Xeo4 RILHEVA II, User Manual, Page: 31 / 35

31
Grounding
Be sure that all the devices will use the same ground, especially if using more than one power supply. The
RS485 line shield should be grounded only to a single line end.
RS-485 bus polarization
For the RS-485 bus to be working correctly, it is necessary that electric signals are polarized in a proper
way.
When all the Modbus slave devices are listening and the master device (namely Rilheva) is not polling
(transmitting), the RS-485 bus will remain in high-impedance status.
In this situation, sometime, the RS-485 bus may be interfered by some external electromagnetic noise that
could be interpreted as real signals by the listening stations.
You can check whether the RS-485 bus is polarized properly by using a common tester (digital multimeter)
and measuring the voltage between the ter and – (while no traffic exists on the bus) and verifying
that the voltage is greater than 200 mV.
If not, you should connect two polarization resistors:
•
one between te (B) and terminal VEXT (+)
•
one between terminal – (A) and terminal VEXT (C)