1. Overview
The MIL-STD-1553B bus is a differential serial bus used in military and space equipment. It comprises multiple redundant bus connections and communicates at 1Mbps.
The bus has a single active BC and up to 31 RTs. The BC manages all data transfers on the bus using the command and status protocol. The BC 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 5-bit RT address, transmit or receive bit, 5-bit subaddress and 5-bit word count. This allows for up to 32 RTs on the bus. Normally, only 31 RTs can be connected to the bus, since RT address 31（00011111b） is used to indicate a broadcast transfer. A broadcast transfer is one where all RTs accept the following data. Each RT has 30 subaddresses reserved for data transfers. The other two subaddresses (0 and 31) are reserved for mode codes used for bus control functions. Data transfers contain up to 32 data words (16-bit). Mode code command words are used for bus control functions such as synchronization.
2. Word Formats
There are only three types of words in a 1553B message: a command word (CW), a data word(DW), and a status word (SW). Each word consists of a 3-bit sync pattern, 16 bits of data, and aparity bit, making up the 20-bit word. The word formats are given in Figure2.
Message Types
The 1553B bus supports 10 message transfer types, allowing basic point-to-point, broadcast, and BC-to-RT data transfers, mode code messages, and direct RT-to-RT messages. Figure3 shows the message formats.