1MDU07205-YN rev. F
REF601 CEI
User’s manual
74
Serial Communication
Section 7 Serial communication
7.1 Modbus Protocol Overview
The Modbus protocol was fi rst introduced by Modicon Inc. The protocol determines
how each controller connected to the Modbus network will recognize a message
addressed to it. It also determines the task to be performed and extracts any data or
other information contained in the message. If a reply is required, the controller will
construct a reply message and send it using the Modbus protocol.
The communication technique used in the Modbus protocol is a master-slave
technique. This means that only one device can be the master and initiate transactions,
while other devices connected to the network are slaves and can accordingly not
initiate any transactions.
7.2.1 Communication Connector
The relay equipped with the communication board which provides an RS485
communication ports for Modbus RTU communication support. The communication
port allows the relay REF601 to network with up to 31 other slave REF601 devices
on a Modbus RTU link.
The below diagram shows the connection details for networking of the relay to PC.
7.2 Wiring
REF601
12345
B-
B+
GND
A+
A-
REF601
12345
REF601
12345
RS485 / RS232
Convertor
Tx+
Tx-
Rx+
Rx- G
MODBUS Master
Fig. 43– Connection details for MODBUS RTU communication
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