iSMA-B-FCU Hardware User Manual
www.ismacontrolli.com
DMP242en | 1st Issue rev. 3 | 02/2022
page 13 of 53
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4.4.2 RS485 Grounding and Shielding
In most cases controllers are installed in enclosures along with other devices, which
generate electromagnetic radiation (for example, relays, contactors, transformers, motor
invertors, etc.). Such electromagnetic radiation can induce electrical noise into both
power and signal lines, as well as direct radiation into the controller, causing negative
effects on the system. For this reason, an appropriate grounding, shielding, and other
protective steps should be taken at the installation stage to prevent negative
electromagnetic radiation effects, for example:
control cabinet grounding;
cable shield grounding;
using protective elements for electromagnetic switching devices;
proper wiring;
consideration of cable types and their cross sections;
and other.
4.4.3 RS485 Netowrk Termination
Transmission line effects often present problems for data communication networks.
These problems include reflections and signal attenuation.
To eliminate the presence of reflections of signal from the end of the cable, the cable
must be terminated at both ends with a resistor across the line adequate to its
characteristic impedance. Both ends must be terminated since the propagation is
bidirectional. In case of an RS485 twisted pair cable this termination is typically 120
Ω.
4.5 RJ12 Panel Connection
The RJ12 socket is designed for connecting external modules and LCD panel. The iSMA-B-
FCU device has two parallel sockets with the same pin configuration. These sockets
provide communication in the Modbus RTU protocol.
The RJ12 socket provides also power supply dedicated for external LCD panels with
maximum load up to 2.5 W. Before connecting devices powered from RJ12, please
calculate the power supply load. Power consumption of the dedicated wall panels iSMA-
B-LP with temperature sensor is 0.5 W, so the maximum number of panels on the bus is
5. The maximum number of Touch Point panels on the bus is also 5.
RJ12 pins are shown in the figure below.
