P54x/EN SC/La4 SCADA Communications
(SC) 13-4
MiCOM P543, P544, P545 & P546
SC
1.2 Connections to the communications ports
1.2.1 Connections to the front port
The front co
mmunications port is not intended for permanent connection. The front
communications port supports the Courier protocol and is implemented on an EIA(RS)232
connection. A 9-pin connector type, as described in the ‘Getting Started’ chapter of this
manual, is used, and the cabling requirements are detailed in the ‘Installation’ chapter of this
manual.
1.2.2 Connections to the EIA(RS)485 rear port, RP1
The rea
r EIA(RS)485 communication port is provided by a 3-terminal screw connector
located on the back of the relay. See the ‘Installation’ chapter of this manual for details of
the connection terminals. The rear port provides 2-wire EIA(RS)485 serial data
communication and is intended for use with a permanently wired connection. Of the three
terminals on the connection, two are for the signal connection, and the other is for the earth
shield of the cable.
If the IEC 60870-5-103, or the DNP3.0 protocols are specified as the interface for the rear
port, then connections conform entirely to the EIA(RS)485 standards outline below. If,
however, the Courier protocol is specified as the rear port protocol, then the interface can be
set either to EIA(RS)485 or K-Bus. The configuration of the port as either EIA(RS)485 or
K-Bus is described later together with K-Bus details, but as connection to the port is affected
by this choice, the following points should be noted:
Connection to an EIA(RS)485 device is polarity sensitive, whereas K-Bus connection is
not.
Whilst connection to between an EIA(RS)485 port and an EIA(RS)232 port on, say, a PC
might be implemented using a general purpose EIA(RS)485 to EIA(RS)232 converter,
connection between an EIA(RS)232 port and K-Bus requires a KITZ101, KITZ102 or
KITZ201.
Unless the K-Bus option is chosen for the rear port, correct polarity must be observed for the
signal connections. In all other respects (bus wiring, topology, connection, biasing, and
termination) K-Bus can be considered the same as EIA(RS)485.
All rear port communication interfaces are fully isolated and suitable for permanent
connection. EIA(RS)485 (and K-Bus) connections allow up to 32 devices to be ‘daisy-
chained’ together using a simple twisted pair electrical connection.
1.2.2.1 EIA(RS)485 bus
The EIA(RS)485 two
-wire connection provides a half-duplex fully isolated serial connection
to the product. The connection is polarized and whilst the product’s connection diagrams
indicate the polarization of the connection terminals it should be borne in mind that there is
no agreed definition of which terminal is which. If the master is unable to communicate with
the product, and the communication parameters match, then it is possible that the two-wire
connection is reversed.
1.2.2.2 EIA(RS)485 bus termination
The EIA(RS
)485 bus must have 120 Ω (Ohm) ½ Watt terminating resistors fitted at either
end across the signal wires - see Figure 1. Some devices may be able to provide the bus
terminatin
g resistors by different connection or configuration arrangements, in which case
separate external components will not be required. However, this product does not provide
such a facility, so if it is located at the bus terminus then an external termination resistor will
be required.
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