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ICP DAS USA GW-2500iM Series User Manual

Tiny modbus tcp to rtu/ascii security gateway
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GW-2500iM Series
User Manual
Tiny Modbus TCP to RTU/ASCII Security Gateway
W
ARRANTY
All products manufactured by ICP DAS are warranted against defective materials for a period of
one year from the date of delivery to the original purchaser.
W
ARNING
ICP DAS assumes no liability for damages consequent to the use of this product. ICP DAS reserves
the right to change this manual at any time without notice. The information furnished by ICP DAS
is believed to be accurate and reliable. However, no responsibility is assumed by ICP DAS for its
use, nor for any infringements of patents or other rights of third parties resulting from its use.
C
OPYRIGHT
Copyright © 2024 by ICP DAS. All rights are reserved.
T
RADEMARKS
Names are used for identification purposes only and may be registered trademarks of their
respective companies.
C
U
ONTACT
S
If you have any questions, please feel free to contact us via email at:
service@icpdas.com
Ver. 1.0, March 2025

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Summary of Contents for ICP DAS USA GW-2500iM Series

  • Page 1 GW-2500iM Series User Manual Tiny Modbus TCP to RTU/ASCII Security Gateway Ver. 1.0, March 2025 ARRANTY All products manufactured by ICP DAS are warranted against defective materials for a period of one year from the date of delivery to the original purchaser.

  • Page 2: Table Of Contents

    PC ....................... - 14 - ONNECTING THE OWER AND ........................- 16 - ONNECTING THE ODBUS EVICES GETTING STARTED FOR GW-2500IM SERIES ON IPV4 ..................- 17 - ........................- 17 - ONFIGURING ETWORK ETTINGS .......................... - 20 - ONFIGURING THE ERIAL ...............................
  • Page 3 GW-2500iM Modbus TCP to RTU/ASCII Gateway ............................... - 34 - ETWORK 5.3.1 IP Address Selection ..........................- 34 - 5.3.2 General Settings ............................- 38 - 5.3.3 Modbus Settings ............................. - 39 - 5.3.4 Restore to factory default states ......................- 40 - ............................
  • Page 4 GW-2500iM Modbus TCP to RTU/ASCII Gateway 05(0x05) Force a Single Coil (Write DO) ........................- 86 - 06(0x06) Preset a Single Register (Write AO) ....................... - 87 - 15(0x0F) Force Multiple Coils (Write DOs) ........................- 88 - 16(0x10) Preset Multiple Registers (Write AOs) ....................- 89 - ............................

  • Page 5: Introduction

    1. Introduction Modbus has become the de facto standard protocol for industrial communication, and is now the most commonly available means of connecting industrial electronic devices. Modbus allows for communication between many devices connected to the same RS-485 network, for example, a system that measures temperature and humidity and communicates the results to a computer.
  • Page 6 GW-2500iM Modbus TCP to RTU/ASCII Gateway In harsh industrial environments, the GW-2500iM series also adds 3000 V and +/- 4 kV ESD protection component that diverts the potentially damaging charge away from sensitive circuit to protects the module and equipment from the sudden and momentary electric current.

  • Page 7: Features

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 1.1 Features  Supports Modbus TCP/UDP master and slave  Supports Modbus RTU/ASCII master and slave  Max. connections (masters) per serial port: 32  Read-cache ensures faster Modbus TCP/UDP response  Supports UDP responder for device discovery (UDP Search) ...

  • Page 8: Applications

    Factory Automation  Building Automation  Home Automation  Remote Diagnosis and Management More Information  Documentation GW-2500iM Series https://www.icpdas.com/en/download/index.php?nation=US&kind1=&model=&kw=GW-2500  Firmware GW-2500iM Series https://www.icpdas.com/en/download/show.php?num=2750  Software eSearch Utility https://www.icpdas.com/en/product/guide+Software+Utility_Driver+eSearch__Utility Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved.

  • Page 9: Web Server Technology

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 1.3 Web Server Technology Web server technology enables the GW-2500iM to be configured via a standard web browser interface, e.g., Google Chrome, Internet Explorer, or Firefox, etc. This means that it is easy to check the configuration of the GW-2500iM via an Ethernet network without needing to install any other software tools, thereby reducing the learning curve required for maintaining the device.

