Modbus/TCP metrics

Navigation: Configuration > IoT > Sources > Modbus/TCP metrics

This page defines the individual Modbus registers to be read from Modbus/TCP devices and maps each register to a metric and a data source. Each table row associates a specific register address, function code, and data type with a previously configured Modbus/TCP source and a named metric. The device polls these registers at the interval defined in the source configuration and publishes the resulting values to the configured IoT destinations. Before configuring entries on this page, at least one Modbus/TCP source and one metric must already exist on their respective pages.

Prerequisites

• At least one Modbus/TCP source must be configured on the Modbus/TCP sources page.
• At least one metric must be defined on the Metrics page.
• The Modbus register addresses, function codes, and data types of the target device must be known from its documentation.

Settings

Each row in the table defines one register-to-metric mapping. Click the + button to add a new entry.

Register

The Modbus register number, starting at 1. Note that some device documentation uses zero-based addressing. If the register address in the target device documentation starts at 0, decrease the value by one when entering it here.

Register type

The data width of the register.

A standard 16-bit Modbus register reads a single register. A 32-bit register reads two consecutive 16-bit registers and combines them into a single value. A bit selection reads a specific bit from a 16-bit register.

Modbus function code

The Modbus function code used to read the register.

Read holding register (3): Reads from the holding register area (function code 03).

Read input register (4): Reads from the input register area (function code 04).

Binary interpretation

Determines how the raw binary content of the register is interpreted as a numeric value.

The register content can be interpreted as a signed integer, an unsigned integer, or a signed floating point value. Select the interpretation that matches the data format documented by the target device manufacturer.

Modbus/TCP source

Selects the Modbus/TCP source from which this register is read. The available sources are those configured on the Modbus/TCP sources page and are identified by their IP address.

Metrics

Selects the metric to which the register value is mapped. If the dropdown list is empty, create a new metric on the Metrics page first.

ATTENTION

Modbus register numbering conventions differ between device manufacturers. Some documentation uses 1-based register numbers while others use 0-based addresses. Verify the addressing convention of the target device documentation and adjust the register number accordingly to avoid reading incorrect data.