Endress+Hauser Proline Promag 55 - Configuring the terminating resistors

Operation Proline Promag 55 PROFIBUS DP/PA
68 Endress+Hauser
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 data 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. ä 48.
The miniature switch for termination is located on the I/O board (see Figure):
A0004392
Fig. 48: 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.
1
2
3
4
W
E
N
O
1
2
3
4
W
E
N
O
1
2
3
4
W
E
N
O
INPUT/OUTPUT
4
INPUT/OUTPUT
3
1
2
3
4
W
E
N
O
1
2
3
4
W
E
N
O
1
2
3
4
W
E
N
O
1
2
3
4
W
E
N
O
1
2
3
4
W
E
N
O
390 W
+5V
A
3
4
1
2
OFF ON
220W
390 W
SW1
390 W
+5V
B
3
4
1
2
OFF ON
220W
390 W
SW1