Military aircraft come and go, but Mil-Std-1553 soldiers on. This deterministic bus has remained fresh by constantly adopting the latest packaging technologies.
The Mil-Std-1553 data bus market continues to thrive despite the military's long-term emphasis on higher-speed systems. The addition of more memory, new packaging technologies, faster terminals, and multiprotocol cards is helping industry to support the demands of this still commonplace legacy bus.
An obvious approach to performance enhancement is to increase available memory. "When our clients buy a Mil-Std-1553 card, they want to be sure it has enough processing and memory to accommodate the application they intend," says Doug Ullah, director of sales and marketing for the German bus specialist, AIM GmbH. AIM supplies 1553-compliant test and simulation cards and software in form factors including PCI, Compact PCI (CPCI), VME, PMC, PCMCIA and ANI.
Flight hardware is adding random access memory (RAM), too. National Hybrid's Preferred Terminals series employs the same footprint as its legacy series of terminals (0.95 inch square), but all Preferred Terminals have 64K-words of RAM, whereas the legacy terminals ranged from 4K-words and 16K-words to 64K-words. "Years ago [the terminals] didn't need so much RAM," says Roy Nardin, National Hybrid co-president. "But as the bus handles more messages and message types, larger RAM becomes important, especially in the bus controller and bus monitor."
Bohemia, N.Y.-based Data Device Corp. (DDC) also provides a range of RAM content. Its Simple System Remote Terminal (SSRT) contains 32-words of RAM, while its ACE products range from 4K-words x 16 (8 Kbytes) to 64K-words x 16 (128 Kbytes).
DDC offers an extensive line of commercial/military off-the-shelf (COTS/MOTS) Mil-Std-1553 cards, components and software. "In the past the military wanted full mil-temp, hermetically sealed, highly reliable military components," says Mike Hegarty, DDC's data bus technologies product marketing manager. The whole COTS initiative has changed that way of thinking, however.
"Best commercial practices have been found to work in military systems, so there's no longer this need to have specialized military components for most applications." DDC's MicroACE line of 1553 products takes advantage of commercial packaging technologies, including injection-molded plastic encapsulation, and it meets most environmental humidity and life test requirements. For harsher environments DDC still offers the ACE series of hermetically sealed ceramic components.
Several companies have introduced high-speed cards and terminals to support the military's new enhanced bit rate (EBR) specification and the miniature munitions system interface (MMSI) specification expected to be released soon. The resulting EBR-1553/MMSI components run at 10 Mbits/s vs. the standard 1553 1 Mbit/s, but are not compatible with legacy 1553 cabling.
Mil-Std-1553 stalwart, Holt Integrated Circuits, meanwhile, has announced the availability of the HI-6110, a single-chip, 3.3-volt, CMOS protocol device. Implementing the 1553B (Notice 2) protocol between a host processor and a dual-redundant 1553 bus, the HI-6110 boasts less than 500-mW power consumption at 100 percent duty cycle. The integrated circuit includes onboard, dual-redundant transceivers, as well as Manchester encoder/decoders, 1553 message-level protocol engine, and sufficient on-chip data storage for single message buffering. It can be configured as a bus controller, remote terminal, addressed monitor terminal or non-addressed monitor terminal.
According to Condor Engineering's 1553 product manager, Bill Schuh, Condor was the first with an MMSI board. Schuh advocates using standard 1553 for flight control and EBR-1553/MMSI for non-flight related systems. "For virtually all true command and control flight control applications, 1 Mbit/s is enough," Schuh says. "Part of the reason we're seeing [higher speeds] is the mission systems that have nothing to do with the flight control: radar systems, firing capability, and non-flight related sensors. There's where you get into the huge bandwidth needs that are being developed."
National Hybrid, in Ronkonkoma, N.Y., produces 10-Mbit/s terminals for the EBR-1553/MMSI market but also produces 2-Mbit/s terminals compatible with legacy 1553 cabling. According to Nardin, the 2-Mbit/s terminals allow customers to double the data rate and/or terminals on a standard 1553 bus without rewiring the airplane.
"Our bus controllers are capable of sending messages at either the 2-MHz rate or the 1-MHz rate on a message-by-message basis, controlled by the software," Nardin says. "You can have both 1-MHz and 2-MHz terminals on the same bus for subsystems that require the higher speed or if you just run out of addresses and need more terminals."
