Multi-Module Communication

At a Glance

This topic explains communication capabilities across modules and devices in a PLC configuration. Different modules and devices are available providing access to USB, Modbus and/or Ethernet communication:

CPU devices with embedded USB, Modbus and/or Ethernet ports
NOE modules for Ethernet communication

Overview

A maximum of two NOE modules can be installed on a PLC configuration.

Therefore, the maximum number of configured Ethernet links is three:

one link via the CPU with embedded Ethernet port
two links via the NOE modules (more are not allowed, even if the CPU configured has no Ethernet port)

The following illustration shows a possible configuration:

This example describes a rack with four modules:

the CPU at rack module address [0.0]
the NOE1 at rack module address [0.1]
the NOE2 at rack module address [0.2]
an I/O module or function module (in this example, we show a DDM 16025 discrete module at rack module address [0.3]).

NOTE: To define the rack/slot combination [x.x]:

first digit = rack number
second digit = slot number

Communication Overview and Definitions

The following illustration presents the overall installation:

In this example, there are:

two NOE modules that are connected to two different Ethernet networks
a CPU that is connected to a third Ethernet network and to a Modbus slave

The following table defines the terms that are used to describe communication methods using multiple communication modules:

Term	Definition
Channel	Represents the communication channel itself, able to manage the dispatching of the messaging flow.
Channel Server	A server dedicated to the management of the communication channel itself. For example, it provides statistical information on an Ethernet link. Control Expert accesses this server to display information related to an NOE module, for example.
CPU Server	This server answers all requests sent to the CPU, whatever the communication media used to access it.

Routing Table

The following table describes the communication capabilities across the different modules:

Destination →	NOE1 Channel Server	NOE1 Channel	NOE2 Channel Server	NOE2 Channel	CPU Ethernet Channel	CPU Modbus Master
Source ↓
NOE1 Channel	supported	not supported	supported	not supported	not supported	supported
NOE2 Channel	supported	not supported	supported	not supported	not supported	supported
CPU Ethernet	supported	not supported	supported	not supported	not supported	supported
CPU USB	supported	supported	supported	supported	supported	supported
CPU Modbus Slave	supported	supported	supported	supported	supported	not supported

Example 1: NOE2 Channel to NOE1 Channel Server

The following illustration describes the connection from an NOE2 channel (source) to an NOE1 channel server (destination). The same methodology can be implemented from an NOE1 channel to an NOE2 channel server:

Example 2: CPU Modbus Slave to NOE Channel, NOE Server Channel, CPU Ethernet Channel

This example describes the connection from a CPU Modbus slave to:

an NOE1 channel server (1)
an NOE2 channel (2)
a CPU Ethernet channel (3)

Example 3: CPU Ethernet to NOE Channel Server, CPU Modbus Master

This example describes the connection from a CPU Ethernet to:

an NOE1 channel server (1)
a CPU Modbus Master (2)

Example 4: Not Supported - NOE1 Channel to NOE2 Channel Not Supported

This example illustrates a configuration that is not supported, with communication from an NOE1 channel to an NOE2 channel: