ITS2.1 User Manual rev.04/1SEP622750P0001 26
7.3 Modbus RTU cabling
A shielded twisted pair cable is required for Modbus, we recommendBelden 3105A. Other cables are acceptable
if they have equivalent specifications.
7.3.1 Terminating resistors (TR)
In order to avoid reflections of the signal, a 120 Ohm terminating resistor must be mounted at both ends of
the main cable. An internal terminating resistance is fitted in the ITS if other devices are connected in addition
to the ITS, it is necessary to verify whether they are equipped or not with terminating resistors (in this case, it
is usually possible to activate or deactivate it). Termination resistors must be used only at both ends of the
main cable.
If the total length of the main cable is less than 50 m, the termination resistors at both ends of the main cable
can be avoided.
7.3.2 Grounding of shielding
The shield of the cable must be connected to ground at a single point (at the master side).
If there is a long distance between the master and the ITS, different potentials may occur, resulting in loss of
communication. To equalize potentials, the 0V line may be used.
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