Rs485 Interface - Siemens 7SR224 Technical Manual

2.1.4

RS485 Interface

An RS485 communication port is located on 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. 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 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The RS485 data comms link will be broken for that particular relay element if it is withdrawn from the case but the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.
An additional RS485 port is available as an ordering option. This port is wired to a dedicated terminal block at the
relay rear.
The following settings must be configured via the relay fascia or Reydisp when using the RS485 interface. The
shaded settings are only visible when DNP3.0 is selected.
Setting name Range
1 – 254 for IEC60870-5-
103 or IEC60870-5-101
Station Address
0 – 247 for Modbus RTU
0 – 65534 for DNP3.0
OFF, IEC60870-5-103,
MODBUS-RTU, DNP3.0
COM1-RS485 Protocol
or IEC60870-5-101
75 110 150 300 600 1200
COM1-RS485 Baud
2400 4800 9600 19200
Rate
38400
NONE, ODD, EVEN
COM1-RS485 Parity
Local, Remote, Local Or
COM1 Mode
Remote
Rear terminals
To Control
System
14
16
18
To Control
System
RS485
Figure 2-2 Communication to Multiple Devices from Control System using RS485
©2010 Siemens Protection Devices Limited
Default
1
0
0
IEC60870-5-
103
19200
EVEN
Remote
RS485 Screened
twisted pair
14
16
18
RS485
7SR224 Argus Data Comms
Setting Notes
An address within the range
of the relevant protocol must
As Required
be given to identify the relay.
Each relay must have a
unique address.
Sets the protocol used to
As Required communicate on the RS485
connection.
The baud rate set on all of
the relays connected to the
As Required same RS485 bus must be
the same as the one set on
the master device.
The parity set on all of the
relays connected to the
As Required same RS485 bus must be
the same and in accordance
with the master device.
Remote Selects port mode
Rear terminals
RS485 Screened
twisted pair
RS 485 Twisted pair Cable
RS485
Chapter 4 Page 7 of 76
Ext Wire loop
(terminating
resistance) added
where permanent
drive from master
14 station available
16
18
20