Nardin explains that a 1-Mbit/s terminal can transparently share the same address as a 2-Mbit/s terminal, and the bus controller will only send messages of the appropriate data rate to the corresponding terminal. This nearly doubles the effective number of 1553 terminals to 60 without a second bus controller. The "overclocked" 2-Mbit/s terminals use the same software and interface as 1-Mbit/s terminals and can be placed on standard 1-Mbit/s PMC and PCI cards.
Some customers are demanding versatile implementations. Combining different functions or protocols on the same card or terminal can save inventory costs.
National Hybrid's enhanced terminals can be programmed to function as bus controllers, remote terminals, bus monitors, or simultaneous bus monitor and remote terminal. When programmed in this last configuration, the terminal operates as a bus monitor for all terminal addresses and as a remote terminal for one discrete terminal address. According to Nardin, this is most useful as a backup bus controller, but the terminal's versatility also allows the customer to inventory fewer part numbers.
AIM also provides versatility in its Common Core hardware design cards for the test and simulation market. The base design uses the same elements and hardware components (bus interface unit [BIU] processors, global memory and application support processor), but the board firmware can be flash-programmed for different protocols, including Mil-Std-1553, ARINC 429, AFDX/ARINC 664, Stanag 3910 and Panavia serial. This allows the customer to use the same board for testing different interfaces, although the physical bus interface must be changed out to adapt to the specific data bus interface standard.
AIM's generic carrier cards for VME and CPCI offer one or two PMC sites, providing more than one protocol on a single module, such as Mil-Std-1553 in combination with ARINC 429. AIM's PBA.pro software allows the user to monitor the activity of multiple avionics buses and protocols simultaneously. This is appropriate, as many aircraft, like the Airbus A400M tactical transport, have multiple bus architectures.
Test and Simulation
Another driver of multiple-protocol components is the confluence of military and commercial technologies, observes Kevin Christian, customer services manager for Washington State-based Ballard Technologies.
ARINC 429 and Mil-Std-1553 are being implemented in systems for a number of reasons, such as a military aircraft's use of commercial satcom, Christian says. Ballard's OmniBus product--typically used for test and simulation but occasionally included in non-flight critical, embedded applications--can perform the conversion automatically, bringing in the 1553 data, reformatting it and pushing it out as ARINC 429 data. Another dual-protocol example that Christian has seen in development is airliner missile defense, where an aircraft uses an ARINC 429 data bus to send navigation information to the 1553-based missile defense sensors.
The OmniBus series of interface cards, available in PCI, CPCI, and VME, includes a Power PC processor preloaded with Ballard's own version of the Linux operating system. "Our OmniBus boxes are essentially entire computers in a box," Christian says. "You can move your application over to the box itself, and now the host computer no longer has to be involved.
Condor's modular solutions, meanwhile, combine several different protocol mezzanine cards onto a single board. Available in IP, PCI, CPCI, VME and VXI platforms, the products allow a combination of 1553, ARINC, RS-422 and other protocols, taking up only one slot on the host computer.
AIM recently delivered its fourth-generation PCI-X cards for Mil-Std-1553 applications. "This card has more performance, including one or two 400-MHz XScale processors for the BIUs and an additional 400-MHx Intel IOP application support processor," Ullah says.
Data Bus Products, Manhasset, N.Y. offers several bus couplers for connecting test and simulation equipment to the bus. The flange-mounted couplers range from single- to eight-stub models. Data Bus Products also offers one- to four-stub inline couplers.
Condor, DDC, National Hybrid and AIM supply PMC cards for embedded on-aircraft solutions. Condor's embedded product line includes: the QPMC-1553 multichannel card, containing simultaneous bus controller, bus monitor and 31 remote terminals; the Q104-1553 PC-104 Plus interface card; and the intellectual property (IP) Core-1553 and Core-MMSI protocol cores, compatible with both field programmable gate arrays and programmable logic devices.
California-based Actel Corp. also offers a multifunction 1553 IP core with bus controller, remote terminal and bus monitor functionality, called the Core1553BRM.
DDC provides IP cores based on its MicroACE designs. The DDC core includes the memory management unit found in the company's enhanced MiniACE series of devices. "We've really fine-tuned that memory management unit so some of the real-time burdens normally associated with the software that controls this interface are gone," Hegarty says. "I've seen mission computers running 800-MHz Power PC processors brought to their knees trying to service Mil-Std-1553 1-Mbit/s interfaces because there's not enough offload in the devices." An SSRT core is also available for applications that don't need the memory management function to interface to a processor.
