KROHNE UFC 400 Modbus EN - Manual (Page 6)

3
ELECTRICAL CONNECTIONS
6
UFC 400
www.krohne.com 05/2013 - 4002744801 - AD Modbus UFC 400 R01 en
3.1 Modbus connection
The signal converter is hooked up onto the bus using terminals C and D:
Terminals A and B of the signal converter are dependant on the options selected at order. Refer
to the standard handbook of the signal converter for connection details.
3.2 Connection to Modbus bus
The signal converter is designed to be connected as a slave device onto the 2-wire bus
implementation of the Modbus serial physical layer definition.
In addition to the D0 and D1 signal lines the bus MUST MUST MUST MUST include a "Common" signal line to act as a
ground reference point for the data signals.
For proper operation of Modbus in half duplex mode in single or multi-drop communication, it is
recommended that a termination resistor is applied to both ends of the data line. The simplest
form of termination is line-to-line resistor across the differential input.
In RTU mode the Modus protocol requires quiet periods on the communications bus for
synchronisation. It is therefore important that the Modbus is not allowed to "float", i.e.
unreferenced to 0 V, as this could lead to spurious signals due to noise pick-up. It is therefore
necessary to employ biasing resistors at one point on the bus network.
Terminals Description
D- Signal A (D 0)
D Signal B (D 1)
C- Common 0 V
C Not connected