CommTech FASTCOM ESCC-PCI-335, Hardware Reference Manual

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15
TERMINATION RESISTANCE
In both the RS-422 and the RS-485 mode, the receiver end of the cable between two stations must be terminated
with a resistor equal to the characteristic impedance of the wire. This is to prevent signal reflections in the wire
and to improve noise rejection. However, you do not need to add a terminator resistor to your cables when
you use the FASTCOM: ESCC-PCI-335. The termination resistance is built in. We have installed a
terminator resistor for each receiver: between each RD+ and RD- and between CTS+ and CTS- for each
channel.
If you are using the FASTCOM: ESCC-PCI-335 in a multi-drop network, the termination resistor should be
removed from all units except the first and last (see the RS-485 illustration below). Call for technical support if
you need to modify the resistor. You may also order the FASTCOM: ESCC-PCI-335 without the termination
resistor installed (it is easier to add the resistor than to remove it). Observe the resistors in the following drawings
and remember that they are built into the FASTCOM: ESCC-PCI-335: