485 Point-to-Many Communication Problem

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485 Point-to-Many Communication Problem [Copy link]

 

485 point-to-multiple communication, using modbus communication protocol, daisy-type connection, FPGA sends data, and two devices are mounted to receive data (address 01 and 02). It is sent in serial mode (and in time sequence, send a frame of data, delay for a period of time), and there is no problem with the receiving device. Now it needs to be improved. Continuously send data to a device 02, insert a frame of data during the idle time of sending data, and during the delay time (the delay time is longer than the time required to send a frame of data). The problem is that after inserting this frame of data, the data of device 02 has problems at the place where the data frame is inserted, and the data of device 02 does not change according to the rules. What is the reason for this? It is hoped that the data of device 02 will not be affected, and the data communication of device 01 is normal. The figure below is the waveform diagram of FPGA simulation and device 02.

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As long as data appears on the bus, all nodes will receive it. To prevent a node from being affected by the inserted data, it should close the serial port reception after receiving all the data sent to itself, and then open it again after the delay time is reached. However, such operation is not standardized, at least the protocol is no longer universal. A better way to deal with it is to strictly implement the protocol. Data not from this node should not be responded to at all, and naturally there will be no data problems. It can be seen that there is a problem with your protocol parsing program.