Comtrol Modbus TCP User Manual

Modbus®/TCP User Guide

Trademark Notices

Document Number: 2000447 Rev I

Comtrol, DeviceMaster, and PortVision are registered trademarks of Comtrol Corporation.

Concept is a trademark of Schneider Electric.

Modbus is a registered trademark of Schneider Electric.

PLC is a registered trademark of Allen-Bradley Company, Inc.

Ethernet is a registered trademark of Digital Equipment Corporation, Intel, and Xerox Corporation.

Portions of SocketServer are copyrighted by GoAhead Software, Inc. Copyright © 2001. GoAhead Software,
Inc. All Rights Reserved.

Windows is a registered trademark of Microsoft Corporation in the United States and/or other countries.

Other product names mentioned herein may be trademarks and/or registered trademarks of their respective
owners.

Eighth Edition, July 17, 2013
Copyright © 2005-2013. Comtrol Corporation.
All Rights Reserved.

Comtrol Corporation makes no representations or warranties with regard to the contents of this document or
to the suitability of the Comtrol product for any particular purpose. Specifications subject to change without
notice. Some software or features may not be available at the time of publication. Contact your reseller for
current product information.

Table of Contents

Chapter 1. Introduction........................................................................................................7

1.1. Audience ................................................................................................................................................... 7

1.2. Comtrol Modbus Solutions................................................................................................................... 7

1.3. Product Overview .................................................................................................................................. 8

1.4. Modbus/TCP Firmware ......................................................................................................................... 8

1.4.1. Traditional Modbus/TCP System Architecture (Firmware V2.x) .................................................. 8

1.4.2. Enhanced Modbus/TCP System Architecture (Firmware 3.x) ....................................................... 9

1.4.3. Advanced Modbus System Architecture (Firmware 5.x) .............................................................. 10

1.4.4. Modbus/TCP Multi-Mode Connectivity ......................................................................................... 11

1.4.4.1. PLC Master/DeviceMaster UP Slave Mode ......................................................................... 11

1.4.4.2. PLC Slave/DeviceMaster UP Master Mode ......................................................................... 11

1.4.4.3. Dual Master (Virtual Peer-to-Peer) - Write Mode ............................................................... 12

1.4.4.4. Dual Master (Virtual Peer-to-Peer) - Read Mode (Dual Polling) ........................................ 12

1.4.4.5. Filtering and Data Extraction Functionality (Patent Pending) ......................................... 13

1.5. Definitions and Terms......................................................................................................................... 14

1.5.1. Data Type Definitions .................................................................................................................... 14

1.5.2. Glossary........................................................................................................................................... 14

1.6. Locating Updated Software and Documents ................................................................................. 15

1.7. Modbus/TCP Application Setup ........................................................................................................ 15

Chapter 2. Programming Interface..................................................................................17

2.1. Overview................................................................................................................................................. 17

2.1.1. Modbus Master Requirements ....................................................................................................... 17

2.1.2. What is Modbus/RTU?.................................................................................................................... 18

2.1.3. What is Modbus/ASCII? ................................................................................................................. 18

2.1.4. What is Modbus/TCP? .................................................................................................................... 19

2.2. Raw Data Interface .............................................................................................................................. 19

2.2.1. Supported Modbus Messages ......................................................................................................... 19

2.2.2. Serial Port Raw/ASCII Interface ................................................................................................... 20

2.2.3. Ethernet Device Raw/ASCII Interface .......................................................................................... 21

2.2.4. Raw/ASCII Transfer Modes ........................................................................................................... 21

2.2.4.1. Data-Stream Mode ................................................................................................................ 21

2.2.4.2. Command/Response Mode .................................................................................................... 22

2.2.5. Receive Data Message (Raw Data) ................................................................................................ 23

2.2.5.1. Format.................................................................................................................................... 23

2.2.5.2. Communication Methodology (Receive Raw Data in Slave Mode) ..................................... 24

2.2.5.3. Communication Methodology (Receive Data Master Mode) ............................................... 24

2.2.6. Transmit Data Message (Raw Data) ............................................................................................. 25

2.2.6.1. Format.................................................................................................................................... 25

2.2.6.2. Communication Methodology (Transmit Raw Data Slave Mode) ...................................... 26

2.2.6.3. Communication Methodology (Transmit Data Master Mode) ............................................ 26

2.2.7. Sequence Number Messages (Raw Data) ......................................................................................27

2.3. I/O Scanner (Raw Data) ...................................................................................................................... 27

2.4. Modbus/RTU and Modbus/ASCII To-Slaves Protocol Interface ................................................ 29

2.4.1. Communication Methodology......................................................................................................... 29

2.4.2. Modbus Slave Device Search Methodology ...................................................................................30

2.5. Retrieve Statistics Message ............................................................................................................... 31

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Table of Contents - iii

Table of Contents

Chapter 3. Embedded Configuration Pages...................................................................33

3.1. Overview................................................................................................................................................. 33

3.2. Embedded Web Pages Overview ....................................................................................................... 34

3.3. Serial Device Configuration Page .................................................................................................... 35

3.3.1. Edit Serial Port Configuration Page.............................................................................................. 35

3.3.2. Serial Configuration ....................................................................................................................... 36

3.3.3. General Protocol Settings............................................................................................................... 37

3.3.4. Modbus Slave and Raw-Data Device Settings .............................................................................. 38

3.3.5. Serial Port Packet ID Settings (Raw-Data Only).......................................................................... 39

3.4. Ethernet Device Configuration Page............................................................................................... 41

3.5. Edit Socket Port Configuration Page .............................................................................................. 42

3.5.1. Device TCP Connection Configuration .......................................................................................... 42

3.5.2. Socket Packet ID Settings .............................................................................................................. 44

3.6. Common Configuration Areas (Serial or Ethernet Device) ....................................................... 47

3.6.1. Serial Modbus Master and Modbus/TCP Settings........................................................................ 47

3.6.2. Modbus/TCP Master Rx/Tx Settings ............................................................................................. 49

3.6.3. Filtering/Data Extraction Configuration....................................................................................... 51

3.6.4. Application TCP Connection Configuration.................................................................................. 54

3.6.5. Saving Port Options........................................................................................................................ 56

