Lindy RS-422/485 user manual Jumper Settings

6.1 Jumper Settings

These cards feature built-in termination resistors for each serial port. You can modify the jumper settings (short the pins) to avoid impedance mismatch problems when operating under multi-drop transmission.

When an electrical signal travels through two resistance junctions in a transmission line, the impedance mismatch will sometimes cause signal reflection. Signal reflection causes signal distortion, which in turn contributes to communication errors. The solution to this problem is to establish the same impedance at the line ends as in the line itself by terminating them with resistors. It is normally sufficient when the value of the termination resistors equals the characteristic impedance of the transmission line. LINDY RS-422/485 serial boards feature built-in termination resistors to prevent these problems.

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