  • Page 10: Hardware Information

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 2. Hardware Information This chapter provides a detailed description of the front panel, the hardware specifications, the pin assignments, the wiring notes and the dimensions for the GW-2500iM series modules. 2.1 Specifications Model GW-2515iM...

  • Page 11: Appearance

    Reset button PoE and Ethernet RJ-45 Jack The GW-2500iM series module is equipped with two RJ-45 jacks that are used as the 10/100 Base-TX Ethernet port and features networking capabilities, only ETH1 supports PoE power supply. When an Ethernet link is detected and an Ethernet packet is received, the Link/Act LED (Orange) indicator will be illuminated.

  • Page 12: Reset Button

    GW-2500iM Modbus TCP to RTU/ASCII Gateway Reset button It can help you to upload the firmware in rescue mode when your GW-2500iM fails to recovery/update firmware in a normal way. There are 6 recovery processes as shown below: 1) Turn off the Power. 2) Keep pressing the reset button then turn on the power.

  • Page 13: Led Indicator

    Clicking “Search Server” on eSearch Utility again, you will see the module name as a “GW-2515i”. LED Indicator Once power is supplied to the GW-2500iM series module, the system LED indicator will illuminate. An overview of the system LED functions is given below:...

  • Page 14: Din-Rail Mounting

    GW-2500iM Modbus TCP to RTU/ASCII Gateway DIN-Rail Mounting The GW-2500iM series modules include simple rail clips on the bottom of the chassis that allow them to be reliably mounted on a DIN-Rail or a wall. For more detailed information regarding DIN-Rail Mounting, refer to the illustration in figure below.

  • Page 15: Dimensions

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 2.3 Dimensions The following diagrams provide the dimensions of the GW-2500iM series module. All dimensions are in millimeters.  GW-2515/2535iM (Unit: mm) GW-2515iM 1 port GW-2535iM 3 ports Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved.

  • Page 16: Pin Assignments

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 2.4 Pin Assignments GW-2515iM GW-2535iM Terminal No. Pin Assignment ISO.GND RxD3- COM3 RxD3+ TxD3-/D3- TxD3+/D3+ ISO.GND RxD2- COM2 RxD2+ TxD2-/D2- TxD2+/D2+ ISO.GND ISO.GND RxD1- RxD1- COM1 RxD1+ RxD1+ TxD1-/D1- TxD1-/D1- TxD1+/D1+ TxD1+/D1+ Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved. - 12 -...

  • Page 17: Wiring Notes For Rs-485/422 Interfaces

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 2.5 Wiring Notes for RS-485/422 Interfaces RS-422 Wiring RS-485 Wiring Notes: 1. Usually, you have to connect all signal grounds of RS-422/485 devices together to reduce common-mode voltage between devices. 2. Twisted-pair cable must be used for the D+/- wires. 3.

  • Page 18: Connecting The Power And Host Pc

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 2.6 Connecting the Power and Host PC 1. Ensure that the network settings on your PC are configured correctly. 2. Ensure that the Windows firewall or any Anti-Virus firewall software is correctly configured or temporarily disable these functions;...
  • Page 19 GW-2500iM Modbus TCP to RTU/ASCII Gateway +12 to +48 V Jack Power Supply (Non-PoE) 4. Verify that the System (Sys.) LED indicator is flashing. Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved. - 15 -...

  • Page 20: Connecting The Modbus Devices

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 2.7 Connecting the Modbus Devices Note: The wiring and supply power method vary depending on your Modbus device. Here, the M-7022 module is used as an example. For other Modbus device or third party Modbus device, refer to the product user manual for relevant information.

  • Page 21: Getting Started For Gw-2500Im Series On Ipv4

    IPv4 This chapter provides detailed information about the “Self-Test” process, which is used to confirm that the GW-2500iM series module is operating correctly. Before beginning the “Self-Test” process, the wiring test, Ethernet configuration and search/Modbus utility driver installation procedures must first be fully completed. Follow the procedure described below: Note: This chapter is based on IPv4 environment.
  • Page 22 GW-2500iM Modbus TCP to RTU/ASCII Gateway Factory Default Settings of GW-2500iM Series Module: IPv4 settings Writable  IP Address 192.168.255.1  Subnet Mask 255.255.0.0  Gateway 192.168.0.1 IPv6 settings Writable  User-defined fc00::1  Link-Local EUI-64 format  SLAAC Auto-Configure 5.
  • Page 23 GW-2500iM Modbus TCP to RTU/ASCII Gateway 6. Wait 2 seconds and click “Search Servers” button again to ensure the GW-2500iM is working well with new configuration. Click the “Web” button to log in to the web configuration pages. (Or enter the URL address of the GW-2500iM in the address bar of the browser.) ...

