Control Techniques UD70 User Manual page 63

Terminating the cable
When a multi-drop
the two receive lines of the last unit in the chain (ie. the unit farthest away
from the host). Care must be taken to ensure that other units in the system
do not have the resistor already fitted. Excessive signal loss will occur if
termination resistors are connected to units other than the last one.
Connections for 4-wire mode Connections for 4-wire mode
Connections for 2-wire mode Connections for 2-wire mode
UD70
Issue code: 70nu2
system is used, connect a 120Ω resistor between
RS485
Serial communications 6-3