Modbus TCP

Modbus TCP is a widely used industrial protocol for communicating with PLCs, sensors, and other field devices over TCP/IP networks.

Configuration fields

Field	Default	Description
Host	—	IP address or hostname of the Modbus server
Port	502	TCP port number. The standard Modbus TCP port is 502.
Slave ID	1	The Modbus unit/slave identifier (1–247). Identifies the target device on the network.
Timeout (ms)	—	Optional connection timeout in milliseconds

Endpoint format

The connector endpoint is formatted as host:port:

192.168.1.50:502
10.0.0.100:502
modbus-server.local:502

Register types

Modbus devices organize data into four register types:

Register Type	Address Range	Access	Data
Coils	00001–09999	Read/Write	Single bit (on/off)
Discrete Inputs	10001–19999	Read only	Single bit (on/off)
Input Registers	30001–39999	Read only	16-bit word
Holding Registers	40001–49999	Read/Write	16-bit word

Data formats

Modbus registers store 16-bit values. Multi-register values are assembled from consecutive registers:

Format	Registers	Description
16-bit integer	1	Single register, signed or unsigned
32-bit integer	2	Two consecutive registers
32-bit float	2	IEEE 754 single-precision floating point
String	N	Multiple registers, 2 ASCII characters per register

Connector configuration form

When creating or editing a Modbus TCP connector, the protocol-specific configuration form includes:

Field	Default	Description
Host	—	IP address or hostname of the Modbus server
Port	502	TCP port number
Unit ID	1	The Modbus unit/slave identifier (1--247)
Timeout (ms)	—	Optional connection timeout in milliseconds

Using with bindings

When binding variables to Modbus data points, the binding editor provides a protocol-specific address form with the following fields:

Field	Description
Register Type	Holding Register, Input Register, Coil, or Discrete Input
Start Address	The register address number (for example, 40001)
Data Format	How to interpret the register value: 16-bit integer, 32-bit integer, 32-bit float, or string
Byte Order	For multi-register values: Big Endian or Little Endian
Word Order	For multi-register values: High Word First or Low Word First

Byte order and word order fields appear only when the selected data format spans multiple registers (for example, 32-bit float or 32-bit integer).

Modbus register addressing and byte order can vary between device manufacturers. Consult your device documentation for the correct register map and data format.