  • Page 24: Configuring The Serial Port

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 3.2 Configuring the Serial Port 1. Open a web browser, such as Google Chrome, Internet Explorer, or Firefox, enter the IP address of the GW-2500iM module in the address bar and then click “Enter”, or click the “Web” button in the eSearch Utility.
  • Page 25 GW-2500iM Modbus TCP to RTU/ASCII Gateway 4. Click the “Port1” tab to display the Port1 Settings page. Select the appropriate Baud Rate, Data Format and Modbus Protocol (e.g., 19200, 8N2 and Modbus RTU) from the relevant drop down options. Notes: 1.
  • Page 26 GW-2500iM Modbus TCP to RTU/ASCII Gateway 5. Click “Submit” to save your settings. Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved. - 22 -...

  • Page 27: Self-Test

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 3.3 Self-Test 1. In the eSearch Utility, select the “Modbus TCP Master” item from the “Tools” menu to open the Modbus TCP Master Utility.  2. In the Modbus TCP Master Utility, enter the IP address of GW-2500iM in the “Modbus TCP” section, and then click the “Connect”...

  • Page 28: Getting Started For Gw-2500 Series On Ipv6

    IPv6 This chapter provides detailed information about the “Self-Test” process, which is used to confirm that the GW-2500iM series module is operating correctly. Before beginning the “Self-Test” process, the wiring test, Ethernet configuration and search/Modbus utility driver installation procedures must first be fully completed. Follow the procedure described below: Note: This chapter is based on IPv6 environment.
  • Page 29 GW-2500iM Modbus TCP to RTU/ASCII Gateway 4. Every IPv6 device has the Link-Local address. You can view the Link-Local address of the GW-2500iM module in the “Link-Local” field without configuring. If your environment supports Stateless Address Auto-configuration (SLAAC), the SLAAC field will display the SLAAC address when the SLAAC configuration is completed.

  • Page 30: Configuring The Serial Port

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 4.2 Configuring the Serial Port 1. Right Click on the Link-Local field and click the “Copy to Clipboard” to copy the “Link-Local address” of the GW-2500iM module. 2. Paste the “Link-Local address” of the GW-2500iM module in the address bar of the browser and add the brackets, i.e., [Link-Local address].
  • Page 31 GW-2500iM Modbus TCP to RTU/ASCII Gateway 3. To enhance the security, you are prompted to change the password when you login to the module for the first time. 4. Go to the “Password” setting, user can modify the default password: Admin in the Current password field.
  • Page 32 GW-2500iM Modbus TCP to RTU/ASCII Gateway Select the appropriate Baud Rate, Data Format and Modbus Protocol (e.g., 19200, 8N2 and Modbus RTU) from the relevant drop down options.  Notes: 1. The Baud Rate, Data Format and Modbus protocol settings depends on your Modbus device. 2.

  • Page 33: Self-Test

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 4.3 Self-Test 1. Download and install the “Modbus Poll” test program at below link. https://www.modbustools.com/download.html  2. Double-click the Modbus Poll shortcut to open. 3. Select the “Read/Write Definition…” item from the “Setup” menu to open the “Read/Write Definition”...
  • Page 34 GW-2500iM Modbus TCP to RTU/ASCII Gateway 5. Select the “Connect…” item from the “Connection” menu to open the “Connection Setup” dialog box. 6. Configure the IPv6 address and TCP port (default: 502) of GW-2500iM and click “OK” to connect the GW-2500iM for testing. ...

  • Page 35: Web Configuration

    Utility described above, or via a standard web browser. 5.1 Logging in to the GW-2500iM Web Server The embedded GW-2500iM series web server can be accessed from any computer that has an Internet connection. 1: O...
  • Page 36 GW-2500iM Modbus TCP to RTU/ASCII Gateway 3: E NTER THE ASSWORD After connecting to the IP address, the login page is displayed. Enter your password in the Login password field, and then click the “Sign in” button to continue. (If this is the first time you login, refer to Section 3.4 to change the factory default password.)

