RS485 is a half-duplex bus. In actual use, the host polling or token passing method is generally used to allocate bus control rights. RS485 devices need to change the direction of sending and receiving.The common practice is that each RS485 device is in the receiving state at ordinary times, only when it has data to send, it switches to the sending state, and then switches back to the receiving state again after the data is sent.
What are the common faults of RS485 bus?
In the conventional RS485 bus communication, the RS485 repeater, RS485 converter and other equipment will encounter many problems in the application process, such as: unable to communicate, abnormal data upload and download, communication interference, abnormal flickering of communication indicator light, communication instructions are sometimes on and sometimes off, which affect the normal use. The usual detection methods are as follows:
1. Common ground method: connect the grounding points of all RS485 equipment with one wire or shielded wire to avoid potential difference affecting communication between all equipment.
2. Terminal resistance method: Connect a 120 ohm terminal resistor in parallel on RS485 + and RS485- of the last RS485 device to improve the communication quality.
3. Middle section disconnection method: check whether the equipment is overloaded, the communication distance is too long, and the damage of a certain equipment has an impact on the entire communication line by disconnecting from the middle;
4. Separate wire pulling method: simply and temporarily pull a wire to the equipment to rule out whether the communication failure is caused by wiring.
5. Converter replacement method: Replace several converters to rule out whether the converter quality problem affects the communication quality.
6. Notebook debugging method: First ensure that the notebook computer is a device with normal communication, and then replace it with another computer for communication. If it is possible, it indicates that the serial port of the computer may be damaged or injured.