The Rs485 Bus Biasing; Using Fieldbus Through An Rs485 Cable - Danfoss VACON 100 INDUSTRIAL Operating Manual

Operating Guide | VACON® 100 Wall-mounted Drives
A
A Cable clamp
C Cable gland
Illustration 38: Grounding the Cable Shield

7.4.5.3 The RS485 Bus Biasing

When no device on the RS485 bus line transmits data, all devices are in an idle state. In such conditions, the bus voltage is in an
indefinite state, usually near 0 V, because of the termination resistors. This can cause problems in character reception because the
RS485 standard considers the voltage interval from -200 m to +200 mV as an undefined state. Thus, bus biasing is necessary to keep
the voltage in state '1' (above +200 mV) also between the messages.
Unless the first and last device in the RS485 bus line have a built-in bus biasing function, you must add a separate active termination
resistor specially designed for the RS485 bus (e.g. Siemens active RS485 terminating element 6ES7972-0DA00-0AA0).

7.4.5.4 Using Fieldbus through an RS485 Cable

Prerequisites:
Open the covers according to instructions in
Terminals for MR8, or 6.4.3 Get Access and Locate the Terminals for
80 | Danfoss A/S © 2019.05
B C
6.4.1 Get Access and Locate the Terminals for
B Ground terminal
MR4-MR7,
MR9.
Control Unit
6.4.2 Get Access and Locate the
AQ298036140958en-000101 / DPD01711