Using MIL-STD-1553 to Add New Capabilities


AV-8B Harrier II

With the phenomenal power of new sensors, and the very high performance of new processing devices, there are many new capabilities that can be added to a military system that can deliver valuable information to the war fighter and keep them safe. The latest data can be provided that can have a critical impact on the mission.

But: there’s a problem. Updating an existing system to take advantage of these new capabilities isn’t a task lightly undertaken. It can be costly. It can be very time-consuming. Worst, though, is that making any changes to an existing, proven, reliable system may well be unthinkable, given that the entire system would subsequently likely need to be re-validated.

Supposing it were possible, though, to add these new capabilities in such a way that the integrity of the original system remained intact—obviating the need to perform a complete system recertification?

Monitor mode

Well: it is. The venerable 1553 protocol has a monitor—“sniffer”—mode. It allows data to be garnered from the 1553 bus within the existing system and passed to new subsystems. That data would typically be navigation data, flight data, systems data and so on that are already on the bus—and that could be of value to a new subsystem. Because it is a read-only mode—no data is written back to the system—it has, in theory at least, no ability to impact the operation of the trusted system from which it is deriving data.

Most 1553 interface cards feature a mode that allows a monitor-only capability—which would be appropriate for this type of application. In the case of Abaco Systems, we provide several mechanisms for our cards by way of user or factory control to set this up. We provide the capability to program the transmit control to a fixed transmit Inhibit if this is desired. This control forces the circuitry to a "disable" state and does not allow the on-board 1553 transceiver device to actually send data onto the data bus, thus disrupting the actual flight system data integrity.

Challenge

Of course, there is a challenge to this "no write" mode—and that is that it can not, by definition, provide feedback to the system about the data it is acquiring and routing. If, for example, data is being missed—there’s no way of telling. The challenge is to develop, test and verify complete and correct 1553 operation via some external means. That’s by no means always easy.

Above, I said that “in theory” configuring a 1553 interface card in monitor mode should have no impact on the system. There are, though, circumstances where it might. Interested in knowing more? We’ll be publishing a white paper on this whole subject—but if you can’t wait till then, please feel free to contact me via the blog. Here at Abaco Systems, we have enormous expertise in all things 1553—and we’d be delighted to work with you on your latest project.


bill.tilman@abaco.com's picture

Bill Tilman

Bill Tilman is an avionics applications engineer, and has worked in the aerospace industry – notably with MIL-STD-1553 – for over 30 years. His specialties include the architecture, design, development and test of electronic systems as well as MIL-STD-1553 training and RT validation testing. A committed fan of technology, Bill spends his spare time bicycling, hiking and camping around New Mexico, dabbling with amateur radio, working on various DIY electronics and mechanical projects.

More Posts