The composition of the second word in the 1553B protocol

1553B Introduction
This document designs an abstraction layer for the 1553B Device Driver Under sylixos to further remove the coupling between the user layer and the driver layer.
MIL-STD-1553B bus is a standard bus of the United States Air Force electronic subsystem network, is a centralized Serial Bus, bus consists of a bus controller, responsible for bus scheduling, management, it is the initiator and organizer of bus communication. Several (up to 31) remote terminals can also be used to monitor the operation of bus. The bus uses the command response method to implement system communication, and uses redundant channels, odd checks, and corresponding error handling to improve the reliability of system communication. 1553B is the standard for bus interface rules and signal characteristics. It strictly specifies the electrical signal characteristics produced by hardware components on the physical layer, at the data link layer and network layer, the error monitoring methods and command response formats are also strictly defined. The 1553B bus has high reliability and is widely used in electronic networking systems in aviation, aerospace, military, and other fields.
1553B bus adopts asynchronous data transmission mode and the code speed is 1 Mbps (now a 4 Mbps card is available), that is, 106 bits per second. The data encoding adopts the Manchester II code and differential transmission, shield twisted pair wires are generally used as transmission media.
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1553B Software Structure
2.1 message composition
The 1553B protocol specifies that the minimum unit of a message is a word. Each message transmitted on the 1553B bus is composed of individual words.
2.2 characters
It is an information series. The 1553B protocol requires that each word is composed of 20 consecutive bits, including the synchronization header, 16-bit information segment, and a parity bit. As shown in 2.1, these words are divided into three categories: script words, data words, and status words. The following sections describe these words one by one.

Figure 2.1 15533b
2.3 commands/command words

Figure 2.2 command/command Word Format
2.2 The instructions should be set by the synchronization header, remote terminal address field, and sending/receiving bit (T/R), sub-address/Mode Field, data word count/mode code field, and parity bit (P. The script is issued by the BC end, and the corresponding RT port receives the script to perform the operations required by the script to implement data interaction.
2.3.1 synchronization Header
The data synchronization header should be an invalid Manchester waveform. When its width is three digits, the waveform of the first 1.5 digits is negative, and the waveform of the last 1.5 digits is positive. If the front and back bits of the synchronization header are logical 1, the apparent width of the synchronization header is increased to four bits.
2.3.2 remote terminal address segment
The five digits following the synchronization header should be the remote terminal address segment. Each remote terminal is specified as a private address, from the decimal address 0 to the decimal address 30 can be used, but do not use the decimal address 0 as the private address of the remote terminal. The decimal address 31 (11111) is also the public address of all remote terminals for the system to use for broadcast operations.
2.3.3 send and receive bits
The one next to the remote terminal address should be the sending/receiving bit. It shall indicate the operations required by the remote terminal. Logic 0 specifies the remote terminal for receiving operations, and logic 1 specifies the remote terminal for sending operations.
2.3.4 subaddress/Method Field
The five digits following the sending/receiving bits are used to distinguish the sub-addresses of the remote terminal, or to mark (00000 and 11111) when the bus system controls the mode ). If this field is 00000 or 11111, it indicates that the command is a mode control command. If this field is not 00000 or 11111, it indicates the Child address of the RT terminal. Therefore, BC can determine the mode of the script by configuring the sub-segment, can access the data corresponding to the RT0x01-0x1E subaddress.
2.3.5 data word count/method code field
The five digits following the Sub-address/mode field are used to specify the number of data words that should be sent or received by the remote terminal, or the code that can be configured in any way. A maximum of 32 data words can be sent or received in any message block. Full 1 indicates 31 in decimal notation, and full 0 indicates 32 in decimal notation. Therefore, if the 9-14 characters in the script are RT subaddresses, this segment indicates the number of sent or received messages. Otherwise, it indicates the method code. The related method code has been specified in the 1553B protocol and will be detailed later.
2.3.6 parity bit
The last application of the word is used as the first 16-bit parity. 1553B uses the odd check method to ensure data accuracy.
2.4 data words