Beta Transformer Technology Corp., a subsidiary of DDC, recently completed qualification testing on its single- through six-stub 1553 data bus box couplers based on airframe industry guidelines and Mil-PRF-21038. Designed for embedded solutions, the couplers operate in temperatures ranging from -55 to 130 degrees C, and use fully screened, military standard transformers to ensure reliability and waveform integrity in all 1553 applications.
North Atlantic Industries, also of Bohemia, recently released a three-module, multifunction, single-slot VME communications card for embedded applications. The 64DI VME unit allows the customer to incorporate up to three different protocols, including 1553, RS-232C/RS-422/RS-485, Profi-bus, discrete input/output and transistor-transistor logic (TTL).
Ohio-based ITCN recently was awarded a General Services Administration contract to provide its SystemTrace line of synchronized instrumentation to U.S. government users. SystemTrace is essentially an Ethernet-connected control network that provides real-time, non-intrusive monitoring of up to eight dual-redundant Mil-Std-1553 buses and multiple VME chassis simultaneously. SystemTrace software loaded on a workstation allows customers to collect and analyze time-correlated data from up to 256 buses across 32 module chassis per session.
Excalibur Systems' EXALT (Excalibur Analysis Laboratory Tools) data bus monitor and analysis simulation software allows users to view data from multiple bus types, including 1553, ARINC 429 and RS232/422/485, simultaneously on one graphical interface. EXALT allows users to define, monitor and display messages and engineering units, and to focus on raw data, text, graphical plots, bar charts and discrete displays.
Excalibur also produces Merlin simulation software for 1553 bus controllers, remote terminals and bus monitors. An EXALT Plus add-on acts as a bus controller simulator, allowing users to set up the bus list including minor frame timing, error injection and retry parameters. The company's 1553 product line includes PC, PCI, CPCI, PMC, PC 104, VME, VXI and PCMCIA formats.
High-end development and integration testers include the military bus, as well. TechSat's ADS2 System Integration Bench, for example, supports Mil-Std-1553, along with AFDX, ARINC 429, CANBus, discrete and analog.
Israel-based Ampol provides PC-based bus monitor and simulation software. Ampol's dataMARS software passively monitors, displays and records avionics data from numerous avionics data formats, including Mil-Std-1553, ARINC 429, PCM, Ethernet, video, voice, analog and digital signals. The company's dataSIMS software generates real-time avionics data for rapid emulation of designed units on a live bus, or for controlling other units through their communication buses and signal lines.
YED USA produces a handheld diagnostic tool called the DATAIR-1500/SR. This 1553 data monitor provides data analysis and diagnostics, including instantaneous bus traffic, polling rates, non-responding remote terminals, low word counts, and other data, without need for a separate PC.
UK-based BCF Designs, meanwhile, produces a Mil-Std-1553 data bus network/harness tester that isolates all common wiring faults (short circuits, shorts to shield, open circuits and crossovers, etc.) on the aircraft. The tester records insertion loss between any two stubs in decibels. BCF claims the S2476N is the only tester that can footprint a 1553 data bus, allowing users to monitor system integrity and schedule preventative maintenance.
Future Still Bright
The 1553 industry is holding its own, according to National Hybrid's Nardin, who estimated that 1553 would be in use "for at least the next 20 to 30 years," thanks to new platform design-ins.
"No bus gives you the reliability and the safety of 1553, which is why [the military] still uses it for command and control and for munitions," Nardin says.
The quest for 200-Mbit/s throughput over existing 1-Mbit/s Mil-Std-1553 cabling may finally have turned a corner, U.S. Air Force researchers say. Driven by the need to solidify a new, high-speed standard in advance of a large airborne Joint Tactical Radio System (JTRS) card procurement, the military plans to publish Mil-Std-1553B (Notice 5) by January 2006. Edgewater Computer Systems Inc., the Canadian company whose technology is making the new standard possible, is providing "technical inputs" to the effort under an Air Force contract. Edgewater technology will be flight tested on an F-16 early next year.
Basic requirements under the standard are:
200-Mbit/s throughput over existing cabling;
10-12 bit error rate;
Simultaneous operation with legacy 1553 on a non-interference basis;
328-foot (100-m) cable lengths; and
Mil-Std-461 performance thresholds.
Not to be outdone in the high-speed arena, Data Device Corp. (DDC) has demonstrated 100-Mbit/s capability in a lab over existing cabling. The company has announced no timeline for release of high-performance 1553 products.