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Delta RMC101 User Manual

Page 497

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Serial (RS-232/422/485) 5.5

Communications

5-247

As described above, hardware revision 1 differs in its biasing and termination. It has the following
differences:

• There is no biasing or termination on the Tx wire pair.

• There is no capacitor in the Rx/Tx termination circuit.

• The values of the resisters in the Rx/Tx biasing circuit are 2.2 kW instead of 1.15 kW.

Termination
Cable termination is a way of absorbing transmitted energy at the end of a network. This prevents
signal reflections from bouncing back towards the transmitter and potentially upsetting signal
quality and communications.

The termination resistor should match the characteristic impedance of the cable being terminated.
The effective impedance of the RMC SERIAL's termination resistor and biasing resistors is 114W.
Therefore, cabling with impedance of 100W to 120W is recommended.

Termination should be placed at the end of the network for each wire pair. The diagrams in Serial
Network Topologies show the correct locations of the termination:

• For RS-422 (4-wire, point-to-point), terminate the receiver of each wire pair.

• For RS-485 (2-wire, point-to-point or multi-drop), terminate the wire pair at each end of the

network.

This manual is related to the following products: