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The RS485 data comms link will be broken for that particular relay element if it is withdrawn from the case but the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