Data communication method of redundant CAN bus communication system

Abstract

A data communication method of a redundant CAN bus communication system comprises the following steps: a sending terminal sends PDO messages containing a scrolling count value a on two CAN buses; when the sending terminal sends the PDO messages with the same message ID, each time a frame of the PDO message is sent, the scrolling count value a is increased by 1, the initial value of a is 0, the upper limit value of a is N, and when a reaches N, the count is restarted from 1; an expectation counter and an invalid receiving window are arranged at a receiving terminal, and the count value b of the expectation counter indicates the scrolling count value of the PDO message that is expected to be received; when receiving a frame of the PDO message sent by the sending terminal each time, the receiving terminal firstly judges whether the message is valid; if the message is valid, and a is equal to 0, b is set to 1; if the message is valid, and b is less than N, b is updated to b=a+1, and if b is equal to N, b is set to 1; and when the receiving terminal receives the invalid messages, the invalid messages are discarded, and b is maintained to be unchanged. According to the data communication method disclosed by the invention, the shock of the old and new data generated by the receiving terminal can be avoided.

Description

technical field [0001] The invention relates to field bus communication technology, in particular to a data communication method of a redundant CAN bus communication system. Background technique [0002] At present, CAN bus technology has been widely used in the field of industrial control. CAN bus is divided into physical layer, data link layer and application layer. Among them, the physical layer and the data link layer follow the CAN2.0 protocol specification. In 1992, the CIA organization was established, and one of its first tasks was to develop the CAN application layer protocol. Currently, the adopted protocol specifications include DeviceNet, CANOpen, etc. The CANOpen specification is an authoritative specification in the field of industrial control, which includes a series of documents. Among them, the most basic one is CANOpen301, which has been officially released and applied. In addition, CANOpen302 is a specification for floating master nodes, and CANOpen30...

AI Technical Summary

Problems solved by technology

However, it has the following problems: (1) data loss and delayed transmission of data may occur during bus switching; (2) when the CAN bus used has a short-term interference or fault, the mechanism loses redundancy. Therefore, for real-time systems, cold standby systems are not suitable

However, this communication method has the following problems: (1) The setting of the time window cannot be infinitely large, and must be smaller than the prohibition time of the message, otherwise there will still be a problem of out-of-order; (2) In the limited time window, there may be The following situation occurs: when both CAN buses receive interference, it will cause a delay in the sending of bus messages, and the messages on both CAN buses exceed the set time window, and the messages will be discarded

Then, for real-time embedded systems, discarding important messages and delaying the receiving time of messages will have unpredictable and even destructive effects on the system

(3) Complicated in code implementation mechanism

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