  • Page 37: Home Page

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.2 Home Page The Home link connects to the main page, which contains two parts. The first part of this page provides basic information about the GW-2500iM hardware and software. The software and hardware information section includes information related to the Model Name, the current Firmware version, the IP Address, the current position of the Initial Switch, the Alias, the MAC Address, and the TCP Port, and the System Timeout values.

  • Page 38: Network Page

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.3 Network Page After clicking the Network tab, the Network page will be displayed, allowing you to verify the current settings, configure the IP Address, and the general parameters, and restore the default settings for the GW-2500iM module, each of which will be described in more detail below. 5.3.1 IP Address Selection The Address Type, Static IPv4 Address, Subnet Mask and Default Gateway values are the most important network settings and should always correspond to the LAN configuration.
  • Page 39 GW-2500iM Modbus TCP to RTU/ASCII Gateway The following is an overview of the parameters contained in the IP Address Selection section: Item Description Static IP: If no DHCP server is installed on the network, the network settings can be configured manually. Refer to Section “Manual Configuration”...
  • Page 40 GW-2500iM Modbus TCP to RTU/ASCII Gateway Manual Configuration When using manual configuration, the network settings should be assigned in the following manner: Step 1: Select the “Static IP” option from the “Address Type” drop-down menu. Step 2: Enter the relevant details in the respective network settings fields. If your environment doesn’t support the IPv6, please ignore the “IPv6 User-defined Address”...
  • Page 41 GW-2500iM Modbus TCP to RTU/ASCII Gateway Dynamic Configuration Dynamic configuration is very easy to perform. If a DHCP server is connected to you network, an IPv4 network address can be dynamically configured by using the following procedure: Step 1: Select the “DHCP” option from the “Address Type” drop-down menu. Step 2: Click the “Update Settings”...

  • Page 42: General Settings

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.3.2 General Settings The following is an overview of the parameters contained in the General Settings section: Item Description Default This parameter is used to set the Ethernet speed. The default value is Ethernet Speed Auto Auto (Auto = 10/100 Mbps Auto-negotiation).

  • Page 43: Modbus Settings

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.3.3 Modbus Settings The following is an overview of the parameters contained in the Modbus Settings section: Item Description Default Gateway Net ID This is reserved for gateway. (Not used to set the slave device) This parameter is used to enable or disable whether the slave response is checked for compatibility with the Modbus RTU format.

  • Page 44: Restore To Factory Default States

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.3.4 Restore to factory default states Use the following procedure to reset all parameters to their original factory default settings: Step 1: Click the “Restore Defaults” button to reset the configuration. Step 2: Click the “OK” button in the message dialog box. The following is an overview of the factory default settings: IPv4 Network Settings IPv6 Network Settings...
  • Page 45 GW-2500iM Modbus TCP to RTU/ASCII Gateway Step 3: Check whether the module has been reset to the original factory default settings for use with the eSearch Utility. Refer to Chapter 3 “Getting Started for GW-2500iM series using IPv4”, Chapter 4 “Getting Started for GW-2500iM series using IPv6”...

  • Page 46: Serial Port Page

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.4 Serial Port Page After clicking the Port1 tab, the serial port settings page will be displayed, allowing you to configure the settings for the GW-2500iM, including the Baud Rate, Data Format, Slave Timeout, Char Timeout, Silent Time, Read Cache, TCP Timeout, Modbus Protocol and Pair-connection parameters, etc., each of which will be described in more detail below.
  • Page 47 GW-2500iM Modbus TCP to RTU/ASCII Gateway The following is an overview of the parameters contained in the Settings– Port1 Settings section: Item Description Default Port Settings Baud Rate (bps) This parameter is used to set the Baud Rate for the COM ports. 115200 Data Size (bits) This parameter is used to set the Data Size for the COM ports.

  • Page 48: Pair-Connection Settings

    GW-2500iM Modbus TCP to RTU/ASCII Gateway Item Description Default Modbus TCP Settings When sharing Modbus RTU/ASCII device/data between several master Read Cache devices, the read-cache function can be used to reduce the loading on the serial communication and ensure faster TCP responses. (ms) Valid range: 10, 20to 65530 (ms);...