3.7. Edit Network Configuration Page.................................................................................................... 57

3.8. Edit Security Configuration Page .................................................................................................... 58

3.8.1. Client Authentication ..................................................................................................................... 59

3.8.2. Configuring Security ...................................................................................................................... 59

Chapter 4. Diagnostic and Statistics Pages ...................................................................61

4.1. Communication Statistics .................................................................................................................. 62

4.2. PLC Interface Diagnostics ................................................................................................................. 68

4.3. Display All Modbus Slave Devices.................................................................................................... 71

4.4. Display Serial Logs .............................................................................................................................. 73

4.5. Display Ethernet Device Logs ........................................................................................................... 74

Chapter 5. Alias Device ID Functionality.......................................................................75

5.1. Overview................................................................................................................................................. 75

5.2. Alias Modbus Device ID Configuration/Status.............................................................................. 77

5.2.1. Alias Modbus Device ID Configuration/Status Page .................................................................... 77

5.2.2. Add/Modify Alias Device ID Configuration Page .......................................................................... 78

5.2.3. Edit Alias Device ID Configuration Page ...................................................................................... 79

5.2.4. Delete Alias Device ID Configuration Page .................................................................................. 80

5.2.5. Delete All Alias Device ID Configurations Page...........................................................................81

Chapter 6. Troubleshooting and Technical Support ...................................................83

6.1. Troubleshooting Checklist ................................................................................................................ 83

6.2. General Troubleshooting.................................................................................................................... 84

6.3. Technical Support ................................................................................................................................ 84

iv - Table of Contents DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

Table of Contents

Appendix A. Programming the PLC via Concept .........................................................85

A.1. Overview ................................................................................................................................................ 85

A.1.1. What is Concept?............................................................................................................................ 85

A.1.2. Requirements ................................................................................................................................. 85

A.1.3. Example Program Considerations (Raw Data) ............................................................................ 85

A.2. Concept Program Screens ................................................................................................................. 86

A.2.1. Processor and Ethernet Setup ....................................................................................................... 86

A.2.2. Message Screens............................................................................................................................. 87

A.2.2.1. Read Serial Data via Read Holding Registers Message ..................................................... 88

A.2.2.2. Transmit Serial Data via Write Multiple Registers Message ............................................ 89

A.2.2.3. Set Receive Sequence Number via Write Multiple Registers Message ............................. 90

A.2.2.4. Set Transmit Sequence Number via Write Multiple Registers Message .......................... 91

A.2.2.5. Read Serial Port Statistics via Read Holding Registers Message ..................................... 92

A.2.2.6. Modbus/TCP Slot/Index and DeviceMaster UP IP Address Definition ............................. 93

A.2.3. Concept Example Programs .......................................................................................................... 94

A.2.3.1. LPBKCNCP .......................................................................................................................... 94

A.2.3.2. SCANCNCP .......................................................................................................................... 94

A.2.3.3. Setting up and Running the Concept Example Programs ................................................. 95

Appendix B. LPBKCNCP Example Program ...............................................................103

Appendix C. SCANCNCP Example Program ...............................................................109

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Table of Contents - v

Table of Contents

vi - Table of Contents DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

Chapter 1. Introduction

This User Guide provides detailed information about the following topics:

• Programming Interface

• Embedded Configuration Pages

• Diagnostic and Statistics Pages

• Programming the PLC via Concept

• LPBKCNCP Example Program

• SCANCNCP Example Program

The DeviceMaster UP Hardware Installation and Configuration Guide

• Connecting the hardware and devices

• Programming the DeviceMaster UP IP address,

• Uploading Modbus/TCP firmware

The Modbus/TCP
procedures.

See Locating Updated Software and Documents
tools.

Interface Configuration Quick Start provides embedded web page configuration

on Page 17

on Page 33

on Page 61

on Page 85

on Page 103

on Page 109

provides the following information:

on Page 15 to locate the latest firmware, documentation, and

1.1. Audience

The primary audience of this document is the person responsible for installing the DeviceMaster UP and
programming the PLC. This guide assumes you are familiar with the following topics:

• Windows operating system

• Modbus/TCP, Modbus/RTU, and/or Modbus/ASCII

• A PLC, SCADA System, or OPC Server that communicates with Modbus/TCP, Modbus/RTU, or Modbus/
ASCII

- Raw/ASCII devices such as barcode scanners, weigh scales, and printers

- Modbus/RTU and/or Modbus/ASCII slave devices.

1.2. Comtrol Modbus Solutions

If you ordered the Modbus part number for your DeviceMaster UP, Modbus/TCP is loaded on the
DeviceMaster UP by default. You may want to review our other Modbus solutions to make sure that the
feature rich Modbus/TCP application is what you want to use. Optionally, Modbus Router or Modbus Server
may by more effective for your particular environment.

The Comtrol web site provides information about the differences between the three Modbus solutions:

• M

ODBUS/TCP

• M

ODBUS SERVER

• M

ODBUS ROUTER

In addition, the DeviceMaster UP product CD and ftp site also provide these documents for your reference.

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 1. Introduction - 7

Product Overview

The following links function if you are reading this document from the ftp site or CD.

Note: Optionally, open the CD and click Modbus. The main page (

links to these documents.

• Modbus Controller to Controller Communication

• Modbus Solution Examples

• Providing Read-Only Modbus Protection

• Resolving Modbus Device ID Conflicts

If Modbus Server or Modbus Router is a better solution, you can
corresponding documentation.

up_modbus_family_main.htm) provides

DOWNLOAD the appropriate firmware and

1.3. Product Overview

The DeviceMaster UP operates as a highly versatile Modbus gateway when the Modbus/TCP firmware is
uploaded to the DeviceMaster UP. The DeviceMaster UP provides Modbus/TCP, Modbus/RTU, Modbus/
ASCII, and Ethernet TCP/IP controller interfaces to both serial and Ethernet TCP/IP raw/ASCII devices, and
both Modbus/RTU and Modbus/ASCII slave devices.

Your particular DeviceMaster UP model may or may not have the Modbus/TCP firmware loaded (depending
on the model you purchased).

Note: Models that have Modbus/TCP loaded on the DeviceMaster UP are identified in PortVision DX and the

DeviceMaster UP is labeled accordingly.

