MIL-STD-1553 communication works by designating a single active Bus controller to manage data flow to, from, and between multiple remote terminals. The bus operates in a time-division multiplexed manner, where data is transmitted in messages consisting of “words”.
All words begin with a 3 µs “Sync” field and include a fixed number of data bits (16) and a single parity bit for error-checking each word. There are three types of words: Command words, transmitted by Bus controllers (BCs); Status words, transmitted by remote terminals (RTs); and Data words, transmitted by either BCs or RTs.
Messages are made up of a defined series of words. Different message formats allow the bus controller (BC) to send data to remote terminals (RTs), RTs to send data to the BC, or one RT to send data to another RT.
Broadcast messages let the BC or an RT send data to all RTs on the bus. Meanwhile, “mode code” messages manage bus functions and contain either no data words or just one data word.
MIL-STD-1553 Tutorial and Reference:
Here are some details about how MIL-STD-1553 communication works:
- Time Division
Only one computer terminal can transmit at any given time, while the other computers listen and receive. This is different from full-duplex systems like Ethernet and RS-232, which allow simultaneous transmit and receive on different wires.
- Bus Controller
The bus controller is the only device that can transmit command words, which initiate all messages. Command words contain the remote terminal’s address, direction of message transmission, subaddress, and word count.
- Data Words
The bus controller can send 1 to 32 data words when using BC-to-RT transfers or broadcast data messages. For broadcast messages, all remote terminals accept the data, but no terminals respond with Status words.
- Remote and Control Devices
The Bus controller, Remote terminals, and Monitor devices are interconnected over two separate buses. Normal operation involves only the primary bus, with the secondary bus available as a redundant backup if the primary bus fails.
- Message Scheduling
With MIL-STD-1553, most messaging is synchronous; i.e., based on periodic scheduling. In some systems, high-priority aperiodic messages are inserted into gaps between scheduled messages. Whereas, low priority aperiodic messages are inserted at the end of a minor frame.
