Document Version: V1.0

Gateways & Firmware Requirement:

1. Manual Description

1.1 Manual Purpose

This manual guides field technicians to quickly configure the Robustel edge computing gateway to forward collected data from LoRa devices to higher-level systems (such as SCADA, MES, or upper computer software) using the Northbound Modbus TCP Slave protocol.

1.2 Scope of Application

This manual is written for field implementation engineers. You do not need deep theoretical knowledge of the Modbus protocol. By following these step-by-step instructions, you can easily configure the gateway as a Modbus TCP Slave, map internal data tags to Modbus registers, and verify the data using third-party tools.

2. Basic Concepts & Network Topology

Gateway Role: From Collector to Server

In a typical IIoT project, imagine the gateway as a translator between your local sensors and the upper-level system. The data flow consists of two main stages:

First Stage (Southbound): The field LoRa sensors communicate with the gateway wirelessly using radio frequencies. The gateway acts as a LoRaWAN Network Server (LNS), receiving raw data sent by the sensors and parsing/decoding it, then storing the values internally as Tags.

Second Stage (Northbound): The gateway operates as a Modbus TCP Slave on the network. It takes those internal Tags, converts them into standard Modbus register addresses, and exposes them so that a higher-level system, such as SCADA, MES, or a Modbus testing tool like Modbus Slave, can continuously read the values.

3. Preparations

(Note: This document uses the LG3120e gateway and E2C Field software as an example. The configuration process for other supported gateway and software combinations is very similar.)

Before starting the configuration, please ensure the following preparations are met:

3.1 Hardware Device Requirements

3.2 Environment and Network Requirements

• LAN Connectivity: The gateway and the debugging PC must be connected to the same Local Area Network (LAN) (e.g., connected to the same switch or the gateway's LAN ports). LoRa sensors communicate with the gateway wirelessly via radio frequencies and do not require an Ethernet cable.
• IP Allocation: Ensure all devices requiring IP addresses have valid IP addresses in the same subnet (e.g., 192.168.0.x) and there are no IP conflicts.
• Port Accessibility: Ensure the PC's firewall allows TCP traffic on the Modbus TCP port you configured (default 502).
• Modbus Testing Tool: Download and install Modbus Slave on your debugging PC. It is a free, industry-standard tool used to search and verify Modbus TCP Slave data.

4. Prerequisite: Southbound Data Collection

Before forwarding data via Modbus, the gateway must first collect data from the field devices. In this guide, we will use a LoRaWAN temperature and humidity sensor as an example to collect two tags: Temperature and Humidity.

4.1 Logging into E2C Field

1. Connect your PC to the gateway's LAN port.
2. Open a web browser and enter the gateway's IP address (the default is usually 192.168.0.1).
3. Log in with your credentials and click【Edge Computing】 in the gateway's Web GUI to enter the E2C Field interface.
4. Workflow Overview To set up a new sensor, you need to complete the following steps:
   1. Check if the codec is pre-integrated (Step 1).
   2. If not pre-integrated, obtain and import the codec (Step 2).
   3. Create a Device Profile (Step 3).
   4. Add the LoRaWAN device and associate tags (Step 4).

4.2 Step 1: Check for Payload Codecs

The purpose of this step is to provide the gateway with a "translator" script to convert raw hexadecimal data sent by the sensor into readable data points (e.g., temperature, humidity, or battery level). You only need to do this once per sensor model. Please follow the path below based on your sensor's current status:

Please navigate to LNS Configuration > 【Payload Codecs】.

• If your sensor model is listed, the codec is already built into the system; please proceed directly to 【4.4 Step 3】.
• If your sensor is not listed, please proceed directly to 【4.3 Step 2】.

4.3 Step 2: Importing a Payload Codec

The system supports creating custom Codec files through either Add or Copy methods. These operations require the operator to have a technical background in Codec development. This step explains the method of importing a file, which has a lower barrier to entry and broader applicability, to complete the creation of a Payload Codec for the vast majority of standard use cases.

1. Obtain the Raw Codec File:
   1. Primary Source: Contact the sensor manufacturer directly to obtain the raw Codec file compatible with your specific model.
   2. Public Resources: If the manufacturer does not provide the file directly, you may search for it in these common community repositories:
      - Milesight: https://github.com/Milesight-IoT/SensorDecoders
      - Dragino: https://github.com/dragino/dragino-end-node-decoder
      - Other vendors: https://github.com/TheThingsNetwork/lorawan-devices
2. Convert Codec File Format: Use the conversion tool to process the raw Codec file into the TOML format supported by E2C Field.
   1. Place the e2c-trinity-codec-converter.exe tool and the extracted raw Codec folder into the same directory.
   2. Run the tool, then select the appropriate 【Vendor】 and 【Model】.
   3. Click 【Generate Codec TOML】 to complete the conversion.

