Information
The internal terminations of the repeaters are not activated in the factory setting. Those of the display
and operating devices are activated in the factory setting. If a resistance is activated at the input or
output, it is 150
Ω
(the data in the operating instructions must always be observed!)
The PC card (RS232/RS485 gateway), EC-Controller, adapter and accessory modules have no
integrated terminating resistances. Chapter 3.2 describes in brief where the terminating resistances
are best positioned.
4.4
Bias of the line
All the devices on the bus are in reception mode in the quiescent state of the RS-485 bus. If a
termination is used and the bus has no driving variable, the bus line is in an unde
fi
ned state. Bias
resistors (failsafe) must be used to then obtain a de
fi
ned voltage potential on the data lines in the
quiescent state. The bias resistors act for data line "A" (D+) as pull-up resistors (normally against 5 V)
and for data line "B" (D-) as pull-down resistors (against GND).
The following devices usually have built-in bias resistors:
•
MODBUS-master
•
MB/TCP Gateway
•
Repeater
For single devices these must be activated via jumper.
Information
Please see the "RS-485 interface for MODBUS - RTU" section of the individual device instructions!
5 V
Common
(GND)
1
1
2
Picture 8: Example for built-in resistors
1
Bias resistor
2
Line termination
4.5
Pin assignment
Different Ziehl-Abegg designation
D+ corresponds to the connection (A)
D- corresponds to the connection (B)
Technical information
MODBUS RTU System
–
model series
Physical MODBUS transmission layer
R-TIL08_01-GB 1215
Part.-No.
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