Device Connection; Rs485 Connection - Ebyte M31 Series User Manual

Chengdu Ebyte Electronic Technology Co., Ltd. Distributed IO Host (M31 Series) User Manual

2.2. Device connection

2.2.1. RS485 connection

Note:
When the 485 bus high-frequency signal is transmitted, the signal wavelength is shorter than the transmission line. The signal will form a reflected
wave at the end of the transmission line, interfering with the original signal. Therefore, it is necessary to add a terminal resistor at the end of the transmission line
to prevent the signal from being reflected after it reaches the end of the transmission line. The terminal resistor should be the same as the impedance of the
communication cable, with a typical value of 120 ohms. Its function is to match the bus impedance and improve the anti-interference and reliability of data
communication.
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