1.4. Modbus/TCP Firmware

The following subsections provide information for existing users who may or may not want to update systems
with the advanced Modbus/TCP firmware 5.0x. For new users, the following subsections provide Modbus
system architecture information.

1.4.1. Traditional Modbus/TCP System Architecture (Firmware V2.x)

Modbus/TCP firmware V2.x provided a traditional Modbus/TCP slave interface to devices through a raw/
ASCII or Modbus/RTU serial interface as illustrated.

8 - Chapter 1. Introduction DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

Enhanced Modbus/TCP System Architecture (Firmware 3.x)

1.4.2. Enhanced Modbus/TCP System Architecture (Firmware 3.x)

Using the Modbus/TCP firmware V3.x doubles the capacity of the DeviceMaster UP by providing a raw/ASCII
interface to both serial and Ethernet TCP/IP devices. At the same time, the DeviceMaster UP continues to
provide a traditional Modbus/TCP to Modbus/RTU interface for Modbus/RTU slave devices.

• Improved PLC interfaces:

- Transfer of large received serial device packets up to 1024 bytes in Master Receive mode.

- Transfer of large received Ethernet device packets up to 2048 bytes in Master Receive mode.

- Throttling of received data to the PLC in the Master Receive mode.

- Ensures data received by the PLC is not overwritten before it can be processed.

- Disabling of non-filtered receive queue, ensures the PLC will only receive the latest received serial/

Ethernet device data.

• New embedded web pages

- PLC Interface Diagnostics page provides statistics and error messages to monitor and help diagnose

PLC interface problems.

- Serial/Ethernet Device Communication Statistics page is a comprehensive statistics page for all serial

and Ethernet device interfaces. Includes packet, byte, and error counts to the PLC(s) and
application(s) as well as comprehensive filtering statistics.

- Ethernet Device Interface Configuration page provides a user interface to the Ethernet device

interface configuration.

For example:

• The DeviceMaster UP 1-port provides Modbus/TCP support for one raw/ASCII or Modbus/RTU serial
device and one raw/ASCII Ethernet device for a total of two devices.

• The DeviceMaster UP 2-port provides Modbus/TCP support for two raw/ASCII or Modbus/RTU serial
device and two raw/ASCII Ethernet device for a total of four devices.

• The DeviceMaster UP 4-port provides Modbus/TCP support for four raw/ASCII or Modbus/RTU serial
devices and four raw/ASCII Ethernet devices for a total of eight devices.

Modbus/TCP firmware 3.x provides an application interface for both serial and Ethernet raw/ASCII devices.
You can connect any application, such as a configuration, database, or control application, via the application
socket port to raw/ASCII serial and/or Ethernet devices while the device(s) are attached to the PLC via
Modbus/TCP.

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 1. Introduction - 9

Advanced Modbus System Architecture (Firmware 5.x)

DeviceMaster UP

1.4.3. Advanced Modbus System Architecture (Firmware 5.x)

Using the Modbus/TCP V5.x firmware provides greatly enhances connectivity options. New options include:

• New Modbus support:

- Modbus/ASCII serial slave device support.

- Modbus/RTU and Modbus/ASCII serial master support. Modbus/RTU and Modbus/ASCII masters
can now connect to Modbus/RTU serial slaves, Modbus/ASCII serial slaves, and both serial and
Ethernet TCP/IP raw/ASCII devices.

• New raw/ASCII functionality:

- Selectable Message Transfer mode

- Data-Stream - Transmit all message to devices immediately. Return all receive data/responses to all
PLC and Application Ethernet TCP/IP connections.

- Command/Response - Transmit messages one command at a time and wait for response(s). Return all
response(s) to command sender only.

This version of the firmware allows up to six Application Ethernet TCP/IP connections for each serial or
socket port configuration. (Device Ethernet TCP/IP configurations still only allow one connection per device.)

10 - Chapter 1. Introduction DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

Modbus/TCP Multi-Mode Connectivity

1.4.4. Modbus/TCP Multi-Mode Connectivity

The Modbus/TCP firmware 5.x supports the following Modbus/TCP communication modes:

• PLC Master/DeviceMaster UP Slave Mode

• PLC Slave/DeviceMaster UP Master Mode

• Dual Master (Virtual Peer-to-Peer) - Write Mode

• Dual Master (Virtual Peer-to-Peer) - Read Mode (Dual Polling)

• Filtering and Data Extraction Functionality (Patent Pending)

1.4.4.1. PLC Master/DeviceMaster UP Slave Mode

PLC Master/DeviceMaster
UP Slave mode:

• Standard Modbus

master to slave device
method of
communication. All
read and write
messages are initiated
by the Modbus master.

•Raw/ASCII, Modbus/

RTU slave, and
Modbus/ASCII slave
devices are supported in
this mode.

• For raw/ASCII mode, the Receive Transfer mode and Transmit Transfer mode are both set to Slave (In

Modbus/RTU-to-Slaves and Modbus/ASCII-to-Slaves mode, the DeviceMaster UP port only operates in
To-Slave mode.

on Page 11

on Page 11

on Page 12

on Page 12

on Page 13

1.4.4.2. PLC Slave/DeviceMaster UP Master Mode

PLC slave/DeviceMaster UP
master mode:

• The DeviceMaster UP

initiates all read and
write messages.

• The DeviceMaster UP

writes received serial
and/or Ethernet device
data directly into PLC
memory with minimal
latency.

• The DeviceMaster UP

polls the PLC for transmit data for serial and/or Ethernet devices.

• PLC programs can be simplified to eliminate both polling for received data and sending of write messages

to transmit data.

• Only raw/ASCII devices are supported in this mode.

• The DeviceMaster UP Receive Transfer mode and Transmit Transfer mode are both set to Master.

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 1. Introduction - 11

Dual Master (Virtual Peer-to-Peer) - Write Mode

1.4.4.3. Dual Master (Virtual Peer-to-Peer) - Write Mode

Dual master (virtual peer-to­peer) - write mode:

• The DeviceMaster UP
and PLC initiate only
write messages to each
other.

• The DeviceMaster UP
writes received serial
and/or Ethernet device
data directly into PLC
memory with minimal
latency.

