Mastering Modbus TCP/IP Network Communication

An understanding of Network Layering is essential to grasp why Modbus is able to use TCP/IP for communication.

We look at a real world transportation scenario that can be used to understand Network Layering.

Properties of the Network Layering Analogy Scenario that will exist in Modbus TCP/IP.

A View into the Internal Software Modules that support Network Layering

We look at how layering is used to understand where the TCP/IP software module fits in a device.

We see how the terms client and server take the place (respectively) of master and slave.

We use a cloud icon to represent the inherent complexity of a TCP/IP network.

Ethernet is a Major Component of Modbus TCP/IP

4 Layers that comprise the TCP/IP stack.

How network devices are physically interconnected via Ethernet hardware.

PLC Example revised Interconnection Scheme

We look at 3 main properties of Modbus TCP/IP that cannot be supported on Mobus RS485.

Simultaneous Query Response Cycles on Modbus TCP/IP

Unit ID is supplanted by IP Address on TCP/IP networks.

The lecture explains why the IP address must be used on a Modbus TCP/IP network as opposed to the Unit ID.

Examines the DOT notation used in IP Addresses

A look at the addresses of a number of devices on a network.

A look at the functions of Ports in TCP/IP.

How Modbus uses port 502 for communications.

A look at Ethernet while touching on network arbitration.

Comparison of network arbitration between RS485 and Ethernet.

A look at Carrier Sense Multiple Access / Collision Detection.

Looking at layering again with the new knowledge of Ethernet.

Reminder of having a good working knowledge of standard Modbus.

A look at the difference between the standard Modbus data frame and that which is used in Modbus TCP/IP.

We look at the names of the different parts of the Modbus TCP/IP data frame.

A look at the MBAP header and what the various parts are for.

A look at the MBAP header and what the various parts are for.

A look at how frames are added to the Modbus ADU.

We look at a network with one Modbus TCP/IP client and two Modbus TCP/IP servers.

The Read Input Registers Query Data Stream

The Read Input Registers Response Data Stream

How the transaction identifier changes with every query response cycle.

Basic guidelines for section.

The 2 Modbus software tools are identified are their purposes given.

This lecture identifies the websites from which the Modbus software tools can be downloaded.

This lecture introduces the Modbus Master simulator known as Modscan32. 

This lecture introduces the Modbus Slave simulator known as Modsim32. 

Using the ipconfig command to get ip address of the computer.

How Modscan32 and Modsim32 work as Modbus TCP/IP Simulators

Simulating the Read Input Registers Command.

Data Traffic for the Read Input Registers Command.

Simulating the Read Input Status Command

Data Traffic for the Read Input Status Command

Simulating the Read Holding Registers Command

Data Traffic for the Read Holding Registers Command

Simulating the Read Coils Status Command

Data Traffic for the Read Coils Status Command

Modbus Write Commands

Downloading the CAS Modbus Scanner

Viewing Data Traffic in Hexadecimal Format

Simulating the Force Single Coil Command

Simulating the Preset Single Register Command

Introduction

Overview of the Direct Logic 05 PLC

The 2 Steps to Configuring Modbus on a Physical Device

Looking at the Direct Logic PLC on my desk

Configuration of IP Address on my laptop

Using the NetEdit3 Configuration Software to configure Modbus

Direct Logic 05 Documentation for Modbus Memory Map

Using Modscan32 to Read/Write for Coils