Standard Rs485 Interface; Figure 2-1 Communication To Front Usb Port; Figure 2-2 Communication To Multiple Devices From Control System Using Rs485 - Siemens 7SR21 Manual

2.1.2

Standard RS485 Interface

The RS485 communication port is located at the rear of the relay and can be connected using a suitable RS485
120 ohm screened twisted pair cable.
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. The relays are fitted with an internal
terminating resistor which can be connected between the A and B by fitting an external wire loop between
terminals 18 and 20 on the power supply module.
The maximum number of relays that can be connected to the bus is 64.
The following settings can be configured via the relay fascia or Reydisp Evolution when using the RS485
interface.
Setting name Range
0 – 254 for IEC60870-5-103
0 – 247 for Modbus RTU
Station Address
0 – 65520 for DNP3.0
OFF, IEC60870-5-103,
COM1-RS485 Protocol
MODBUS-RTU, DNP3.0
75 110 150 300 600 1200
2400 4800 9600 19200
COM1-RS485 Baud Rate
38400
NONE, ODD, EVEN
COM1-RS485 Parity
DISABLED ENABLED
Unsolicited Mode
0 ... 65520
Destination Address
To
Control
System
Rear terminals
Figure 2-2 Communication to Multiple Devices from Control System using RS485
©2010 Siemens Protection Devices Limited
Figure 2-1 Communication to Front USB Port
Default
0
IEC60870-5-
103
19200
EVEN
DISABLED
0
14
16
18
RS485 Screened
twisted pair
7SR21 & 7SR22 Data Communications
Setting Notes
An address within the range of the
relevant protocol must be given to
As Required
identify the relay. Each relay must
have a unique address.
Sets the protocol used to
As Required communicate on the standard
RS485 connection.
The baud rate set on all of the
relays connected to the control
As Required
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
As Required must be the same and in
accordance with the master
device.
Setting is only visible when COM1
As Required
Protocol is set to DNP3
Setting is only visible when COM1
As Required
Protocol is set to DNP3
14 14
16
16
18 18
20
RS485 Screened
Rear terminals
twisted pair
Chapter 4 Page 6 of 15
Ext Wire loop to
Include line
terminating Res