• The PLC can write to
serial and/or Ethernet devices through the DeviceMaster UP with minimal latency.

• This mode provides the lowest possible Ethernet bandwidth usage and most efficient usage of PLC and
DeviceMaster UP processing power.

• Only raw/ASCII devices are supported in this mode.

•The DeviceMaster UP Receive Transfer mode is set to Master and Transmit Transfer mode is set to Slave.

1.4.4.4. Dual Master (Virtual Peer-to-Peer) - Read Mode (Dual Polling)

Dual master (virtual peer-to­peer) - read mode (dual
polling):

• This is provided for
programmers who
strongly prefer polling.

• The DeviceMaster UP
and PLC initiate only
read messages to each
other.

• The PLC will poll for
received serial and/or
Ethernet device data.

• The DeviceMaster UP polls for transmit data to serial and/or Ethernet devices.

• This mode requires the highest possible Ethernet bandwidth usage and provides the least efficient usage
of PLC and DeviceMaster UP processing power.

• Only raw/ASCII devices are supported in this mode.

• The DeviceMaster UP Receive Transfer mode is set to Slave and Transmit Transfer mode is set to Master.

12 - Chapter 1. Introduction DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

Filtering and Data Extraction Functionality (Patent Pending)

1.4.4.5. Filtering and Data Extraction Functionality (Patent Pending)

The DeviceMaster UP provides the following filtering and data extraction functionality.

•Filtering:

- String Filtering of up to 128 bytes of raw/ASCII data to both the PLC and/or application.

- RFID filtering of EPCglobal formatted RFID tag data to both the PLC and/or application.

- Barcode filtering of all UPC/EAN formatted barcodes data to both the PLC and/or application.

- Simplifies PLC and application programming tasks.

• Data Extraction:

- RFID data extraction extracts all parameters, such as company code, product code, and serial
numbers, from any or all of the 43 EPCglobal tag formats. It then transfers the data to the PLC and/
or application in a consistent and simple format.

- Barcode data extraction extracts the company, product, and numbering codes from UPC/EAN
formatted barcodes. It then transfers the data to the PLC and/or application in a consistent and
simple format.

- Simplifies PLC and application programming tasks.

• Environment specific support:

- Support for multiple RFID reader tag formats.

- RFID antenna grouping.

- Aging of filtered string/RFID/barcode entries.

- Discarding of unrecognized RFID and barcode messages.

For detailed information about filtering and data extraction, see the DeviceMaster UP Filtering and Data

Extraction Reference Guide.

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 1. Introduction - 13

Definitions and Terms

1.5. Definitions and Terms

This section describes the Modbus/TCP definitions and terms included in the Modbus/TCP interface and
supported by the DeviceMaster UP.

1.5.1. Data Type Definitions

The following list defines the available data types.

Data Type Definition

BYTE Bit String (8-bits)

DINT Signed Double Integer (32-bits)

DWORD Bit String (32-bits)

INT Signed Integer (16-bits)

STRING Character String (1-byte per character)

UDINT Unsigned Double Integer (32-bits)

USINT Unsigned Short Integer (8-bits)

WORD Unsigned Integer (16-bits)

1.5.2. Glossary

The following list defines terms associated with Modbus/TCP.

Term Definition

Alias Device ID

Device ID

Ethernet Device A device that communicates through an Ethernet TCP/IP connection.

Master Device

Modbus

Modbus Serial The Modbus protocol over a serial connection.

Modbus/ASCII

Modbus/RTU Modbus Serial in binary format.

Modbus/TCP

Raw Serial
Device

Slave Address The address of the slave device. This term is identical to Unit Identifier and Device ID.

Slave Device A device that only responds to Modbus messages.

Socket Port The Ethernet socket port that is used to communicate to an Ethernet device.

The device ID that the original received ID is changed to when an Alias Device ID is
configured.

The address of the slave device and the term is identical to Unit Identifier and Slave
Address.

A device that transmits Modbus/TCP messages to slave devices and receives the
corresponding responses.

An application layer messaging protocol that provides client/server communications
between devices connected on different types of buses.

Modbus Serial in ASCII format. This form of Modbus communication requires two
characters for each byte.

The Modbus protocol over an Ethernet TCP/IP connection. Also known as Modbus over
Ethernet.

A common serial device that communicates over serial ports through plain byte or ASCII
data messages.

14 - Chapter 1. Introduction DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

Locating Updated Software and Documents

Term Definition (Continued)

Unit Identifier The address of the slave device and the term is identical to Device ID and Slave Address.

1.6. Locating Updated Software and Documents

You can access the firmware software assembly, PortVision DX, and the DeviceMaster UP documentation
from the CD shipped with the DeviceMaster UP or you can download the latest files from:

ftp://ftp.comtrol.com/html/up_modbus_tcp_main.htm

1.7. Modbus/TCP Application Setup

Before you can configure the Modbus/TCP firmware on the DeviceMaster UP, you must have previously
performed the following steps:

• Install the hardware

• Install PortVision DX

• If necessary, upload the Modbus/TCP firmware using PortVision DX

Note: Models that have Modbus/TCP loaded on the DeviceMaster UP are identified in PortVision DX and

the DeviceMaster UP is labeled accordingly.

• Configure the DeviceMaster UP IP address using PortVision DX

Note: If necessary, refer to the DeviceMaster UP Hardware Installation and Configuration Guide

above procedures.

Use the following steps to complete the DeviceMaster UP configuration for Modbus/TCP.

1. Program the Modbus/TCP PLC (refer to the information in Programming Interface

2. Configure the DeviceMaster UP serial and Ethernet device interface settings using the Modbus/TCP

Interface Configuration Quick Start. You can use Embedded Configuration Pages on Page 33) as a

reference if you need additional information about fields on the web pages.

3. Connect your serial device or devices and make sure all Ethernet devices are attached to the same
Ethernet subnet. If necessary, refer to the DeviceMaster UP Hardware Installation and Configuration

Guide.

on Page 17).

for the

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 1. Introduction - 15

Modbus/TCP Application Setup

16 - Chapter 1. Introduction DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

Chapter 2. Programming Interface

2.1. Overview

The DeviceMaster UP provides highly flexible Modbus connectivity.