  • Page 49: Filter Page

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.5 Filter Page The Filter page is used to query or edit the IP Filter List. The IP Filter List restricts the access of packets based on the IP header. If the filter function is enabled, only clients whose IP is specified in the IP Filter List can access the GW-2500iM.

  • Page 50: Snmp Page

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.6 SNMP Page The GW-2500iM series module supports the standard SNMP v3c protocol. Through this protocol, the GW-2500iM series module can transmit modules information to the SNMP Network Management Software or device to help administrators to monitor the status of the modules in real-time.

  • Page 51: Snmp Configuration Setting

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.6.1 SNMP Configuration Setting The following is an overview of the parameters contained in the System Info section: Item Description Default Value User Contact The module contact person Location The module location Site Modbus Description The description of the module Gateway...

  • Page 52: Snmp I/O Example

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.6.2 SNMP I/O Example This article takes iReasoning MIB Browser V14 as an example (hereinafter referred to as MIB Browser). Please download the installer program from its official website and run the installer. http://www.ireasoning.com/mibbrowser.shtml Step 1: Start the MIB Browser.
  • Page 53 GW-2500iM Modbus TCP to RTU/ASCII Gateway Step 2: Enter the IP address of the GW-2500iM module in the Address field. Step 3: Click “Advanced” to set the parameters of the SNMP agent. Enter the string in the Read/Write Community fields according to the Read-Only Community / Read-Write Community settings on the GW-2500iM.
  • Page 54 GW-2500iM Modbus TCP to RTU/ASCII Gateway Step 4: Enter the IP address of MIB Browser in the Manager/Trap IP #1 field, check the Check to enable checkbox to enable the SNMP function, then click” Update Settings” to save the changes. Finally, click the “Reboot” button to reboot the GW-2500iM module. ...

  • Page 55: Snmp Trap Example

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.6.3 SNMP Trap Example Step 1: Click Tools => Trap Receiver on the menu bar to display the window for receiving the Trap messages. Step 2: The Trap types for the alarms that receive from the GW-2500iM module are as follows. 1.

  • Page 56: Snmp Troubleshooting

    GW-2500iM Modbus TCP to RTU/ASCII Gateway Item Description Source The IP address of the Trap from the module. Timestamp The time elapsed since the last startup of the module. SNMP Version The version of SNMP Enterprise The name of the enterprise SNMP community name according to the Trap Community setting on the Community GW-2500iM...
  • Page 57 GW-2500iM Modbus TCP to RTU/ASCII Gateway Step 1: Enter services.msc in the command bar and click to open the Windows service tool.   Step 2: Double-click the SNMP Trap and confirm the Startup type is set to “Disabled” and the Service status is set to “Stopped”.

  • Page 58: Smtp Page

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.7 SMTP Page SMTP is a typical client-server protocol. This SMTP client allows you to quickly send email messages through an SMTP server. This application also supports message attachments and SSL for secure connections. Copyright ©...

  • Page 59: Maintenance Page

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.8 Maintenance Page The Maintenance Page allows you to quickly setup Time server setting, Firmware update, Time-Sensitive, networking and IEEE 802.1X Authentication. 5.8.1 Time Server Settings 5.8.2 Advanced Setting Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved. - 55 -...

  • Page 60: Firmware Update

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.8.3 Firmware Update Firmware update requires initialization and local network operations. Traditional firmware update requires adjusting the Reset button and reboots the module manually for the initialization of firmware update, while new way allows user to initialize the module via web interface without adjusting the hardware switch.
  • Page 61 GW-2500iM Modbus TCP to RTU/ASCII Gateway For detailed information regarding how to use this function to update the Firmware for GW-2500iM series module, refer to the “GW-2500iM Firmware Update Manual (EN)”. The download address is shown below: GW-2500iM : https://www.icpdas.com/en/download/show.php?num=2750 Copyright ©...

  • Page 62: Time-Sensitive Networking

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.8.4 Time-Sensitive Networking 5.8.5 Backup and Authentication certificate Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved. - 58 -...

  • Page 63: Ieee 802.1X Authentication

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.8.6 IEEE 802.1X Authentication Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved. - 59 -...

