Date Code 20010719
701 Motor Protection Relay
Appendix C
Modbus
®
RTU
Communications Protocol
Introduction
This appendix describes Modbus
â
RTU communications features supported by
the SEL-701 Relay at the rear-panel EIA-485 port. Complete specifications for the
Modbus protocol are available from Modicon on their web site: www.modicon.com.
The SEL-701 Relay supports Modbus RTU protocol when you enable Modbus
protocol using the rear-panel serial port settings. When Modbus protocol is enabled,
the relay activates the rear-panel EIA-485 serial port and deactivates the EIA-232
serial port.
Modbus RTU is a binary protocol that permits communication between a single
master device and multiple slave devices. The communication is half-duplex: only one
device transmits at a time. The master transmits a binary command that includes the
address of the desired slave device. All of the slave devices receive the message, but
only the slave device having the matching address responds.
The SEL-701 Relay Modbus communication allows a Modbus master device to:
Acquire metering, monitoring, and event data from the relay.
Control SEL-701 Relay output contacts and selected internal logic
variables.
Read the SEL-701 Relay self-test status and learn the present
condition of all the relay protection elements.
Содержание SEL-701
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