Modbus® Server
User Guide
Trademark Notices
Document Number: 2000535 Rev C
Comtrol, DeviceMaster, and PortVision are registered trademarks of Comtrol Corporation.
Ethernet is a registered trademark of Digital Equipment Corporation, Intel, and Xerox Corporation.
Modbus is a registered trademark of Schneider Electric.
PLC is a registered trademark of Allen-Bradley Company, Inc.
Other product names mentioned herein may be trademarks and/or registered trademarks of their respective
owners.
Third Edition, June 2, 2014
Copyright © 2010 - 2014. 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
Modbus Server Application Overview ..............................................................................5
Recommended Chassis ................................................................................................................................. 5
Terms and Definitions .................................................................................................................................. 6
What is Modbus? ............................................................................................................................................ 6
Modbus/RTU (Supported by Modbus Server)............................................................................................ 6
Modbus/TCP (Not supported by Modbus Server)...................................................................................... 7
Modbus Server Functionality ..................................................................................................................... 7
Other Comtrol Modbus Solutions .............................................................................................................. 9
Modbus Router............................................................................................................................................ 9
Modbus/TCP - Multiple Modbus Master and Slave Types, Serial and Ethernet Raw/ASCII Devices 10
Installation Overview..........................................................................................................11
PortVision DX Overview ............................................................................................................................ 11
Installing PortVision DX............................................................................................................................ 12
Configuring the Network Settings .......................................................................................................... 15
Uploading Modbus Server ......................................................................................................................... 18
Installing the Serial Port Redirector (Optional).................................................................................. 19
Configuring Port Redirector COM Ports ............................................................................................... 21
Adding a Secure Port ................................................................................................................................ 21
Configuring the Secure COM Port........................................................................................................... 22
Embedded Web Pages..........................................................................................................25
Configuration Overview ............................................................................................................................ 25
Server Configuration (Main) Page .......................................................................................................... 26
Serial Interface Configuration Page....................................................................................................... 27
Edit Port Configuration Page................................................................................................................... 28
Edit Network Configuration Page........................................................................................................... 31
Embedded Diagnostic and Statistics Pages ...................................................................33
Known Modbus/RTU Device List Web Page .......................................................................................... 33
Serial Interface Communications Statistics Page ............................................................................... 34
Serial Interface Logs Page ........................................................................................................................ 36
Troubleshooting and Technical Support........................................................................37
Troubleshooting Checklist ....................................................................................................................... 37
General Troubleshooting........................................................................................................................... 38
Daisy-Chaining DeviceMaster 2E/4-Port Units.....................................................................................39
Technical Support ....................................................................................................................................... 40
DeviceMaster UP Modbus Server User Guide: 2000535 Rev. C Table of Contents - iii
TableofContents
iv - Table of Contents DeviceMaster UP Modbus Server User Guide: 2000535 Rev. C
Modbus Server Application Overview
This section defines the software functionality for the Modbus Server application
and provides an overview of other Comtrol Modbus solutions (
The Modbus Server application was designed to provide enhanced connectivity for
O
PC servers and applications that require Modbus/RTU communications. While
standard gateways provide connectivity for only one application per serial port,
Modbus Server provides connectivity for up to six applications per serial port.
Modbus Server was designed to greatly en
Included are comprehensive device and port specific diagnostic web pages that
display status, message response timing, timeout, and other error counts, and
overall message statistics. A serial log is also included to provide message level
diagnosis.
Recommended Chassis
The following table lists the recommended DeviceMaster UP chassis based on
Modbus/RTU message throughput.
Page 9).
hance system maintenance capabilities.
Throughput 1-Port 2-Ports 4-Ports
Very High - Message rate of up to one message every
50 ms per port (20 messages per port per second)
High - Message rate of up to one message every 100
ms per port (10 messages per port per second)
Medium - Message rate of up to one message every
200 ms per port (5 messages per port per second)
Low - Message rate of up to one message every 500 ms
per port (2 messages per port per second)
Very Low - Message rate of up to one message every
second per port (1 message per port per second)
Latency
Transmit (From application to device) 2-10 ms (*)
Receive (From device to application 2-10 ms (*)
(*) = Based on one Ethernet TCP/IP connection per serial port running in a
normal uncongested system. The maximum overall latency will increase as the
number of Ethernet TCP/IP connections increase.
Note: T
hese estimates are based on a Modbus/RTU request and/or response
message size of 20 bytes. Actual throughput will vary depending on message
size and system requirements.
XX
XX X
XX X
XX X
XX X
DeviceMaster Modbus Server User Guide: 2000535 Rev. C Modbus Server Application Overview - 5
Terms and Definitions
Terms and Definitions
This table provides Modbus Server definitions.
Term Definition
What is Modbus?
