Doc ID : ADR111A_IM_01
Ref ID : ADR111A/IM/CS
Rev No. : 04
Page No. : 76 of 127
ADR111A /
ADR211A
7 SCADA COMMUNICATIONS
7.1 MODBUS
This section describes how the MODBUS standard is applied to the RT platform. It is not a
description of the standard itself. The level at which this section is written assumes that the
reader is already familiar with the MODBUS standard.
The MODBUS protocol is a master/slave protocol, defined and administered by the
MODBUS Organization. For further information on MODBUS and the protocol specifications
please see the Modbus web site (
www.modbus.org).
Overview: Physical Connection and Link Layer
For connecting on MODBUS use:
Rear serial port - for permanent SCADA connection via RS422/ RS485
The MODBUS interface uses ‘RTU’ mode communication rather than ‘ASCII’ mode as this
provides more efficient use of the communication bandwidth. This mode of communication is
defined by the MODBUS standard.
The IED address and baud rate can be selected using the relay front panel.
When using a serial interface, the data format is: 1 start bit, 8 data bits, 1 stop bit (a total of
10 bits per character).
7.1.1 MODBUS Protocol Map
7.1.1.1 Function Codes supported:
Code Function Name Addresses starts with
02 Read Input Status 1x addresses
03 Read Holding Registers 4x addresses
04 Read Input Registers 3x addresses
05 Force Single Coil 0x addresses
16 Preset Multiple Registers 4x addresses
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