  • Page 64: Monitor Page

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.9 Monitor Page After clicking the Monitor tab, the Current Connection Status page will be displayed showing detailed information regarding the current status of the serial port connection settings for the GW-2500iM. Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved. - 60 -...

  • Page 65: Netstat Page

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.10 Netstat Page Netstat is a handy tool that can help you understand and troubleshoot your network, as well as detect and resolve network security issues. Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved. - 61 -...

  • Page 66: Password Page

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.11 Password Page After clicking the Password tab, the Privilege Management page will be displayed. Follow the steps below to reset or create a new your account and password. Step 1: Enter the account and password in the field. (Use the default password “Admin” for the first login) Step 2: Enter the new password in the “Confirm new password”...

  • Page 67: Logout Page

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 5.12 Logout Page After clicking the Logout tab, you will be immediately logged out from the system and be returned to the login page. Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved. - 63 -...

  • Page 68: Typical Applications

    Client Mode, etc... 6.1 Modbus Gateway The GW-2500iM series module is a Modbus TCP/UDP to RTU/ASCII gateway that enables a Modbus TCP/UDP host to communicate with serial Modbus RTU/ASCII devices through an Ethernet network, and eliminates the inherent cable length limitations of legacy serial communication devices.

  • Page 69: Modbus Net Id

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 6.2 Modbus Net ID The GW-2500iM series module is a gateway that can be used to convert between the Modbus TCP/UDP protocol and the Modbus RTU/ASCII protocol. Consequently, SCADA/HMI applications is able to access each Modbus RTU/ASCII slave device via the GW-2500iM gateway by specifying correct Net ID of the intended slave device in each Modbus TCP request.

  • Page 70: Pair-Connection Applications

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 6.3 Pair-connection Applications The GW-2500iM Modbus gateway can be used to create a pair-connection applications (as well as serial-bridge or serial-tunnel), and then route Modbus messages between two serial devices via TCP/IP, which is useful when connecting Modbus RTU/ASCII devices that do not themselves have Ethernet capability.
  • Page 71 Step 1: Connecting to a network, PC and Power 1. Confirm that the GW-2500iM modules are functioning correctly. For detailed information regarding how to install, configure and operate your GW-2500iM series module, refer to Chapter 3 “Getting Started for IPv4”,...
  • Page 72 GW-2500iM Modbus TCP to RTU/ASCII Gateway The image below shows an example of the setup for a pair-connection test: Figure 6-1 Step 2: Configuring the Ethernet Settings Contact your Network Administrator to obtain the correct and functioning network configuration for the GW-2500iM modules (including the IP Address, Mask and Gateway details). Figure 6-2 Copyright ©...
  • Page 73 GW-2500iM Modbus TCP to RTU/ASCII Gateway Step 3: Configuring the Pair-connection (Client Mode) on the Web Server for GW-2515iM #1 1. Open the eSearch Utility to search for the GW-2500iM modules connected to the network. Click the name of the first GW-2500iM module (GW-2515iM #1) to select it, and then click the “Web” button to launch a browser window to connect to the web server on the GW-2515iM #1 module.
  • Page 74 GW-2500iM Modbus TCP to RTU/ASCII Gateway 4. Select the appropriate Baud Rate, Data Format and Modbus Protocol settings from the relevant drop down options. The following is an example: Baud Rate (bps) “115200”, Data Bits (bits) “8”, Parity “None”, Stop Bits (bits) “1” and Modbus Protocol “Modbus RTU”. Figure 6-5 5.
  • Page 75 GW-2500iM Modbus TCP to RTU/ASCII Gateway Step 4: Configuring the Pair-connection (Server Mode) on the Web Server for GW-2535iM #2 1. In the eSearch Utility, click the name of the second GW-2500iM module (GW-2535iM #2) to select it, and then click the “Web” button to launch a browser window to connect to the web server on the GW-2535iM #2 module.
  • Page 76 GW-2500iM Modbus TCP to RTU/ASCII Gateway Step 5: Testing the Pair-connection Functions 1. In the eSearch Utility, select the “Modbus RTU Master” item from the “Tools” menu to open the Modbus TCP Master Utility. Figure 6-8 2. Select the appropriate COM port, Baud Rate and Data Format (e.g., COM1, 115200, N, 8, 1) settings for the GW-2500iM, and then click the “Open”...
  • Page 77 GW-2500iM Modbus TCP to RTU/ASCII Gateway 3. Refer to the "Protocol Description” field in the top right-hand section of the Modbus Utility window. You can send a request command and confirm the response is correct. Step 1: Enter the Modbus command in the “Command” field Step 2: Click the “Send Command”...

