Protocols; Physical Layer; Description - GE Multilin 745 Communications Manual

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Protocols

Physical layer

745 TRANSFORMER PROTECTION SYSTEM – COMMUNICATIONS GUIDE
745 Transformer Protection
System Communications Guide
Chapter 1: Overview
Overview

Description

The GE Multilin 745 Transformer Protection System communicates with other
computerized equipment such as programmable logic controllers, personal computers, or
plant master computers using either the AEG Modicon Modbus protocol or the Harris
Distributed Network Protocol (DNP), Version 3.0. Following are some general notes:
• The 745 relay always act as slave devices meaning that they never initiate
communications; they only listen and respond to requests issued by a master
computer.
• For Modbus, a subset of the Remote Terminal Unit (RTU) format of the protocol is
supported which allows extensive monitoring, programming and control functions
using read and write register commands.
• For DNP, the functionality is restricted to monitoring of essential relay data and control
of important relay functions. A complete description of the services available via DNP
may be found in the Device Profile Document which is included in this chapter.
DNP is a complex protocol. As a consequence, it is not possible within the scope of this
manual to provide a description of the protocol's operation in anything approaching the
detail required to understand how to use it to communicate with the relay. It is strongly
recommended that interested users contact the DNP Users Group at
to obtain further information:
Members of the DNP Users Group are eligible to receive complete descriptions of all
aspects of the protocol. The Users Group also operates a website (http://www.dnp.org)
where technical information and support is available.
Both the Modbus and DNP protocols are hardware-independent so that the physical layer
can be any of a variety of standard hardware configurations including RS232, RS422,
RS485, fiber optics, etc. The 745 includes a front panel RS232 port and two rear terminal
RS485 ports, one of which can also be configured as RS422. Data flow is half duplex in all
configurations. See the 745 instruction manual for details.
http://www.dnp.org
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