Configuring The Terminating Resistors - Endress+Hauser PROFI BUS Proline Promag 53 PROFIBUS DP Operating Manual

Operation
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#
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84
5.6.3

Configuring the terminating resistors

Note!
It is important to terminate the RS485 line correctly at the start and end of the bus segment since
impedance mismatch results in reflections on the line which can cause faulty communication
transmission.
Warning!
Risk of electric shock. Exposed components carry dangerous voltages.
Make sure that the power supply is switched off before you remove the cover of the electronics
compartment.
• For baud rates up to 1.5 MBaud, the termination is set via the terminating switch SW 1 for the
last transmitter on the bus: ON - ON - ON - ON.
• Device is operated with a baud rate >1.5 MBaud: due to the capacitive load of the user and the
resulting line reflection, make sure that an external termination is used.
In addition, the signal lines have to be protected (= shielded and grounded) for flexible assignment
boards. → Page 61
The miniature switch for termination is located on the I/O board (see Figure):
A
+5V
SW 1
390 W
1
2
220 W
3
4
390 W
OFF ON
Fig. 51: Configuring the terminating resistors (for baud rates < 1.5 MBaud)
A = Factory setting
B = Setting at the last transmitter
Note!
It is generally recommended to use external termination since if a device that is terminated
internally is defect, this can result in the failure of the entire segment.
B
+5V
SW 1
390 W
1
2
220 W
3
4
390 W
OFF ON
1
2
1
2
3 3
4
4
1
2
3
4
3
T
1 P U
2
3 U T
4
T /O
1 P U
2
3 IN
4
4
T
P U
U T
T /O
P U
IN
Proline Promag 53 PROFIBUS DP/PA
1
2
3
4
1
2
3
4
1
2
3
4
Endress+Hauser
a0004392