What is the terminal resistance? Terminal resistance is an obstacle encountered in the transmission of electronic information. When high-frequency signals are transmitted, the signal wavelength is shorter than that of the transmission line, and the signal will form reflected waves at the terminal of the transmission line, interfering with the original signal. Therefore, terminal resistance should be added at the end of the transmission line, so that the signal will not reflect after reaching the end of the transmission line. Not for low frequency signals. In the long line signal transmission, in order to avoid the reflection and echo of the signal, it is also necessary to match the resistance in the receiving end access terminal.
The terminal matching resistance depends on the impedance characteristics of the cable and is independent of the length of the cable. Rs-485 /RS-422 generally uses twisted pair (shielded or unshielded) connection with terminal resistance between 100 and 140&Omega, with a typical value of 120&Omega. In actual configuration, connect the two terminal nodes of the cable, namely, the nearest end and the farthest end, to a terminal resistor. The node in the middle part cannot connect to the terminal resistor. Otherwise, communication errors may occur.