• Modbus masters supported include Modbus/TCP and Modbus/RTU and Modbus/ASCII serial masters.

• Both serial Modbus/RTU and Modbus/ASCII slave devices are supported.

• All Modbus masters can communicate with all Modbus slave devices.

• The Modbus/RTU and Modbus/ASCII Protocol Interface is defined in (2.4.

ASCII To-Slaves Protocol Interface on Page 29).

The DeviceMaster UP provides highly advanced raw/ASCII device functionality:

• Both serial and Ethernet TCP/IP devices are supported.

• Modbus interfaces include Modbus/TCP masters, Modbus/TCP slaves, and both Modbus/RTU and
Modbus/ASCII serial masters.

• Up to six Ethernet TCP/IP Application connections per serial or Ethernet TCP/IP device.

• The raw/ASCII interface is defined in (2.2.

You must configure the DeviceMaster UP through its embedded web pages defined in Chapter 3.

Configuration Pages on Page 33.

The DeviceMaster UP uses normal Modbus addressing conventions and provides receive, transmit, and
statistical data.

Appendix A.

examples provided with the DeviceMaster UP. It describes how to configure the DeviceMaster UP for raw
serial data and start running the example programs using the embedded web pages and the example PLC
program code.

Note: While the Concept PLC example programs directly apply only to the Schneider Electric Momentum,

Programming the PLC via Concept on Page 85 describes the Concept™ PLC programming

Quantum, and Compact PLCs, they can be used as a guide for programming other PLCs.

Raw Data Interface on Page 19).

Modbus/RTU and Modbus/

Embedded

2.1.1. Modbus Master Requirements

Modbus Masters (Modbus/TCP, Modbus/RTU serial, and Modbus/ASCII) must meet these requirements:

• The Modbus Master must support the corresponding protocol.

• For raw/ASCII data, the Modbus Master must support the Read Holding Registers and Write Multiple
Registers commands or, alternatively, the Read/Write Multiple Registers command.

• The Modbus Master must be able to write enough data in one message to handle the maximum sized
messages required for the serial or Ethernet device.

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 2. Programming Interface - 17

What is Modbus/RTU?

2.1.2. What is Modbus/RTU?

Modbus/RTU is native Modbus in hexadecimal format. These are the base Modbus messages that contain
simple read and write requests. The format is as follows:

Where:

• The terms Master or Client are used to identify the sender of the message.

• The terms Slave or Server are used to identify the devices responding to the message.

Modbus/RTU is used primarily for:

• Serial port connectivity. RS-485 is the most common serial mode, but RS-232 and RS-422 are also widely
used. Commonly used by both Master and Slave devices.

• Ethernet TCP/IP socket connections. This is not the same as Modbus/TCP (please see section on Modbus/
TCP), but does provide a very simple method of interfacing to remote devices. It is used by many
applications and some OPC servers.

Note: This communication method typically is not supported by PLCs.

2.1.3. What is Modbus/ASCII?

Modbus/ASCII is native Modbus in ASCII format. This protocol is used primarily by legacy devices and is no
longer supported as widely as Modbus/RTU.

Like Modbus/RTU, Modbus/ASCII contains the base Modbus messages that contain simple read and write
requests. The differences between Modbus/ASCII and Modbus/RTU are:

1. The message data is sent in ASCII format, so the message length is twice as long. It requires two ASCII
characters for each byte of data.

2. An 8 bit LRC is attached to verify the message instead of a 16 bit CRC. The LRC is also transmitted in
ASCII format.

3. There are defined starting and ending characters to determine a Modbus/ASCII messages.

The format is as follows:

Where:

• The terms Master or Client are used to identify the sender of the message.

• The terms Slave or Server are used to identify the devices responding to the message.

Modbus/ASCII is used primarily for:

• Serial port connectivity. RS-485 is the most common serial mode, but RS-232 and RS-422 are also used.
Used primarily by legacy Slave devices.

• Ethernet TCP/IP socket connections. This is not the same as Modbus/TCP (please see section on Modbus/
TCP), but does provide a very simple method of interfacing to remote devices. It is used by some
applications and some OPC servers.

Note: This communication method typically is not supported by PLCs.

18 - Chapter 2. Programming Interface DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

What is Modbus/TCP?

2.1.4. What is Modbus/TCP?

Modbus/TCP is an Ethernet network based protocol that contains a Modbus/RTU message, with the exception
of the 2 byte CRC. The Modbus/TCP message contains a header with information designed to provide message
identification and routing information. The format is as follows:

Where:

• The terms Master or Client are used to identify the sender of the message.

• The terms Slave or Server are used to identify the devices responding to the message.

• Modbus TCP messages are typically sent to and received on a defined Ethernet TCP/IP socket of 502.

• Modbus TCP implementations provide more capability, but also require more processing than simpler
Modbus/RTU implementations.

Modbus TCP is used for connecting advanced Ethernet based devices, such as PLCs, HMIs, SCADA Systems,
and most OPC Servers to:

• Other Ethernet devices supporting Modbus TCP.

• Serial Modbus/RTU and/or Modbus/ASCII devices through gateways (such as the DeviceMaster UP
running the Modbus/TCP or Modbus Router applications).

• Serial or Ethernet TCP/IP raw/ASCII devices (barcode scanners, printers, RFID readers, visions systems,
etc) through a gateway (such as the DeviceMaster UP running the Modbus/TCP application).

2.2. Raw Data Interface

This subsection contains the following topics:

• Supported Modbus Messages

• Serial Port Raw/ASCII Interface

• Ethernet Device Raw/ASCII Interface

• Receive Data Message

• Transmit Data Message

• Sequence Number Messages

(Raw Data) on Page 23

2.2.1. Supported Modbus Messages

DeviceMaster UP supports the following Modbus messages over Modbus/TCP for raw data transfer.

Message Type Function Code Maximum Message Size Maximum Serial Packet Size

Read Holding Registers 3 250 BYTEs (125 WORDs) 246 BYTEs (123 WORDs)

Write Multiple Registers 16 (10 hex) 240 BYTEs (120 WORDs) 236 BYTEs (118 WORDs)

Read/Write Multiple
Registers

on Page 19

on Page 20

on Page 21

(Raw Data) on Page 25

(Raw Data) on Page 27

23 (17 hex) 236 BYTEs (118 WORDs) 232 BYTEs (116 WORDs)

Note: Your PLC programming software may not allow maximum size serial packets.

