GFK-2224Q January 2017 139
Chapter 9 Modbus/TCP Client
This chapter explains how to program communications over the Ethernet network using Modbus/TCP Channel
commands. This chapter applies only to PLCs being used as client PLCs to initiate Modbus/TCP
communications.
▪ The Communications Request
▪ The COMMREQ Function Block and Command Block
▪ Modbus/TCP Channel Commands
▪ Status Data
▪ Controlling Communications in the Ladder Program
▪ Differences between Series 90 and PACSystems Modbus/TCP Channels
9.1 The Communications Request
“Communications Request” is a term used to describe all the user elements required for correctly initiating
Channel commands in the client. No programming of Communications Requests is required for devices acting
as servers
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