Wiring failure and debugging method of 485 bus structure of access control system

No communication, no response.

Data can be uploaded, but data cannot be downloaded.

During communication, the system prompts interference. Or when there is no communication, the communication indicator flashes continuously.

Sometimes communication is possible, sometimes communication is not possible. Some commands can be communicated, and some commands cannot.

Recommend several debugging methods:

First, make sure that the equipment wiring is correct and strictly in accordance with the specifications:

1. Common ground method: Connect the GND ground of all 485 devices with 1 wire or shielded wire, so as to avoid the potential difference that affects communication between all devices.

2. Terminal resistance method: Connect 120 ohm terminal resistance to the 485+ and 485- of the last 485 device to improve the communication quality.

3. Intermediate segment disconnection method: By disconnecting from the middle to check whether the equipment is overloaded, the communication distance is too long, the influence of a certain equipment damage on the entire communication line, etc.

4. Separate cable pull method: Simply pull a cable to the device temporarily, which can be used to eliminate whether the wiring caused the communication failure.

5. Replace the converter method: Carry several converters with you, so you can rule out whether the quality of the converter affects the communication quality.

6. Notebook debugging method: First ensure that the computer notebook you carry with you is a device with normal communication. Replace the customer's computer for communication. If you can, it indicates that the serial port of the customer's computer may be damaged or injured.