1. Connection problem: Make sure that the connection between the 485 interface and the device is correct. Check whether the connecting cable is plugged in and the contact is good, and check whether the 485 interface is correctly connected to the communication interface of the equipment.

2. Setup problem: Make sure the communication parameters of the equipment are set correctly. Parameters including baud rate, data bits, parity bits and stop bits shall meet the communication requirements of the equipment. If the settings do not match, the device will not be able to read port 485 correctly.

3. Power supply: 485 communication requires an external power supply. Confirm whether the power supply of the 485 interface works normally and provides enough power for the equipment.

4. Equipment failure: There is no problem in the above steps, but the port 485 is still unreadable, so the equipment itself has failed. At this time, please try to connect the device to another host, or replace it with a new device for troubleshooting. "Plug-in power supply" refers to an operation mode of plug-in power supply. This method is common in some specific devices or scenes, such as smart door locks, chargers, wireless routers and so on.