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 2. Programming Interface - 19

Serial Port Raw/ASCII Interface

2.2.2. Serial Port Raw/ASCII Interface

Serial Port

Raw/ASCII

Addressing

Unit ID 255 (FF hex) 255 (FF hex) 255 (FF hex) 255 (FF hex) N/A

Receive Data
Address

Receive Data
Sequence
Number Address

Transmit Data
Address

Transmit Data
Sequence
Number Address

Statistics
Address

Serial Port 1 Serial Port 2 Serial Port 3 Serial Port 4 Access Rule

1000 (Base 0)
1001 (Base 1)

1256 (Base 0
1257 (Base 1)

1300 (Base 0)
1301 (Base 1)

1556 (Base 0)
1557 (Base 1)

1600 (Base 0)
1601 (Base 1)

2000 (Base 0)
2001 (Base 1)

2256 (Base 0
2257 (Base 1)

2300 (Base 0)
2301 (Base 1)

2556 (Base 0)
2557 (Base 1)

2600 (Base 0)
2601 (Base 1)

3000 (Base 0)
3001 (Base 1)

3256 (Base 0
3257 (Base 1)

3300 (Base 0)
3301 (Base 1)

3556 (Base 0)
3557 (Base 1)

3600 (Base 0)
3601 (Base 1)

4000 (Base 0)
4001 (Base 1)

4256 (Base 0
4257 (Base 1)

4300 (Base 0)
4301 (Base 1)

4556 (Base 0)
4557 (Base 1)

4600 (Base 0)
4601 (Base 1)

Read Only

Read/Write

Read/Write

Read/Write

Read/Write

20 - Chapter 2. Programming Interface DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

2.2.3. Ethernet Device Raw/ASCII Interface

Ethernet Device Raw/ASCII Interface

Socket Port Raw
Data Addressing

Socket Port 1 Socket Port 2 Socket Port 3 Socket Port 4 Access Rule

Unit ID 254 (FE hex) 254 (FE hex) 254 (FE hex) 254 (FE hex) N/A

Receive Data
Address

Receive Data
Sequence Number
Address

Transmit Data
Address

Transmit Data
Sequence Number
Address

1000 (Base 0)
1001 (Base 1)

1256 (Base 0
1257 (Base 1)

1300 (Base 0)
1301 (Base 1)

1556 (Base 0)
1557 (Base 1)

2000 (Base 0)
2001 (Base 1)

2256 (Base 0
2257 (Base 1)

2300 (Base 0)
2301 (Base 1)

2556 (Base 0)
2557 (Base 1)

3000 (Base 0)
3001 (Base 1)

3256 (Base 0
3257 (Base 1)

3300 (Base 0)
3301 (Base 1)

3556 (Base 0)
3557 (Base 1)

4000 (Base 0)
4001 (Base 1)

4256 (Base 0
4257 (Base 1)

4300 (Base 0)
4301 (Base 1)

4556 (Base 0)
4557 (Base 1)

Read Only

Read/Write

Read/Write

Read/Write

2.2.4. Raw/ASCII Transfer Modes

The DeviceMaster UP supports two different raw/ASCII message transfer modes. The default Data-Stream
mode is the traditional transfer mode that asynchronously transmits messages and returns received data/
responses. The Command/Response mode provides a synchronous transfer mode for sending and returning
responses.

2.2.4.1. Data-Stream Mode

The Data-Stream transfer mode is the default transfer mode that asynchronously transmits messages from
all Modbus and Application interfaces and returns received data/responses to all Modbus and Application
interfaces. This mode is typically used in installations that utilize only one controller and for receive-only
devices such as barcode scanners, RFID readers, weigh scales, and position encoders.

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 2. Programming Interface - 21

Command/Response Mode

2.2.4.2. Command/Response Mode

The Command/Response mode provides the following functionality:

• A synchronous transfer mode for sending and returning responses from all Modbus and Application
Ethernet TCP/IP interfaces to serial and Ethernet TCP/IP devices.

• Only one command message is transmitted at a time. Command messages are queued if a command
message is active.

• Responses are routed only to the message sender.

• Responses are timed out and old responses, (ones not requested within a certain time frame), destined for
the Modbus interface are discarded.

• The expected response count is configurable. While this is typically one, some devices may return multiple
responses per message.

The Command/Response transfer mode is typically required in installations that require multiple controllers
sending raw/ASCII messages with expected responses, and it is desired that each controller only receive its
own responses.

22 - Chapter 2. Programming Interface DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

Receive Data Message (Raw Data)

2.2.5. Receive Data Message (Raw Data)

The following topics are discussed:

• Format

• Communication Methodology (Receive Raw Data in Slave Mode)

• Communication Methodology (Receive Data Master Mode)

2.2.5.1. Format

The Receive Data message for raw data contains a simple protocol including a sequence number, length and
serial data fields. The Modbus standard requires a WORD format.

The following table displays the format of the Receive Data message.

on Page 23

on Page 24

on Page 24

Name Data Type Data Value(s) Access Rule

Receive (to PLC) message data.

Structure of:

Produced data sequence
Data length (in bytes)

Data array

WORD
WORD

Array of WORD

0-65535 (FFFF hex)
0-246 (slave Rx mode)

1-1024 (serial Rx master)
1-2048 (Ethernet Rx master)

0-65535

Read only

Receive messages have the following characteristics:

• It returns all data in WORDs.

• The DeviceMaster UP increments the sequence number when it returns new data.

• The message received from the PLC determines the actual length of the Modbus message returned to the
PLC. (This is often greater than the length of the actual number of valid bytes in the Receive Data
Message.)

• All unused bytes in a Modbus message returned to the PLC are filled with zeroes.

• The default order of the bytes is Least Significant Byte First. However, you can select the Rx MS Byte

First option in the web page to return bytes by Most Significant Byte First. For more information, see Rx
MS Byte First under 3.3.5.

Serial Port Packet ID Settings (Raw-Data Only) on Page 39.

