Owners manual

Modbus Protocol User Guide 5
1: Introduction
This protocol manual is for use with Lantronix Industrial Automation Protocol (IAP)
Device Servers, such as the XPress DR-IAP, CoBox-FL-IAP, UDS100-IAP and
UDS10-IAP. In addition to our IAP Device Servers, the Modbus protocol is supported
on various embedded products including versions of the XPort, WiPort, and Micro.
The default protocol in new IAP Device Servers is the Standard Tunneling protocol, a
serial protocol used to connect thousands of intelligent devices to the Ethernet. The
User Guide that comes with your IAP Device Server provides detailed information for
installing and operating the IAP Device Server using Standard Tunnel protocol.
Changing that protocol to one of the industrial protocols changes the configuration
menus and dialogs.
This User Guide provides Modbus™ protocol-specific information for the embedded
and external products listed above.
Modbus
When it comes to planning data communication for open, multi-vendor industrial
control systems, Modbus is the first choice of end users and integrators alike. The
Modbus/RTU protocol defines how a “master” device polls one or more “slave”
devices to read and write data in real time by means of RS232, RS422, or RS485
serial data communication. Although not the most powerful protocol available, its rare
simplicity allows not only rapid implementation but also enough flexibility to apply in
virtually all industrial situations. Modbus/TCP, an extension of Modbus/RTU, defines
how Modbus/RTU and Modbus/ASCII messages are encoded within and transported
over TCP/IP-based networks. Modbus/TCP is just as simple to implement and
flexible to apply as the original Modbus/RTU. You can find the specification for both
online at www.telemecanique.com
.
The IAP Device Server allows users to integrate new and existing Modbus/RTU and
Modbus/ASCII serial devices with newer TCP/IP network-based devices. The next
chapter describes a system that integrates four Modbus/RTU devices with four
Modbus/TCP devices.