MIL-STD is a military standard published by the United States Department of Defense that defines the mechanical , electrical , and functional characteristics of a serial data bus. It was originally designed as an avionic data bus for use with military avionics , but has also become commonly used in spacecraft on-board data handling OBDH subsystems, both military and civil. Air Force standard in , and first was used on the F Falcon fighter aircraft. It is now widely used by all branches of the U.
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General Sales ueidaq. Visit this page for local offices and distributors. MIL-STD is a military standard that defines mechanical, electrical, and operating characteristics of a serial data communication bus for the U.
Department of Defense. It is now commonly used for both military and civilian applications in avionics, aircraft, and spacecraft data handling.
It was first used in the F fighter aircraft and is now widely used by all branches of the U. The current standard, MIL-STDB was introduced in , the goal of which was to define explicitly how each option should function, so that compatibility among manufacturers could be guaranteed. The first and most obvious difference is that most links are designed with dual, redundant channels.
Not all interfaces support all three functions. Be sure the interface you select has the capability you require. As with the ARINC bus, when operating as a bus controller, the unit must be capable of detailed transmission scheduling including major and minor frame timing and this is best per- formed in hardware rather than via software timing.
A single bus consists of a shielded twisted-wire pair with 70 - 85 ohm impedance at 1 MHz. If a coaxial connector is used, the center pin is used for the high Manchester bi-phase signal. All transmitter and receiver devices connect to the bus either through coupling transformers or directly through stub connectors and isolation transformers, as shown below.
Stubs can be a maximum of 1 foot in length for direct coupling or a maximum of 20 feet for transformer coupling. The below image shows one of the two buses. Each transceiver is also connected in the same way to the second redundant bus.
Our IO board has 2 channels. All messages on the bus contain one or more bit words, classified as command, data, or status word types. Each word is preceded by a 3 ms sync pulse and is followed by an odd parity bit. Note that since the sync pulse — 1. The words in a message are transmitted with no gap between words, but a 4 ms gap is inserted between successive messages.
All devices must start transmitting a response to a command within 4 to 12 ms. If they do not start transmitting within 14 ms, they are considered to have not received the command message. Each word type has a specific format within a common structure.
All words are 20 bits in length and the first three bits are a synchronization field, which enables the decoding clock to re-sync at the beginning of each new word. The next 16 bits contain the information, in a format that varies with the word type. The last bit in the word is a parity bit, which is based on odd parity for a single word. All bit encoding is based on bi-phase Manchester II format, which provides a self-clocking waveform. The signal is symmetrical about zero and is therefore compatible with transformer coupling.
In Manchester coding, signal transitions occur only at the center of a bit time. Note that the voltage levels on the bus are not the information signal; all information is contained in the timing and direction of the zero crossings of the signal on the bus. The terminal hardware provides the encoding and decoding of the various word types.
The encoder also calculates parity. For received messages, the decoder signals the logic what sync type a word is and whether or not parity is valid. For transmitted messages, input to the encoder defines what sync type to place at the beginning of a word. The encoder calculates parity automatically for each word. A Command Word format uses the first 5 bits for the address of the Remote Terminal 0 to The sixth bit is 0 for Receive and 1 for Transmit.
All other bits direct the data to specific functions in the subsystem. The next 5 bits define the Word Count or Mode Code to be performed. If this field is B or B, the field defines a mode code to be performed. A word count field of B means 32 data words. A data word contains the information being transferred in a message. The first 3 bit times contain a data sync, which is opposite to that used for a command or status word. Data words can be transmitted by either a remote terminal transmit command or a bus controller receive command.
The remote terminal is the reference point. The next 16 bits may be used however the designer wishes. The only standard requirement is that the most significant bit must be transmitted first. A remote terminal responds to a valid message by transmitting a status word. The status word tells the bus controller whether or not a message was received properly and what the state of the terminal is.
The status word is cleared after receiving a a valid command word. After the status word is cleared, the bits are set again if the conditions that set the bits initially still exist.
If an error is detected in the data, the Message Error bit is set and transmission of the status word is suppressed. Transmission of the status word is also suppressed whenever a broadcast message is received. The first 5 bits of the status word bits are the Terminal Address. The remote terminal sets these bits to the address to which it has been programmed. The bus controller examines these bits to ensure that the responding terminal is the one to which the command word was addressed.
The next bit 9 is the Message Error bit, which is set by the terminal on detection of an error or an invalid message. Whenever this bit is set, none of the data received in the message is used. When an error is detected, the remote terminal must suppress transmission of the status word. The Instrumentation bit 10 differentiates a command word form a status word both have the same sync pattern. Since this bit is the most significant bit of the subaddress field, using it as an instrumentation bit reduces the number of available subaddresses from 30 to Because of this limitation, most systems today use techniques other than the instrumentation bit to differentiate between command and status words.
The Service Request bit 11 enables a terminal to inform the bus controller that it needs to be serviced. It is typically used when the bus controller is polling the terminals. This bit is typically not used in modern system designs and is discouraged by Notice 2 of the standard. After setting this bit, the remote terminal becomes the bus controller.
A Remote Terminal can be used as an interface between the bus es and a subsystem or as a connector between this bus and another bus. A subsystem is the sender or user of the information transferred on the bus. A remote terminal contains all the components needed to transfer the data from the sender source to the destination user.
The Bus Controller BC manages the flow of data on the buses. Only one bus controller can be active at a given time. A Word controller, which handles one word at a time, is seldom used today because of the processing burden it places on the subsystem. A Message Controller handles one message at a time, interacting with the computer only when a message is complete or when a fault occurs.
A Frame Controller can process multiple message in a defined sequence, interrupting the computer only when the message stream is complete or after an error is detected. A Bus Monitor is not able to transmit messages on the bus; its function is to monitor, and record, messages being transmitted on the bus without disrupting other devices. A bus monitor can be set up to record selected subsets of the messages on the bus. It can also be set up as a backup bus controller, ready to take over whenever needed.
Each IO board has 2 channels. Each channel is a complete system with Side A and Side B. This video shows you how easy it is to set up and use.
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Research and Design of 1553B Protocol Bus Control Unit
In avionics system, the B interface board is an important part in the whole system, and it mainly integrates data in bus, share resources, coordination tasks, and fault-tolerant reconstruction. The technology of compatible with high-performance general-purpose microcomputer and large-scale integrated circuits is widely applied to complete interface communication from the 80s in our country. The Bus Controller Unit BCU not only insures sending or receiving commands is correct, but also monitors the bus status. The chapter introduces a new design method based on B protocol in order to design BCU. Based on in-depth study, B bus transport protocols and foreign design method of chip, and combined with popular EDA technology, the chapter has designed successfully the digital B MIL-STD-BCU under the top-down design method, and proved to be correct on self-designed experiment board. Skip to main content.