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 2. Programming Interface - 23

Communication Methodology (Receive Raw Data in Slave Mode)

2.2.5.2. Communication Methodology (Receive Raw Data in Slave Mode)

Raw serial and/or EtherNet
device data is returned in
the response to the Read
Holding Registers message
or, optionally, the Read/
Write Multiple Register
message. The data is
requested by accessing the
corresponding receive data
address for the desired port.

The following restrictions
apply to this method:

•The Device Index must be 255 (FF hex) for raw/ASCII serial data and 254 (FE hex) for raw/ASCII
Ethernet device data.

• The variable to receive the data on the PLC must be:

- In the 40xxxx address range. (For Modicon type PLCs.)

- An array of 16 bit words.

- Of sufficient size to contain the sequence number, length, and data field associated with the received

data structure. For more information, see the 2.2.5.

Receive Data Message (Raw Data) definition on

Page 23.

• New data will be indicated with an incremented sequence number.

The same data may be returned more than once. However, the same data packet will also return the same
sequence number.

• No data will be indicated with a length of zero.

2.2.5.3. Communication Methodology (Receive Data Master Mode)

Raw serial and/or Ethernet
device data is written to the
PLC at the configured
address.

The following restrictions
apply to this method:

•The Device Index must be
configured for the target
PLC.

• The variable to receive
the data on the PLC
must be:

- In the 40xxxx. (For Modicon type PLCs.)

- An array of 16 bit words.

- Of sufficient size to contain the sequence number, length, and data field associated with the received

data structure.

• New data will be indicated with an incremented sequence number.

24 - Chapter 2. Programming Interface DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

Transmit Data Message (Raw Data)

2.2.6. Transmit Data Message (Raw Data)

The following topics are discussed:

• Format

• Communication Methodology (Transmit Raw Data Slave Mode)

• Communication Methodology (Transmit Data Master Mode)

2.2.6.1. Format

The Transmit Data message for raw data contains a simple protocol including a sequence number, length and
serial data fields. The Modbus standard requires a WORD format.

The following table displays the format of the Transmit Data message.

on Page 25

on Page 26

on Page 26

Name Data Type Data Value(s) Access Rule

Transmit (PLC to DeviceMaster UP)
message data.

Structure of:

Produced data sequence
Data length (in bytes)

Data array

WORD
WORD

Array of WORD

0-65535 (FFFF hex)
1-236 (Slave Tx Mode)
1-246 (Master Tx Mode)
0-65535

Read/Write

Transmit messages have the following characteristics:

• It transfers all data in WORDs.

•If the Disable Tx Sequence Number Check option is not selected, the sequence number must be incremented

when there is new data to transmit.

• The data length field indicates the number of valid bytes contained in the message.

• The actual length of a message received from the PLC may contain extra, unused data.

• It ignores all unused bytes in a Modbus message.

• The default order of the bytes is Least Significant Byte First. However, you can select the Tx MS Byte First
option in the web page to transmit bytes by Most Significant Byte First. For more information, see Tx MS

Byte First under 3.3.5.

Serial Port Packet ID Settings (Raw-Data Only) on Page 39.

• A request for the Transmit data returns the last transmit data message.

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 2. Programming Interface - 25

Communication Methodology (Transmit Raw Data Slave Mode)

2.2.6.2. Communication Methodology (Transmit Raw Data Slave Mode)

Raw serial and/or EtherNet
device data is sent in the
Write Multiple Registers
message or, optionally, the

Read/Write Multiple
Register message. The data

is requested by accessing
the corresponding transmit
data address for the desired
port.

The following restrictions
apply to this method:

•The Device Index must be 255 (FF hex) for raw/ASCII serial data and 254 (FE hex) for raw/ASCII
Ethernet device data.

• The variable to transmit the data on the PLC must be:

- In the 40xxxx address range. (For Modicon type PLCs.)

- An array of words.

- Of sufficient size to contain the sequence number, length, and data field associated with the transmit

data structure, typically 128 words. See 2.2.6.

Transmit Data Message (Raw Data) on Page 25 for

more information.

•If the Disable Tx Sequence Number Check option is not selected, the sequence number must be incremented
when there is new data to transmit. The same transmit data message may be sent to the DeviceMaster
UP more than once. However, the data packet will only be transmitted when a new sequence number is
received.

2.2.6.3. Communication Methodology (Transmit Data Master Mode)

Raw serial and/or Ethernet
transmit data is polled from
the PLC at the configured
address and, when the
DeviceMaster UP receives a
transmit message with an
updated sequence number,
the data is transmitted to
the serial or Ethernet
device.

• The following
restrictions apply to this
method:

•The Device Index must be configured for the target PLC.

• The variable to receive the data on the PLC must be:

- In the 40xxxx. (For Modicon type PLCs.)

- An array of 16 bit words.

- Of sufficient size to contain the sequence number, length, and data field associated with the transmit

data structure.

• The PLC will indicate new data to transmit with an incremented sequence number. (The Disable Tx
Sequence Number Check option does not apply to transmit data master mode.)

• The length will indicate the number of bytes to transmit.

• The DeviceMaster UP will expect the length parameter and data to transmit to be updated before the
transmit sequence number is incremented. Therefore, as soon as the DeviceMaster UP receives an
incremented transmit number, it will transmit the data to the serial or Ethernet device.

26 - Chapter 2. Programming Interface DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

Sequence Number Messages (Raw Data)

2.2.7. Sequence Number Messages (Raw Data)

Read Holding Registers and Write Multiple Register messages can read and modify both receive and transmit
produced data sequence numbers. These are the same sequence numbers returned to the PLC in the Receive
Data Message and sent to the DeviceMaster UP in the Transmit Data message. Access to these sequence
numbers are provided primarily for initialization purposes at the start of the PLC program when you may
want to initialize the sequence numbers on the PLC, DeviceMaster UP or both.

2.3. I/O Scanner (Raw Data)

The I/O Scanner is an optional
PLC communications method
that is implemented on some
PLC programming software
such as the Concept
programming package for use
with the Schneider Electric
Modicon PLCs. The I/O
Scanner provides a rather
simple method that requires
minimal programming effort. It
automatically performs the
polling and transmitting of
data at set time intervals and typically utilizes the Read/Write multiple Registers message.