4. Import to E2C Field:
   1. Navigate to 【LNS Configuration】 > 【Payload Codecs】 > 【Import Codec】 > 【Import from file】.
   2. Upload the generated TOML file.
   3. Mandatory Testing (Critical Step): This step verifies the decoding logic and determines which data points are available for your device.
      1. Go to the 【Uplink Test】 tab, input the sample hex payload provided in your sensor’s manual, and click 【Run Decode】.
      2. You must ensure the system successfully outputs the JSON result. Please note that the data points available to your device are entirely dependent on the output of this Run Decode process. For example, if your Codec file theoretically supports 50 data points, but the hex payload only successfully parses 2 points during the test, then the device will only possess those 2 data points after binding to this Profile.
      3. If your sensor supports downlink control, please perform the same test under the 【Downlink Test】 tab.
      4. Once the test is successful, you must click 【Publish】 to save the codec; otherwise, it will not take effect.

4.4 Step 3: Create a Device Profile

Purpose of this step: To define the shared network settings for a specific model of sensor. Instead of typing the frequency and join settings for 100 identical sensors, you create one Profile and apply it to all of them.

1. Go to 【LNS Configuration】>【Device Profiles】>【Create New】.
2. Configure the parameters based on your sensor's manual according to the table below:

3. Click 【Publish】 to finish the profile.

4.5 Step 4: Add a Device and Associate Tags

Purpose of this step: To register the actual, physical sensor to the gateway using its unique IDs, and select which data points (Tags) you want to collect.

1. Go to 【Data Collection】>【LoRaWAN Device】>【Add Device】.
2. Configure the physical device identity:

3. Click 【Next】 to enter Tag Verification.
4. The system will automatically list all available data points (Tags) this sensor can provide (e.g., temperature, humidity, battery). Check the boxes for the tags you need.
5. Click 【Confirm】, then click the 【Publish LoRa】 button at the top right of the screen to apply changes.

4.6 Data Collection Verification

Once added, power on or reboot your physical sensor to force it to join the gateway.

1. Verifying Uplink Data (Reading from Sensor)

• Check Connection: Go to 【Data Collection】>【LoRaWAN Device】. Look at the 【Status】 column. A green icon means the sensor has successfully joined the gateway.
• View Data: Click the 【View Tags】 icon (eye symbol) next to your device.
• Observe the 【Latest Value】 and 【Update Time】 columns. If you see real numbers (e.g., 25.5 for temperature) updating periodically, your sensor is successfully online and sending data.

2. Verifying Downlink Data (Writing to Sensor)

If your sensor supports receiving commands (like turning on a relay or changing report intervals):

• In the Tag list window (View Tags), find a tag with 【Read & Write】 permission.
• Click the 【Modify Tag Value】 icon (paper airplane symbol).
• Enter the new command/value (e.g., "off") and click 【Confirm】.
• Note: Because LoRaWAN sensors sleep to save battery, downlink commands are queued and will be executed the next time the sensor wakes up to communicate.

5. Northbound Configuration: Modbus TCP Slave

This is the core step where we expose our internal tags to the Modbus network.

5.1 Creating the Modbus TCP Slave

1. Go to【Data Forwarding】.
2. Click the【+ Create】 button at the top, select【Modbus TCP Slave】, and click【Save】.
3. You will enter the Modbus TCP Configuration page. Enable Modbus TCP Configuration and configure the Basic Settings:

4. Click 【Submit】 to save the basic settings.

5.2 Mapping Tags to Modbus Registers (Crucial Step)

After completing the basic settings, you need to add a slave and map the tags created during data collection to specific register addresses under this slave.

5.2.1 Mapping Strategy Guide (Read before Configuration)

Before you start mapping, please review the following planning principles:

• Address Continuity: To minimize reads from your SCADA, map tags that are polled together to consecutive register addresses. For example: Temperature → 40001, Humidity → 40002.
• Data Type Footprint: An int16 consumes 1 register. A float32 consumes 2 consecutive registers (e.g., 40001-40002). A string consumes multiple registers by byte. Plan your address space to avoid overlaps.
• Function Code Selection: Most SCADA systems use 03 Holding Register for analog values. 04 Input Register is read-only and suitable for device status. 01/02 are for boolean values.
• Naming Convention: Use meaningful names for slaves and mapping tables (e.g., Slave_SCADA_Room1) for easier maintenance.

