Siemens 7SR18 Solkor Manual page 228

The RS485 electrical connection can be used in a single or multi-drop configuration. The RS485 master must support
and use the Auto Device Enable (ADE) feature. The last device in the connection must be terminated correctly in
accordance with the master device driving the connection. This can be done via the internal 120 ohm terminating
resistor, which can be connected between 14 (A) and 18 (B) by fitting an external wire loop between terminals 18
and 20 on the power supply module.
The polarity of the signal terminals is marked as A and B in line with the RS485 standard. The polarity is that when
the bus is in the quiescent state and no communication is taking place, the B terminal is more positive than A. This
can be used to identify the polarity of any equipment to be connected, typically measured at each terminal in turn
to ground. Connection of the device to a termination network at the end of the bus will also be to suit the quiescent
state as shown in the diagram below.
The polarity marking is often found to be reversed or marked as +/- on other equipment so care is required. If the
devices are connected in reverse, communication to all devices will be disturbed but no damage will occur. If problems
are experienced during commissioning, the connections should be tried in reverse.
The maximum number of relays that can be connected to the bus is 64.
The RS485 data comms link will be broken for that particular relay element if it is withdrawn from the case but the
chain of communication to the other relays is maintained.
The following settings, on the COMMUNICATIONS MENU, must be configured when using the RS485 interface.
Setting Name
OFF
COM1-RS485 IEC60870-5-103
Protocol MODBUS-RTU
DNP3
COM1-RS485 0 - 254 for IEC60870-5-103
Station 1 - 247 for Modbus RTU
Address 0 - 65534 for DNP3.0
75 110 150 300
COM1-RS485
600 1200 2400 4800
Baud Rate
9600 19200 38400
NONE
COM1-RS485
ODD
Parity
EVEN
Local
COM1-RS485
Local or Remote
Mode
Remote
© 2016 Siemens Protection Devices Limited
Chapter 4 - 7SR181 Solkor · Data Communications Definitions
Range/Options Default Setting
IEC60870-5-103
0
19200
EVEN
Remote
Notes
The protocol used
to communicate on
the standard RS485
connection.
An address within the
range of the relevant
protocol must be
given to identify the
relay. Each relay in a
network must have a
unique address.
The baud rate set
on all of the relays
connected to the
control system must
be the same as the
one set on the master
device.
The parity set on
all of the relays
connected to the
control system must
be the same and in
accordance with the
master device.
Refer to Appendix
1, page 79, for
further explanation
Chapter 4 - Page 9 of 80