Modbus RTU

The Modbus RTU protocol in InDataX enables communication with industrial devices via serial interfaces such as RS-485 or RS-232. This protocol is the standard for integrating instrumentation, frequency inverters, and "legacy" devices over fieldbus.

Connection Parameters

To configure a Modbus RTU channel, define the following serial parameters:

• Name: Unique identifier for the protocol.
• USB Port (Connection Order): InDataX uses the physical connection order of USB-to-Serial adapters (0, 1, 2...) to ensure the system always assigns the same channel to the same hardware, regardless of the port name assigned by the operating system (COM).
• Baud Rate: Transmission speed (e.g., 9600, 19200, 115200).
• Parity: Selection between None, Even, or Odd.
• Data Bits: Usually 8.
• Stop Bits: Usually 1 or 2.
• Modbus Slave ID: The device's address on the bus (Station ID).

Variable Configuration

Variable management is identical to Modbus TCP, based on register mapping:

• Name: Variable identifier.
• Type: Data format (Real, Integer, Boolean, Long, etc.).
• Record Value: Enables logging in the historical database.
• Modbus Address: Numerical address of the register.
• Length: Number of registers (16 bits each) the variable occupies.
• Register Type:
  • Coil: Output bits (read/write).
  • Discrete Input: Read-only input bits (e.g., status of a digital sensor).
  • Holding Register: 16-bit registers (read/write).
  • Input Register: 16-bit registers (read-only).
• Signed: Defines whether the value includes a negative sign.

Configuration Example

Variable	Type	Address	Length	Register Type	Application
frequency_hz	Real	4001	2	Holding Register	Reading frequency from an inverter.
start_stop	Boolean	1	1	Coil	Remote motor control.
current_a	Integer	500	1	Input Register	Line current measurement.
door_sensor	Boolean	20	1	Discrete Input	Status of a limit switch.

Bus Termination

In RS-485 networks, remember to install termination resistors (usually 120Ω) at the ends of the bus to prevent signal reflections and communication errors, especially for long cable runs or high speeds.