The following restrictions apply to this method:

•The Receive and Transmit mode for the serial and/or Ethernet device must both be set to Slave mode.

•The Device Index must be 255 (FF hex) for raw/ASCII serial data and 254 (FE hex) for raw/ASCII
Ethernet device data.

• The variable to receive the data on the PLC must be:

- In the 40xxxx address range. (For Modicon type PLCs.)

- An array of words.

- Of sufficient size to contain the sequence number, length, and data field associated with the received

data structure, typically 128 words. For more information, see the 2.2.5.

Data) definition on Page 23.

• New received data will be indicated with an incremented sequence number.

The same data may be returned more than once. However, the same data packet will also return the same
sequence number.

• No receive data will be indicated with a length of zero.

• The variable to transmit the data on the PLC must be:

- In the 40xxxx address range. (For Modicon PLCs.)

- An array of words.

- Of sufficient size to contain the sequence number, length, and data field associated with the transmit

data structure, typically 128 words. See 2.2.6.
more information.

•If the Disable Tx Sequence Number Check option is not selected, the sequence number must be incremented
when there is new data to transmit.

The same transmit data message may be sent to the DeviceMaster UP more than once. However, the data
packet will only be transmitted when a new sequence number is received.

• The DeviceMaster UP should be reset before starting a PLC program using the I/O Scanner due to PLC
program execution scheduling. If the DeviceMaster UP is not reset, the sequence numbers may be out of
sync. This may result in receiving outdated serial data as well as an unexpected transmission of serial
data. A Transmit Unexpected Sequence Number error may also occur.

Transmit Data Message (Raw Data) on Page 25 for

Receive Data Message (Raw

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 2. Programming Interface - 27

I/O Scanner (Raw Data)

The following depicts a typical I/O Scanner screen.

28 - Chapter 2. Programming Interface DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I

Modbus/RTU and Modbus/ASCII To-Slaves Protocol Interface

2.4. Modbus/RTU and Modbus/ASCII To-Slaves Protocol Interface

The DeviceMaster UP provides access to serial Modbus/RTU and Modbus/ASCII slave devices via Modbus/
TCP, serial Modbus/RTU masters, and serial Modbus/ASCII masters. Modbus master messages are
translated to Modbus/RTU or Modbus/ASCII messages, devices are automatically located, and appropriate
Modbus responses are returned to the Modbus masters.

2.4.1. Communication Methodology

The DeviceMaster UP translates Modbus master messages into Modbus/RTU or Modbus/ASCII messages and
forwards them to slave devices attached to the Modbus/RTU or Modbus/ASCII slave serial ports. Each
Modbus message is transmitted and a response is expected. The DeviceMaster UP times out the Modbus/RTU
or Modbus/ASCII messages if there is no response returned within the configured timeout period.

The following diagram displays the Modbus message transfer.

The following apply to Modbus slaves serial ports.

• All valid Modbus master messages are translated to Modbus slave messages for serial port transmission.

• Modbus slave devices are automatically located on a DeviceMaster UP 2-port or 4-port.

• Messages are timed out if no response is returned within the configured timeout period.

• Appropriate Modbus responses are returned to the Modbus master.

• Broadcast Modbus messages, those with a unit identifier of zero, are transmitted out all Modbus slave
serial ports on the DeviceMaster UP.

The following restrictions apply to the Modbus slave interface:

• The DeviceMaster UP serves as a slave Modbus/TCP device, a master on Modbus To-Slaves serial ports,
and a slave on Modbus To-master serial ports.

• All Modbus slave devices attached to a DeviceMaster UP gateway (1, 2, or 4-port) must have unique Unit
Identifiers. Valid Unit Identifiers are 1 to 247 and the Broadcast Identifier is zero.

To communicate to Modbus slave device(s) through a DeviceMaster UP, perform the following steps.

1. Using the embedded web page, select the appropriate Port.

2. Under Serial Configuration, configure the serial port parameters such as the Mode, Baud rate, Data Bits,
and so forth.

3. Under General Protocol Settings, set the Select Serial Port Protocol to Modbus slave.

4. Under Modbus Slave Protocol Settings, set the Device Response Timeout to the desired value.

Note: 2- and 4-Port only: set the Lost Device Search Enable setting. For a discussion on this setting, see

2.4.2.

Modbus Slave Device Search Methodology on Page 30.

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 2. Programming Interface - 29

Modbus Slave Device Search Methodology

5. In the PLC program, address messages to the Modbus slave device using the IP Address of the
DeviceMaster UP and the Unit Identifier of the slave device(s).

2.4.2. Modbus Slave Device Search Methodology

Locating a Modbus slave device on a DeviceMaster UP 1-port is relatively simple. Either the Modbus slave
device is connected to the port or it is not. However, if more than one port is configured for Modbus slave on a
DeviceMaster UP 2- or 4-port, the device must be found. The following is an explanation of how the search
algorithm works on a DeviceMaster UP 2- or 4-port.

Locating a Modbus slave device after a reboot or port reset:

When the DeviceMaster UP receives a message for a Modbus slave device for the first time since reboot or
port initialization, it will transmit the Modbus slave message out all Modbus slave serial ports and wait for a
response to be returned. Once the response is returned, the device port is known and all messages sent to the
device will be routed through the serial port.

Lost Devices:

Lost devices, or devices that time out, are a special case. The DeviceMaster UP provides two methods for
handling lost devices via the Lost Device Search Enable option on the web page.

• Disabling this option on a Modbus slave port:

- Prevents the DeviceMaster UP from searching for a lost device on other Modbus slave ports.

- Prevents lost devices known to have been on other ports from being searched for on this port.

Note: This is the recommended setting whenever it is desired to prevent timeout delays on other Modbus

slave ports in the event that a device times out.

• Enabling this option on a Modbus slave port:

- Allows the DeviceMaster UP to search for lost devices on all Modbus slave ports with the Lost Device

Search Enable option turned on.

Note: This can be useful for locating devices if a device has been moved onto another port by moving

the serial cable or, perhaps, by moving the device onto a different Modbus slave serial loop.

- This will cause timeout delays on all Modbus slave ports with the Device Search Enable option turned

on until the device is found.

30 - Chapter 2. Programming Interface DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I