KROHNE GFC 300 Modbus - Manual (Page 5)

CONNECTION IN BUS SYSTEMS
3
5
GFC 300
www.krohne.com 03/2012 - 7312402100 - AD Modbus GFC 300 R01 en
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, normally the "end".
The Modbus converter has two conditions. Default is without termination and polarization. To get
the active termination and polarization the settings of jumper X5 and X6 on Modbus board must
be changed. This can only be done by qualified personnel. For detailed information, refer to
Electrical connection on page 7.