Configure Modbus RTU data collection | Robustel

How to configure Modbus RTU data collection

1. Protocol Overview

  • Protocol Description: Modbus RTU is a standard industrial automation protocol that transmits binary data over serial links (e.g., RS-232 or RS-485).
  • Application Scenarios: Widely used for devices that support serial communication, such as VFDs, smart meters, temperature controllers, and various PLCs.
  • E2C Trinity Support: E2C Trinity acts as a Master to connect and read data from slave devices via the gateway's serial port.

2. Prerequisites

Before starting the configuration, ensure the following preparations are complete:

  • Hardware Connection:
    • Ensure the E2C Trinity gateway's serial port (RS-485 or RS-232) is connected to the target device via shielded twisted pair cable.
    • Verify correct wiring (e.g., for RS-485, ensure A+ and B- are not reversed).
  • Serial Parameter Verification:
    • Confirm the target device's serial parameters: Baud Rate, Data Bit, Parity (Check Bit), and Stop Bit.
    • All devices on the same serial link must share the same serial parameters.
  • Tag List Preparation:
    • Obtain the Modbus register address table for the device.
    • Identify key parameters: Slave ID, Function Code, Register Address, and Data Type.

3. Configuration Steps

Follow these steps within the E2C Trinity Web interface.

Step 1: Create Device

  1. Log into the gateway management page. Navigate to [Data Acquisition] to enter the E2C Trinity configuration page.


  1. Click the "Create Device"button and fill in the connection information in the pop-up window.

Parameter Description Example
Name Name of the device for identification. Advantech-IO-01
Protocol Select "Modbus RTU". Modbus RTU
Connection Channel Select the corresponding physical serial port (e.g., Serial 1 or COM1). COM1
Slave ID The Slave Address of the device (Range: 1-247). 1
Poll Interval Frequency of data acquisition (Unit: Seconds). 10
High-speed DAQ Config Enable for millisecond-level acquisition. Note: Groups are auto-generated and tags cannot be modified after publishing. Enabled
High-speed Poll Interval Options: 50ms, 100ms, 200ms, 500ms. 100ms
Package Quantity Number of polls before reporting (Supports 10, 20, 30). 10
Comm. Interval Minimum interval between two communication requests (0-1000ms). 10
Batch Read Recommended to enable for improved efficiency. Enabled
Max Batch Size Max registers per request (Range: 2-125). 64
Byte Order Arrangement of data bytes (e.g., ABCD, BADC). Global default for this device. ABCD
Serial Parameters Displays Baud Rate, Data Bit, etc., based on the selected channel for verification. -
  1. Click "Save" to complete the device creation.

Step 2: Configure Tag (Point Table)

  1. Select the newly created device from the device list on the left.
  2. Click "Add" to create a single data acquisition Tag. Fill in the tag information.

Parameter Description Example
Name Unique identifier for the tag used in data reports. Inlet_Pressure
Acquisition Type Choose "High Performance" (if high-speed is enabled) or "Normal". Normal
Tag Type Device Tag (PLC data) or Virtual Tag (internal calculation). Device Tag
Function Code Select based on register type (e.g., 03 Holding Register). 03
Address Decimal Modbus address (e.g., 40001 corresponds to Address 1). 1
Data Type Must match the device (e.g., short, float). short (int16)
Invert Bool only: Flips the 0/1 status if enabled. Off
Decimal Places Float/Double only: Number of decimal points to display. 2
Encoding String only: Supports ASCII, UTF8, etc. UTF8
Length String only: Defines the string length to read. 10
Access Right Read Only, Read/Write, or Restricted by FC. Read Only
Unit Physical unit (e.g., Mpa, ℃, Hz). Mpa
  1. Repeat for all tags. Once finished, click "Publish" in the top right corner to apply the configuration.

4. Verification & Troubleshooting

Verification

  1. Check the device list to ensure the status is Online and tags are successfully collected.A green icon indicates success, and a red icon indicates failure.

  1. View the Latest Value column to verify data accuracy.

  1. Test Writing: Click the edit icon in the "Latest Value" column, modify the value, and verify if the PLC accepts the change.

Common Troubleshooting

  • Problem: Device fails to connect for a long time?
    • Check Physical Link: Ensure the gateway’s serial port (RS-485/RS-232) is securely wired to the device, and A+ / B- are not reversed.
    • Verify Serial Parameters: Confirm that the Baud Rate, Data Bit, Parity, and Stop Bit configured in the gateway match the slave device exactly.
    • Slave ID Confirmation: Ensure the "Slave ID" in the settings matches the device's actual hardware DIP switch or software ID.
    • Link Conflict: Check if multiple slave devices on the same RS-485 bus have conflicting Slave IDs.
  • Problem: Device is Online, but tag values are null or incorrect?
    • Verify Tag Parameters: Re-check the Function Code, Register Address, and Data Type against the device’s point table.
    • Byte Order Issues: If numeric values (like Float) are extremely large or garbled, try switching the "Byte Order" (e.g., from ABCD to CDAB or BADC) in the device settings.
    • Address Offset: Some devices have a ±1 address offset (e.g., PLC address 40001 might correspond to protocol address 0 or 1). Try adjusting the address slightly.
  • Problem: Data write failed?
    • Access Rights: Ensure the tag's "Access Right" is set to "Read/Write" or "Restricted by FC".
    • FC Support: Confirm the selected Function Code supports write operations (e.g., some Holding Registers are read-only on specific devices).
    • Write Protection: Check if the target device has a physical hardware lock or software-level write protection enabled.
  • Where to find logs?
    • Check the Debug Logs or System Logs in the management interface for specific error codes.

5. Appendix

Data Type Mapping

When configuring tags in E2C Trinity, use the following mapping:


E2C Trinity Data Type Length / Sign Device/PLC Type Typical Address Notes & Precautions
bool 1 bit BOOL / Coil 00001 / 10001 Coils are R/W; Discrete Inputs are Read-only. Supports Invert.
byte 8 bit Unsigned BYTE (USInt) - Pay attention to high/low byte mapping.
ushort (uint16) 16 bit Unsigned WORD (UInt) 40001 / 30001 16-bit aligned; Range 0–65535.
short (int16) 16 bit Signed INT 40002 / 30002 Range -32,768 to 32,767.
uint (uint32) 32 bit Unsigned DWORD (UDInt) 40003–40004 Requires 2 registers; Range 0–4,294,967,295.
int (int32) 32 bit Signed DINT 40005–40006 Range -2,147,483,648 to 2,147,483,647.
ulong (uint64) 64 bit Unsigned - 40006–40009 Occupies 4 consecutive registers.
long (int64) 64 bit Signed LINT 40010–40013 Occupies 4 consecutive registers.
float (float32) 32 bit IEEE REAL 40014–40015 May require Byte Order adjustment; supports Decimal Places.
double (double64) 64 bit IEEE LREAL 40015–40018 High variance in byte order across devices.
string 1...n Bytes STRING[n] From 40020 Stored by encoding; verify Encoding and Length.