1760 series);
- ARP 4258 - Digital Data Bus low-speed discrete signal interface;
- AS 15 531 - digital time division multiplexed Digital Data Bus (request / response);
- AS 4074.1 - Digital Data Bus multiplexed with direct access;
- AS 4075 - ultra fast ring Digital Data Bus;
- AS 4710 - parallel interface Digital Data Bus (Pi-Bus);
- AS 5370 - duplex multi optic-fiber Digital Data Bus;
- AS 5643 IEEE-1394b - digital DB for military and aerospace products.
- Standards developed by ARINC:
- ARINC 429 - Digital Data Bus to maintain the connection type "point - point" two wires, bipolar;
- ARINC 573 - Digital Data Bus registration system for flight information;
- ARINC 629 - Digital Data Bus data simultaneously from several transmitters;
- ARINC 659 - Digital Data Bus for IMA;
- ARINC 664 - description of AFDX;
- ARINC 708 - Digital Data Bus to transmit graphic information from the board to the meteo radar display system;
- ARINC 818 - Digital Data Bus to transmit uncompressed video, audio and text information.
- The standards developed by IEEE:
- IEEE-std-1149.5 - digital DB for testing equipment;
- IEEE-std-1393 - digital fiber-optic DB for spacecraft;
- IEEE 1355.2 - digital DB with the low transmission.
One of the most perspective digital standard DB is simple to organize networks Ethernet, adapted for use on board computer (Avionics Full Duplex Switched Ethernet - AFDX) , which provides high speed data transfer. Ultra-fast ASCB standards for aircraft and private aircraft CSCB provide super-fast data transfer in duplex mode . In some cases, it’s reasonable to use CSDB - low-speed, bidirectional Digital Data Bus, built based on RS-422.
Comparison of basic standards for Digital Data Bus on speed data shown in Fig. 17.
Fig. 17. Comparative analysis of diferent Digital Data Buses