Modbus TCP

The Modbus TCP protocol in InDataX enables communication with a wide variety of industrial devices over Ethernet networks. This driver is versatile, supporting both standard TCP/IP and TCP over RTU (encapsulated) connections.

Connection Parameters

To configure the Modbus TCP communication channel, define the following fields:

• Name: Unique identifier for the protocol.
• Connection Type: Select between TCP/IP (standard) or TCP over RTU (if the Modbus RTU device is behind a gateway).
• IP Address: The IP address of the slave device or gateway.
• Port: The listening port (usually 502).
• Modbus Slave ID: The device identifier (Unit ID), usually 1.

Variable Configuration

Data access in Modbus is performed through registers. InDataX allows for simple mapping of these registers:

• Name: Name of the variable in InDataX.
• Type: Data type for conversion (Real, Integer, Boolean, etc.).
• Record Value: Inclusion in the Thing's historical logs.
• Modbus Address: Numerical address of the starting register.
• Length: Number of registers that make up the variable (e.g., 2 registers for a 32-bit value).
• Register Type:
  • Coil: Output bits that allow reading and writing (e.g., activating a relay).
  • Discrete Input: Read-only input bits (e.g., status of a digital sensor).
  • Holding Register: 16-bit registers that allow reading and writing. This is the most common type for setpoints and configurations.
  • Input Register: 16-bit read-only input registers for process data (e.g., analog sensor values).
• Signed: Indicates whether the value should be interpreted as a signed number (positive/negative).

Register vs Address

Make sure to check whether your device's manual uses 0-based or 1-based addressing, as this is often the most common cause of reading errors.

Configuration Example

Below are common examples of how to map industrial data using Modbus TCP:

Variable	Type	Address	Length	Register Type	Notes
oven_temperature	Real	100	2	Holding Register	A 32-bit value occupies two 16-bit registers.
motor_status	Boolean	10	1	Coil	Reading/Writing an individual output bit.
flow_rate_m3h	Integer	200	1	Input Register	16-bit read-only value from a sensor.
digital_input	Boolean	5	1	Discrete Input	Status of a read-only physical contact.

Byte Order (Endianness)

In Modbus TCP, when reading 32-bit values (like Reals), the order of registers or bytes can vary depending on the manufacturer (Little-Endian vs. Big-Endian). If you get incoherent values, you may need to adjust the reading order in the system logic.