Common methods of maintaining RS485
1) If the system is completely paralyzed, it is mostly because the VA and VB of a certain node chip break down to the power supply. Use a multimeter to measure the differential mode voltage between VA and VB to zero, and the common mode voltage to ground is greater than 3V. Check the common-mode voltage, the larger the common-mode voltage, the closer to the fault point, and vice versa;
2) Several consecutive nodes on the bus cannot work normally. Usually caused by the failure of one of the nodes. A node failure will cause the adjacent 2 to 3 nodes (usually the follow-up) to be unable to communicate, so they are disconnected from the bus one by one. If the bus returns to normal after a node is disconnected, it means that the node is faulty;
3) When the RS-485 system with centralized power supply is powered on, some nodes are often abnormal, but it is not exactly the same every time. This is due to the unreasonable design of the RS-485 transceiver control terminal TC, which causes the node transceiver state to be chaotic when the microsystem is powered on, resulting in bus blockage. The improved method is to add a power switch to each microsystem and then power on it separately;
4) The system is basically normal but communication failures occasionally occur. Generally, the reliability of the system is in a critical state due to unreasonable network construction. It is best to change the wiring or increase the relay module. One of the emergency methods is to replace the failed node with a chip with better performance;
5) The TC terminal is in a long hair state due to MCU failure, and the bus is pulled to death. Remind readers not to forget to check the TC side. Although RS-485 stipulates that the differential mode voltage is greater than 200mV, it can work normally. But the actual measurement: the differential mode voltage of a well-running system is generally around 1.2V (due to the difference in network distribution and speed, the differential mode voltage may be in the range of 0.8~1.5V).
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