Figure 2.3 Data Word Format
The data word 2.3 is composed of three synchronization fields, a 16-bit data field, and a one-bit parity bit. The data word is sent from one end of BC or RT to realize data interaction between two terminals.
2.4.1 synchronization Field
The data synchronization header should be an invalid Manchester waveform. When its width is three digits, the waveform of the first 1.5 digits is negative, and the waveform of the last 1.5 digits is positive. If the front and back bits of the synchronization header are logical 1, the apparent width of the synchronization header is increased to four bits.
2.4.2 data fields
The last 16 bits of the synchronization header are data storage bits. You can fill these 16 bits for data transmission.
2.4.3 parity check bit
The last application of the word is used as the first 16-bit parity. 1553B uses the odd check method to ensure data accuracy.
2.5 status characters

Figure 2.4 status Word Format
The status word shown in 2.4 consists of three synchronization segments, five remote terminal address segments, one message error bit, one testing method bit, one service request bit, 3-bit standby segment, 1-bit broadcast command receiving bit, 1-bit busy bit, 1-bit subsystem sign bit, 1-bit dynamic bus control receiving bit, 1-bit Terminal the flag and the one-bit parity bit. The status word is the word sent by the RT end to the BC end to indicate the message and the RT's own status. It is also used as the RT response word to determine whether the 1553B bus or RT device works normally.
2.5.1 synchronization Header
The data synchronization header should be an invalid Manchester waveform. When its width is three digits, the waveform of the first 1.5 digits is negative, and the waveform of the last 1.5 digits is positive. If the front and back bits of the synchronization header are logical 1, the apparent width of the synchronization header is increased to four bits.
2.5.2 remote terminal address field
The five digits following the synchronization header should be the remote terminal address segment. Each remote terminal is specified as a private address, from the decimal address 0 to the decimal address 30, but do not use the decimal address 0 as the private address of the remote terminal.
2.5.3 message error bit
The 9th-bit Status field indicates that one or more words in the received message of the Remote Terminal fail the specified validity test. Logic 1 indicates that the message has an error, and logic 0 indicates that the message has no error. All terminals should provide message difference misplacement.
2.5.4 test location
The 10th bits of the status word are used as the test device bit. It is always set to logic 0 under all conditions. This is an optional bit. If used, the corresponding position in the script is logical 1, which is used to distinguish between the script and the status word.
2.5.5 service request bit
The 11th position of the status word is the service request bit. Indicates that the remote terminal needs services. The bus controller is required to start the scheduled operation related to the remote terminal or subsystem. When multiple subsystems connected to a single remote terminal request services separately, the remote terminal should convert their respective service request signal logic "or" into a single service request in the status word. After the logic "or" is completed, the designer must prepare a data word and mark the specific request service subsystem with the corresponding location 1. The "service request bit" in the "status" should be maintained until several request signals are processed. This bit is only used to stimulate random data transmission operations.
2.5.6 standby status bit
The 12th, 13, and 14 bits of the status word are the standby status bits. They should be set to logic 0, which will be reserved for future use.
2.5.7 broadcast instruction receiving bit
The 15th position of the Status bit is logical 1, indicating that the previous valid script received by the remote terminal is a broadcast script. When the broadcast mode is not used in the system, set this bit to logic 0.
2.5.8 busy bit
The 16th-bit time slot of the status word is logical 1, indicating that the remote terminal is busy, indicating that it cannot move data into the subsystem or retrieve data from the subsystem according to the instructions of the bus controller. If the remote terminal is set to a busy location in response to sending and instruction, only the status word is sent. This is an optional bit. Logical 0 indicates idle or not busy.
2.5.9 subsystem flag
The 17th-bit status code is used to indicate the subsystem fault status to the bus controller and warn the bus controller that the data provided by this remote terminal may be invalid. If several subsystems connected to a remote terminal are in a fault state, the respective signal logic "or" should be used to form the subsystem flag in the state word, the corresponding position 1 in a prepared data word is recorded for further detection and analysis. This is an optional bit. Logic 1 indicates a flag, and logic 0 indicates no flag.
2.5.10 dynamic bus control receiver
If the 18th-bit status is set to logic 1, it indicates that the remote terminal accepts the authorization of dynamic bus control complying with the Protocol itself. Logic 0 indicates no. This is an optional bit.
2.5.11 terminal flag
The 19th-bit status word is reserved as a terminal flag. Logic 1 indicates that a fault exists in the remote terminal and the bus controller is requested to intervene. Logic 0 indicates that no fault exists. This is an optional bit.
2.5.12 parity bit
The last character is used for the first 16-bit parity. 1553B uses the odd check method to ensure data accuracy.

The composition of the second word in the 1553B protocol