What Is MIL-STD-1553?

MIL-STD-1553 is the US Department of Defense standard for a serial data bus that connects the subsystems of a military aircraft or vehicle. Its full title is Aircraft Internal Time Division Command/Response Multiplex Data Bus. The first version appeared in 1973 for the US Air Force, and the F-16 was the first major aircraft to use it. MIL-STD-1553A followed in 1975 and MIL-STD-1553B in 1978, and 1553B, amended by later notices, is the version in service. NATO publishes the same bus as STANAG 3838, and the USA as Def Stan 00-18 Part 2.

The bus is command/response. One bus controller starts every transfer, and the remote terminals on the bus only ever answer it, so two devices never talk at once and timing is fully predictable. Data moves at 1 Mbit/s in both directions, one message at a time, using Manchester II bi-phase encoding, which carries the clock in the signal. Most installations run two complete buses, A and B, so traffic can switch to the second bus if a cable or coupler fails.

Because every device hangs off a shared cable, a 1553 network is a classic bus topology network, terminated at each end to match the cable’s impedance.

A MIL-STD-1553 system is built from four kinds of part.

Everything on the bus travels as 20-bit words: a 3-bit-time sync pattern, 16 bits of content and an odd parity bit. There are three word types. A command word from the bus controller carries the remote terminal address, a transmit or receive bit, a subaddress and a word count. A status word is the remote terminal’s reply, with flags for errors, service requests and busy conditions. A data word carries 16 bits of payload, and one message holds up to 32 of them.

Messages are combined into a few formats: bus controller to remote terminal, remote terminal to bus controller, remote terminal to remote terminal, mode commands for bus management, and broadcast. The bus controller runs them in repeating minor and major frames, so each parameter is refreshed at a fixed rate.

The 1553 bus is often compared with the commercial ARINC 429 bus, with CAN and with Ethernet-based avionics networks. The differences come down to speed, direction and who controls access.

Ethernet offers far more bandwidth but is not deterministic by default, which is why avionics versions such as AFDX add fixed bandwidth allocations. Newer military vehicles increasingly use Ethernet as the main network, for example under the UK’s Generic Vehicle Architecture, Def Stan 23-009, while keeping 1553 for existing subsystems.

The case for 1553 is predictability and redundancy. The bus controller fixes the schedule, so latency is known in advance. Dual buses and transformer coupling keep traffic flowing through a damaged cable or a failed terminal, and the differential signal resists noise. Fifty years of service mean parts, test tools and engineers who know it are easy to find.

The challenges are bandwidth, weight and age. 1 Mbit/s cannot carry video or large sensor data, the cable and couplers add weight, and qualified parts cost more than commercial networking. The protocol has no built-in authentication, which now matters in security reviews, and higher-speed schemes that run over existing 1553 wiring have been developed to extend older aircraft.

MIL-STD-1553 is still very much in use. It links subsystems on fighters such as the F-16 and, as STANAG 3838, the Eurofighter Typhoon, on attack and transport helicopters, on armoured vehicles, on many satellites and on the International Space Station. Upgrades to these aircraft and vehicles keep 1553 interfaces in demand.

A computer joins a 1553 bus through an interface card that can act as bus controller, remote terminal or bus monitor, often all three on one channel. Cards come in PCIe, Mini PCIe, PMC and XMC, PC/104 and USB formats, with one to four dual-redundant channels and hardware time-tagging. Typical hosts are mission and display computers, test benches, simulators, data recorders and ground support equipment.

In a vehicle or aircraft the host has to meet the same environment as the rest of the system: shock, vibration and temperature, electromagnetic compatibility and the vehicle’s power supply, which for ground vehicles is defined by the MIL-STD-1275 vehicle power standard. Our guide to US military standards explains how these fit together. Our military computers list MIL-STD-810H and MIL-STD-461 compliance, and our military and aerospace computing page covers the wider range.

We build rugged and military computers with the slot, power and I/O a 1553 interface card needs, fit the card your program specifies, install the drivers and test each channel before the system ships. Tell us your channel count, card format and installation, and we will specify the computer to match.