How Single, Dual, and Four-Channel 1553 Make the Standard More Versatile
MIL-STD-1553 is probably the most revolutionary military standard for serial bus communication in avionics. Since its publication in the early 1970s, by and of itself, the standard has been used in a broad range of applications. Mostly in on-board data handling (OBDH) subsystems in both military and commercial applications, its support for multiple channels and dual redundancy has elevated its appeal in avionics engineering, defense, and digital/analog data communication in general. Although today’s systems prefer dual-channel 1553 and four-channel 1553 standards, it is a good idea to go back in time and study how the multi-channel support improves its functionality and features to a wide extent.
Here’s a quick look at one-channel 1553, two-channel 1553, and four-channel 1553 and their importance in serial bus communication.
But before that, let’s understand the basic features that govern this functionality.
Redundancy in MIL-STD-1553 Channels
In MIL-STD-1553, all channels usually provide dual-redundant or tri-redundant buses. This means in addition to a primary bus (bus A), there are secondary buses (bus B, bus C) which can be used in times of failure. They help implement failover capability and prevent the system from halting data transmission.
If an error is detected on the primary bus – anything from the bus controller to a remote terminal, bus monitor, or a bus terminal – the secondary bus can still salvage the situation and resume the communication. In such a case, the secondary bus is capable of everything that the primary bus was when it was faultless.
Although each channel has two buses, they do not allow operation simultaneously. Bus B will only be activated if bus A is at fault. Which makes us turn to multi-channel support for MIL-STD-1553. There are times – in all applications – where you need to divert data into two or more subsystems. And that is where 2-channel and 4-channel 1553 come into the picture.
Channel Support in MIL-STD-1553
The need to concurrently activate multiple streams of data communication using a single module (PCI Mezzanine Card (PMC), for instance) gave rise to the installation of more channels on the 1553 model. Here are a few more advantages of using multiple channels –
- Cost reduction – as only one unit is required for connection with multiple systems
- Low power consumption – one unit means less power consumption that two separate units
- Easy programmability – only a single unit has to be programmed to divert data into two different systems
For example, dual-channel 1553 can be attached to a surveillance computer through Ethernet and also to a simulation board for error detection and correction. These can be activated simultaneously and with full capability. The PCI Express bus is perhaps the most common MIL-STD-1553 multi-protocol card that enables in test and simulation activities.
Here’s a quick comparison between 1553 equipped with a different number of channels and their possible applications.
Single-channel 1553 can only allow a single operation at a given period of time. For example, consider onboard the International Space Station (ISS) where the serial data buses following the MIL-STD-1553 protocol is supposed to be responsible for connecting of different modules (advanced extremely high frequency satellite (AEHF) communicator, for instance) of the various countries.
However, due to the lack of additional channels, more standalone systems have to be installed. Which is why single-channel 1553 are used in civil applications such as commercial aerospace where information from an aircraft is downloaded into a subsystem prior to take-off for cross-checking purposes should it experience any issues while flying.
It allows for collaboration between different countries onboard the ISS. In the example mentioned above, the AEHF communication system can be connected to modules of various countries – so that each of them receives the same data. This is why there is a need for multiple channels.
Since both the channels are either transformer-coupled or direct-coupled and are capable of full programmability, they can be used to parse data to two different modules at the same time. This considerably reduces the pressure on the system CPU (while reducing power consumption) and ensures that the transmission-reception connections do not interfere with the functionality of associated I/O boards.
Some of the most common applications of dual-channel 1553 are:
- Navigational aids in commercial and military aircraft
- Stores management
Very low power dissipation and sustainable in air-cooled environments, four-channel 1553 protocols are hybrid versions of dual-channel 1553. They are majorly used in avionics where a single module has to be connected to multiple subsystems to generate periodic vital information.
The chief difference between dual-channel 1553 and quad-channel 1553 is the power system. Even though the form factor has been taken into consideration, the protocol needs a high-energy supply to handle transmission in four channels concurrently. Which is why they are only preferred in military, weapons-grade, and space applications
Following are some of the systems that four-channel 1553 are routinely used in:
- Lockheed F-117 Nighthawk Stealth Attack Aircraft
- Boeing F-15 Eagle Tactical Fighter
- Airbus A350-XWB Wide Body Jet Airliner
- FMG-148 Javelin Anti-Tank Missile
- AGM-65 Maverick Air-to-Ground Tactical Missile
- XM2001 Crusader Self-Propelled Howitzer
- Advanced Extremely High Frequency (AEHF) Satellite
The arrival of eight-channel 1553 again puts the onus on the 40-year old military standard protocol and shows us that it is still a powerful and relevant piece of technology. While the channel usage depends on the applications it is being used in, one thing is clear that MIL-STD-1553 is not going away.
It should also be noted that MIL-STD-1773 is also making a comeback in electronics and telecommunications fields owing to its high-quality reception and transmission. Engineers prefer to use optical cabling to ensure that power wastage is minimal and the data is not stolen, especially in military-based applications.
Multi-channel 1553 helps, in those cases, where one channel might be used as a dummy and the infiltrator have to guess what channel the real data is being transmitted on. In this regard, 4-channel 1553 is the most used protocol in the 21st century.
MIL-STD-1553 also supports a large range of data boards and subsystems, which is why it is still the number one protocol in serial data communication. For example, EXC-1553ccVME/Px(S) is a 16-channel interface board for 1553 and is used for conduction-cooled VME systems