  • Page 78: Tcp Client Mode Applications

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 6.4 TCP Client Mode Applications In TCP Client Mode, the GW-2500iM can actively establish a TCP connection to a specific Modbus TCP slave device. An example of how the complete system should operate is shown below: Figure 6-11 The following are examples of pair-connection tests: ...
  • Page 79 Step 1: Connecting to a network, a PC and a Power Supply 1. Confirm that the GW-2500iM device is functioning correctly. For detailed information regarding how to install, configure and operate your GW-2500iM series module, refer to Chapter 3 “Getting Started for GW-2200iM series using IPv4”,...
  • Page 80 GW-2500iM Modbus TCP to RTU/ASCII Gateway Step 2: Configuring the Ethernet Settings Contact your Network Administrator to obtain a correct and functioning network configuration (including the IP Address, Mask and Gateway details) for the GW-2515iM module. Figure 6-13 Step 3: Configuring Pair-connection (TCP Client Mode) on the Web Server for the GW-2500iM module 1.
  • Page 81 GW-2500iM Modbus TCP to RTU/ASCII Gateway 3. Click the “Port1” tab to display the Port1 Settings page. Figure 6-15 4. Select the appropriate Baud Rate, Data Format and Modbus Protocol settings from the relevant drop down options. The following is an example: Baud Rate (bps) “115200”, Data Bits (bits) “8”, Parity “None”, Stop Bits (bits) “1”...
  • Page 82 GW-2500iM Modbus TCP to RTU/ASCII Gateway 5. In the Pair-connection Settings area of the Port1 Settings page, check that the configuration details are the same as those shown below. Application Network Protocol Remote Server IP Remote TCP Port Field Mode TCP / IPv4 10.0.8.10 Pair-Connection...

  • Page 83: Modbus Information

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 7. Modbus Information What is Modbus TCP/IP? Modbus is a communication protocol developed by Modicon in 1979. You can also visit http://www.modbus.org to find more valuable information. The Different versions of Modbus used today include Modbus RTU (based on serial communication interfaces such as RS485 and RS232), Modbus ASCII and Modbus TCP, which is the Modbus RTU protocol embedded into TCP packets.
  • Page 84 GW-2500iM Modbus TCP to RTU/ASCII Gateway Leading 6 bytes of Modbus TCP protocol: Byte 00 Byte 01 Byte 02 Byte 03 Byte 04 Byte 05 Transaction Length field Length field Protocol identifier identifier (upper byte ) (lower byte) Transaction identifier: Assigned by Modbus TCP master (client) Protocol identifier: 0 Length field (upper byte): 0 (since all messages are smaller than 256) Length field (lower byte): Number of following RTU data bytes...
  • Page 85 GW-2500iM Modbus TCP to RTU/ASCII Gateway Code Function Reference (Address) 01 (0x01) Read the Status of the Coils (Readback DOs) 0xxxx 02 (0x02) Read the Status of the Input(Reads DIs) 1xxxx 03 (0x03) Read the Holding Registers (Readback AOs) 4xxxx 04 (0x04) Read the Input Registers (Reads AIs) 3xxxx...

  • Page 86: 0X01) Read The Status Of The Coils (Readback Dos)

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 01(0x01) Read the Status of the Coils (Readback DOs) This function code is used to read either the current status of the coils or the current digital output readback value. [Request] Byte Description Size Value Net ID (Station Number) 1 Byte...

  • Page 87: 0X02) Read The Status Of The Input (Read Dis)

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 02(0x02) Read the Status of the Input (Read DIs) This function code is used to read the current digital input value. [Request] Byte Description Size Value Net ID (Station Number) 1 Byte 1 to 247 Function Code 1 Byte 0x02...

  • Page 88: 0X03) Read The Holding Registers (Readback Aos)

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 03(0x03) Read the Holding Registers (Readback AOs) This function code is used to readback either the current values in the holding registers or the analog output value. [Request] Byte Description Size Value Net ID (Station Number) 1 Byte 1 to 247 Function Code...