5.2.2 Adding a Slave

1. In the "Modbus TCP Slave List" section, click 【Add Slave】.
2. Configure the following parameters:

5.2.3 Adding Mappings

After adding the slave, you need to add tag mappings for this slave. The upper-level system (e.g., Modbus Slave) does not understand internal tag names like "Temperature"; it only recognizes standard Modbus register addresses (e.g., 40001). The system supports two methods: 【Add Mapping】 (single) and 【Batch Add Mapping】 (bulk creation).

Method 1: Add Mapping (Single)

Use this method to map tags one by one.

1. In the row of the newly created slave, click the 【Add】 button on the right.
2. Fill in the mapping parameters according to the table below, then click 【Save】:

Method 2: Batch Add Mapping (Bulk Creation)

Use this method to map multiple tags from the same device at once, saving significant configuration time.

1. In the row of the newly created slave, click the 【Batch Add Mapping】 button.
2. In the pop-up window, configure the following:

3. After selecting the device, the table below will automatically display all tags from that device that match the selected function code. Check the boxes next to the tags you want to map (multiple selection allowed).
4. The system will automatically calculate the 【Mapped Address】 for each selected tag based on the starting address and the data type size. For example, if you select 3 tags starting from address 1, the mapped addresses will display as 40001 ~ 40004 (the exact range depends on the number and data types of the selected tags).
5. Click 【Save】 to complete the batch mapping.

Final Steps

1. Repeat steps 5.2.1 and 5.2.2 to create all required slaves and complete the mapping configuration for all tags you need to forward (e.g., Humidity).
2. All configurations take effect immediately upon saving; no need to click the 【Publish】 button.

6. Verifying Configuration with Modbus Slave

Now, let's test if our gateway is successfully working as a Modbus TCP Slave.

1. Open the Modbus Slave software on your PC.
2. Click 【Connection】>【Connect】 on the menu bar.
3. In the pop-up window, configure the following parameters:
   1. Connection Type: Select 【Modbus TCP/IP】
   2. IP Address: Enter the gateway's IP address (e.g., 192.168.0.1)
   3. Port: Enter 502 (or the port number you configured in Basic Settings)
   4. Click 【OK】
4. Click 【Setup】>【Slave Definition】 on the menu bar, and configure the following parameters:
   1. Slave ID: Enter the slave address you configured (e.g., 1)
   2. Function: Select 03 Holding Register (4x)
   3. Address: Enter 1 (corresponding to mapped address 40001)
   4. Quantity: Enter the number of registers to read (e.g., 1 for Temperature)
   5. Click 【OK】
5. In the Modbus Slave main window, you should see real-time data displayed at address 40001. If the displayed values match the values collected from the southbound LoRa device, your Modbus TCP Slave data forwarding is successful.

6. Testing Write-Back Function (Only for Read & Write points). If a mapped point shows 【Read & Write】 in the Mapping Table, you can use Modbus Slave to write a value to the gateway, and the gateway will write this value back to the corresponding southbound LoRa device.
   
   + In Modbus Slave, locate the register address you want to write to (e.g., 40001).
   
   + Double-click the 【Value】 cell for that address.
   
   + Enter a new value in the pop-up window and click 【OK】.
   
   + Observe whether the value changes. If it updates successfully, the write-back function is working. If the value does not change or reverts to the original value, check:
   1. Whether the point's 【R/W Permission】 is Read & Write (if Read Only, write-back is not supported).
   2. Whether the southbound LoRa device supports write operations.

7. Common Troubleshooting

Debugging Workflow (Check in this order)

1. Network Layer: From your SCADA/upper computer, run ping [gateway IP address] in CMD/Terminal.

• Fails? Check cable connections, IP address configuration, and whether your firewall allows the Modbus TCP port you configured.

2. Service Layer: Use the Modbus Slave software to try connecting to the gateway.

• Timeout? Check whether the Modbus TCP Slave Configuration switch on the gateway is enabled and whether the port number matches your configuration (default 502).

3. Data Layer: Connected but reads 0 or error values?

• a. Go back to the gateway Web UI → Data Collection. Check if the Tag you mapped has live, updating values.
• b. If the Tag is fine, check if the Slave ID in your configuration matches the one in Modbus Slave.
• c. Check the Mapped Address: The offset address you configured (e.g., 1) maps to Modbus address 40001. Does the address in Modbus Slave match?