Master (or Client) Mode
Slave (or Server)
Modbus/RTU
Polling
Sockets
DeviceMaster DeviceMaster RTS or DeviceMaster UP.
The method of operation when a DeviceMaster or an
application is operating as a Master or the message
originator.
The method of operation when a DeviceMaster or an
application is operating as a Slave or the message
receiver.
The standard Modbus messages, in hexadecimal
format, that are typically transmitted over serial lines
but can also be transmitted over other communication
methods such as wireless or Ethernet TCP/IP socket
connections.
Note: Modbus/RTU over Ethernet TCP/IP is not the
same as Modbus/TCP.
The process where an application requests data on a
continual basis. In this operation the Master sends the
request messages while the Slave responds to the
messages.
The method used to communicate between devices
while communicating over Ethernet TCP/IP.
Modbus/RTU (Supported by Modbus Server)
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
• The terms Slave or Server are used to identify the devices responding to the
message.
Modbus/RTU is us
• Serial port connectivity. RS-485 is th
are also used.
• Ethernet TCP/IP socket connections. This is not the same as Modbus/TCP
(please see next section), 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 is not used by PLCs.
ed for:
identify the sender of the message.
e most common, but RS-232 and RS-422
6 - Modbus Server Application Overview DeviceMaster Modbus Server User Guide: 2000535 Rev. C
Modbus/TCP (Not supported by Modbus Server)
Modbus/TCP (Not
supported by Modbus
Server)
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 advanc
ed Ethernet based devices, such as
PLCs, HMIs, SCADA Systems, and most OPC Servers to:
• Other Ethernet devices supporting Modbus/TCP.
• Remote serial Modbus/RTU devices through gateways (such as the
DeviceMaster UP).
• Remote serial or Ethernet TCP/IP ASCII devices through a gateway (such as
the DeviceMaster UP).
Note: Refer to the DeviceMaster UP for Modbus/TCP functionality.
Modbus Server Functionality
The Modbus Server application provides the following functionality:
• Supports Modbus/RTU over Ethernet TCP/IP connections to the
corresponding serial port through intelligent Modbus message handling and
routing.
• Supports only Modbus/RTU over Ethernet TCP/IP connections to a serial port.
Note: For Modbus/TCP functionality, refer the DeviceMaster UP
• Supports up to six Ethernet TCP/IP connections to each serial port.
- One TCP/IP connection can be created with the Connect To connection
method.
-The Listen connection method accepts up to five or six connections,
depending if the Connect To connection is active.
• Supports up to 255 Modbus devices per port. Both valid, (1-247), and reserved,
(248-255), device Ids are supported.
• Modbus/RTU specific message handling:
- CRC verification of all messages received on the TCP/IP and serial
interfaces.
- Timing out of responses from slave Modbus/RTU devices.
- Broadcast message handling on connected port only.
.
DeviceMaster Modbus Server User Guide: 2000535 Rev. C Modbus Server Application Overview - 7
Modbus Server Functionality
• System monitoring to ensure gateway operation:
- Gateway busy.
- Application message time-outs.
• Advanced diagnostics web pages:
- Modbus/RTU device specific statistics and status. Up to 255 Modbus/RTU
devices per port can be monitored simultaneously.
- Serial port specific statistics, response timing, and status.
- Serial port message logging.
• Combined with a serial port redirector, such as the Comtrol Secure Port
Redirector, which can support up to six COM port connections to each serial
port.
8 - Modbus Server Application Overview DeviceMaster Modbus Server User Guide: 2000535 Rev. C
Other Comtrol Modbus Solutions
Comtrol provides several other Modbus solutions other than Modbus Server that
include:
• Modbus Router
•
Modbus/TCP
Other Comtrol Modbus Solutions
Modbus Router Modbus Router firmware was developed to prov
Modbus connectivity from a wide variety of Modbus masters to a wide variety of
local and remote Modbus slaves. Advanced features include master-to-master
communication, private serial bus connectivity, write protection, and device ID
aliasing. With simplified configuration pages and advanced routing, Modbus
Router provides unmatched Modbus connectivity.