  • Page 89: 0X04) Read The Input Registers (Read Ais)

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 04(0x04) Read the Input Registers (Read AIs) This function code is used to read either the input registers or the current analog input value. [Request] Byte Description Size Value Net ID (Station Number) 1 Byte 1 to 247 Function Code 1 Byte...

  • Page 90: 0X05) Force A Single Coil (Write Do)

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 05(0x05) Force a Single Coil (Write DO) This function code is used to set the status of a single coil or a single digital output value. [Request] Byte Description Size Value Net ID (Station Number) 1 Byte 1 to 247 Function Code...

  • Page 91: 0X06) Preset A Single Register (Write Ao)

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 06(0x06) Preset a Single Register (Write AO) This function code is used to set a specific holding register to store the configuration values. [Request] Byte Description Size Value Net ID (Station Number) 1 Byte 1 to 247 Function Code 1 Byte...

  • Page 92: 0X0F) Force Multiple Coils (Write Dos)

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 15(0x0F) Force Multiple Coils (Write DOs) This function code is used to set multiple coils status or write multiple digital output values. [Request] Byte Description Size Value Net ID (Station Number) 1 Byte 1 to 247 Function Code 1 Byte 0x0F...

  • Page 93: 0X10) Preset Multiple Registers (Write Aos)

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 16(0x10) Preset Multiple Registers (Write AOs) This function code is used to set multiple holding registers that are used to store the configuration values. [Request] Byte Description Size Value Net ID (Station Number) 1 Byte 1 to 247 Function Code 1 Byte...

  • Page 94: Exception Codes

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 7.2 Exception Codes If an exception occurs during Modbus communication, the slave device will return an Exception Code in the response message. The following is an explanation of the Exception Codes:  Exception Codes: Code Name and Description ILLEGAL FUNCTION...
  • Page 95 GW-2500iM Modbus TCP to RTU/ASCII Gateway  Defined Exception Codes for GW-2500iM: Code Name and Description GATEWAY TARGET DEVICE FAILED TO RESPOND 0x0B Timeout. The slave device does not respond within the timeout value, the GW-2500iM will return this code. GATEWAY TARGET DATA FAILED TO RESPOND 0x4B Timeout.

  • Page 96: Appendix A: Glossary

    GW-2500iM Modbus TCP to RTU/ASCII Gateway Appendix A: Glossary 1. ARP (Address Resolution Protocol) The Address Resolution Protocol (ARP) is a telecommunication protocol that is used to convert an IP address to a physical address, such as an Ethernet address. Consider two machines A and B that share the same physical network.

  • Page 97: Ethernet

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 3. Ethernet The term Ethernet generally refers to a standard published in 1982 by Digital Equipment Corp., Intel Corp. and Xerox Corp. Ethernet is the most popular physical layer Local Area Network (LAN) technology in use today. 4.

  • Page 98: Ip (Internet Protocol) Address

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 8. IP (Internet Protocol) Address Each interface on the Internet must have a unique IP address (also called an Internet address). These addresses are 32-bit numbers, and are normally written as four decimal numbers, one for each byte of the address for example “192.168.41.1”.

  • Page 99: Socket

    GW-2500iM Modbus TCP to RTU/ASCII Gateway 13. Socket Each TCP segment contains a source and destination port number that can be used to identify the sending and receiving application. These two values, along with the source and destination IP addresses in the IP header, uniquely identify each connection. The combination of an IP address and a port number is called a socket.

  • Page 100: Appendix B: Actual Baud Rate Measurement

    GW-2500iM Modbus TCP to RTU/ASCII Gateway Appendix B: Actual Baud Rate Measurement Ideal Baud Rate (bps) Actual Baud Rate (bps) Error 298.48 0.51% 597.04 0.49% 1200 1197.6 0.20% 2400 2395.2 0.20% 4800 4790.4 0.20% 9600 9568.0 0.33% 14400 14392 0.05% 19200 19136 0.33%...

  • Page 101: Appendix C: Revision History

    GW-2500iM Modbus TCP to RTU/ASCII Gateway Appendix C: Revision History This chapter provides revision history information to this document. The table below shows the revision history. Revision Date Description March 2025 Initial issue Copyright © 2025 ICP DAS CO., Ltd. All Rights Reserved. - 97 -...

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