bus
bus, refers to the transmission medium shared by all nodes on the network, and is the common path for signal transmission.
Bus segment
bus segment, a group of devices connected together by a bus
Bus protocol
bus protocol, a set of rules for how devices on the bus use the bus
Bus operation
- Connection: The logical binding of communication objects between different devices
- Data transmission: the process of sending and receiving communication messages after the connection is completed, or the process of reading and writing data,
- Disconnect: After completing one or more bus operations, disconnect the connection between the sender and the receiver, and give up the possession of the bus
Field equipment
fieldbus device, as a physical entity connected to the fieldbus as a network node
Bus master
bus master, a device capable of initiating communication on the bus, and has mastered the communication rights of the bus
Bus slave
bus slaver, can't initiate communication on the bus, can only be connected to the bus to receive and query the bus signal
Bus arbitration
bus arbitration
why exist?: A conflict (contention) occurs when more than one device attempts to occupy the bus
Refers to the process of dealing with bus conflicts, according to a certain ruling rule to determine the device with the right to occupy the bus at the next moment.
Access latency: The time a bus device waits for arbitration in order to obtain bus possession.
Bus occupancy period: The time the device occupies the bus.
classification:
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Centralized arbitration
Completed by an arbitration unit, arbitration is carried out using a priority scheme
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Distributed arbitration
The arbitration process is completed in each master device. When they have a bus request, they send their unique arbitration number to the shared arbitration bus, and each arbiter compares the arbitration number obtained from the arbitration bus with its own arbitration number. If the priority of the number on the arbitration bus is high, its bus request will not be responded to, and its arbitration number will be revoked. Finally, the arbitration number of the winner remains on the arbitration bus.