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What is Modbus TCP?

Modbus TCP is an industrial communication protocol that enables data acquisition from industrial devices over TCP/IP networks. It provides a standardized method for reading data from PLCs, sensors, and other industrial equipment using Ethernet infrastructure.

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Device Profile Configuration

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Connection Parameters

Configure the communication settings for your Modbus TCP device:

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Data Format Options

The DataFormat parameter determines how multi-register values are interpreted:

• ABCD: Big-endian, high word first (default)
• BADC: Big-endian, low word first
• CDAB: Little-endian, high word first
• DCBA: Little-endian, low word first

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Tag Configuration

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Basic Tag Settings

Each tag represents a data point from your Modbus device and requires:

1. Name: Descriptive identifier for the data point
2. Address: Modbus address specification
3. Data Type: Type of data to read
4. Length: Number of registers to read (for String/Bytes only)
5. Polling Interval: Individual polling frequency (0 = use device default)

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Address Format

[s=station];[x=function];address[.bit]

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Address Components

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Function Codes

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Address Examples

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Data Types

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Fixed-Size Data Types

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Variable-Length Data Types

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Configuration Examples

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Temperature Sensor

{
  "Name": "Temperature",
  "Address": "s=1;x=4;100",
  "DataType": "Float",
  "Length": 0,
  "PollingInterval": 1000
}

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Pump Status

{
  "Name": "Pump Status",
  "Address": "s=2;x=1;50",
  "DataType": "Bool",
  "Length": 0,
  "PollingInterval": 500
}

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Device Name String

{
  "Name": "Device Name",
  "Address": "s=2;x=4;400",
  "DataType": "String",
  "Length": 10,
  "PollingInterval": 5000
}

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Energy Counter

{
  "Name": "Energy Counter",
  "Address": "s=1;x=4;500",
  "DataType": "UInt",
  "Length": 0,
  "PollingInterval": 2000
}

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Variable-Length Data Configuration

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String Data Type

• Length: Number of registers to read for string data
• Character Count: Each register contains 2 ASCII characters
• Total Characters: Length × 2

Example: Length = 5 reads 5 registers containing 10 characters

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Bytes Data Type

• Length: Number of registers to read for binary data
• Byte Count: Each register contains 2 bytes
• Total Bytes: Length × 2

Example: Length = 4 reads 4 registers containing 8 bytes

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Advanced Features

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Bit-Level Reading

Read specific bits from registers by adding .bit to the address:

Address: 100.5
Data Type: Bool

This reads bit 5 (0-indexed) from holding register 100.

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Dynamic Data Format

Override the default data format for specific tags:

Address: format=BADC;s=2;100
Data Type: Float

This reads a float value using BADC byte order instead of the default ABCD.

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Best Practices

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Performance Optimization

1. Group Sequential Addresses: Place related tags in consecutive registers
2. Optimize Polling Intervals: Use appropriate frequencies based on data change rates
3. Minimize Station Queries: Group tags by station number
4. Use Appropriate Data Types: Choose the most efficient data type
5. Exact Length Sizing: Set Length to match exact data size for String/Bytes

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Polling Interval Guidelines

• Critical Data: 100-500ms for critical process data
• Status Information: 1-5 seconds for status monitoring
• Configuration Data: 10+ seconds for slowly changing data

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Length Parameter Guidelines

• String: Set Length based on expected text length
• Bytes: Set Length based on binary data size
• Performance: Avoid unnecessarily large Length values
• Device Limits: Check device documentation for maximum register ranges

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Troubleshooting

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Connection Issues

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Data Reading Errors

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Diagnostic Steps

1. Network Connectivity: Ping the device IP address
2. Port Accessibility: Verify port 502 is accessible
3. Address Validation: Check device memory map documentation
4. Function Code Testing: Try reading with different function codes
5. Data Format Testing: Test different byte order options
6. Length Validation: Ensure Length parameter is correct for variable data types

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Technical Specifications

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Protocol Compliance

• Modbus TCP: Full compliance with Modbus Application Protocol v1.1b3
• Message ID Management: Automatic increment for request tracking
• Error Detection: TCP-based error handling and timeout management
• Data Integrity: Built-in validation and retry mechanisms

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Performance Characteristics

• Maximum Tags: Limited by device capacity and network bandwidth
• Update Rate: Configurable from 100ms to 60 seconds per tag
• Concurrent Devices: Multiple device connections supported
• Data Throughput: Optimized for industrial monitoring applications

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Memory Areas