ide innovative network-wide
Modbus Router firmware supports the
following controllers:
• Modbus/TCP masters
•
Modbus/RTU and Modbus/ASCII serial masters
• Modbus/RTU and Modbus/ASCII over Ethernet TCP/IP masters
• Modbus Router firmware supports the following devices:
• Modbus/TCP slaves
• Modbus/RTU and Modbus/ASCII serial slaves
With additional gateways, both remote Modbus serial slaves and raw/ASCII
devic
es Modbus Router firmware is recommended in installations that require:
• Local (directly attached) Modbus master
and/or slave connectivity
• No local raw/ASCII device connectivity
• Automatic Modbus protocol translations (if needed)
• Connectivity to remote Modbus slave(s) and/or raw/ASCII device(s)
• Connecting single or multiple Modbus masters to the slave device(s)
DeviceMaster Modbus Server User Guide: 2000535 Rev. C Modbus Server Application Overview - 9
Modbus/TCP - Multiple Modbus Master and Slave Types, Serial and Ethernet Raw/ASCII Devices
• Master-to-Master connectivity (via Shared Memory subsystem)
• Isolation of serial Modbus slaves (via Private Serial Bus connectivity)
• Write protection of serial Modbus slaves
• Modbus Device ID conflict resolution
Modbus/TCP Multiple Modbus
Master and Slave
Types, Serial and
Ethernet Raw/ASCII
Devices
The Modbus/TCP firmware has been designed to provide great flexibility for
connecting both Modbus serial slaves and raw/ASCII devices to a variety of
Modbus controllers and applications.
Such advanced raw/ASCII options as filtering
, command/response mode, peer-topeer Modbus communications and simultaneous connections to multiple Modbus
controllers and/or Ethernet TCP/IP applications make the Modbus/TCP firmware
the flagship of all Modbus to raw/ASCII gateways.
Modbus/TCP firmware supports the
following controllers:
• Modbus/TCP masters and slaves
•
Modbus/RTU and Modbus/ASCII serial masters and slaves
• Applications over Ethernet TCP/IP connections (raw/ASCII only)
Modbus/TCP firmware supports the following devices:
• Raw/ASCII devices, both serial and Ethernet T
CP/IP, such as barcode
scanners, vision systems, RFID readers, weigh scales, encoders and printers
• Modbus/RTU and Modbus/ASCII serial slaves
• Modbus/TCP firmware is recommended in installations that require:
• Connectivity to serial and/or Ethernet TCP/IP raw/ASCII devices
• Connectivity to Modbus/RTU and/or Modbus/ASCII serial devices
• Connectivity from single or multiple Modbus masters and/or applications to
the devices
• Automatic Modbus protocol translations (if needed)
10 - Modbus Server Application Overview DeviceMaster Modbus Server User Guide: 2000535 Rev. C
Installation Overview
Hardware Installation
Documents
Web
DeviceMaster UP Installation and
Configuration Guide
DeviceMaster UP Hardware
Installation and Configuration
Use this section to locate software and installation documentation for the
DeviceMaster UP to quickly install and configure Modbus Server.
An installation follow
1. Connect the DeviceMaster UP to
the network.
If necessary, use the appropriate
hardware installation document
for your DeviceMaster UP.
2. Install PortVision DX. You can
refer to the PortVision DX
Overview subsection to locate
PortVision DX and install it
easily.
3. Configure the DeviceMaster UP network settings using PortVision DX
(Configuring the Network Settings
4. You must upload the Modbus Server firmware into the DeviceMaster UP
using PortVision DX (Uploading Modbus Server
5. Configure the port characteristics using the DeviceMaster UP embedded web
page (Embedded Web Pages
6. Optionally, install the secure COM port redirector if you require COM port
support (Installing the Serial Port Redirector (Optional)
7. Connect any serial device or devices using the appropriate hardware
installation document for your DeviceMaster UP (table, above).
s these basic steps.
on Page 15).
on Page 18).
on Page 25).
on Page 19).
PortVision DX Overview
Use PortVision DX to identify, configure, update, and manage the DeviceMaster
UP on the following operating systems:
• Windows XP
•
Windows Server 2003
• Windows Vista
• Windows Server 2008
• Windows 7
• Windows Server 2012
• Windows 8/8.1
PortVision DX requires that you connect
to the same network segment as the Windows host system if you want to be able to
scan and locate it automatically during the configuration process.
Before installing PortVision DX, consider the following:
• Use PortVision DX to upload firmware and apply changes to a DeviceMaster
that is on the same local network segment as the system on which PortVision
DX is installed. You cannot apply changes through PortVision DX to a
DeviceMaster that is not on the same local network segment.
the Comtrol Ethernet-attached product
DeviceMaster UP Modbus Server User Guide: 2000535 Rev. C Installation Overview - 11
Installation Overview
• Use PortVision DX to monitor any DeviceMaster on the network. The
DeviceMaster does not have to be on the same local network segment as
PortVision DX for monitoring purposes.
Installing PortVision DX
PortVision DX requires that you connect the DeviceMaster UP to the same
network segment as the Windows system during the configuration process.
1. If necessary, download the latest version of PortVision DX from
ftp://ftp.comtrol.com/dev_mstr/portvision_dx/
2. Execute the PortVision_DX_[version].msi file.
3. Click Next on the Welcome screen.
.
4. Click I accept the terms in the License Agreement and Next.
12 - Installation Overview DeviceMaster UP Modbus Server User Guide: 2000535 Rev. C
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