The MIL-STD-1553B bus is a differential serial bus used in military and space equipment. It is comprised of multiple redundant bus connections and communicates at 1MB per second.
The bus has a single active bus controller (BC) and up to 31remote terminals (RTs). The BC manages all data transfers on the bus using the command and status protocol. The bus controller initiates every transfer by sending a command word and data if required. The selected RT will respond with a status word and data if required.
The 1553B command word contains a five-bit RT address, transmit or receive bit, five-bit sub-address and five-bit word count. This allows for 32 RTs on the bus. However, only 31RTs may be connected, since the RT address (31) is used to indicate a broadcast transfer, i.e. all RTs should accept the following data. Each RT has 30 sub-addresses reserved for data transfers. The other two sub-addresses (0 and 31) are reserved for mode codes used for bus control functions. Data transfers contain up to (32) 16-bit data words. Mode code command words are used for bus control functions such as synchronization.