Modbus RTU data organization
These concepts define how data in your device is accessed by the Anybus ONE System on Module over Modbus RTU.
Modbus registers
Modbus RTU uses a 16‑bit, zero‑based address (0–65 535) for each register type.
The register type defines how the data is accessed.
Supported register types:
Coils: Read/write binary outputs
Discrete inputs: Read‑only binary inputs
Input registers: Read‑only data values
Holding registers: Read/write data values
Each register type has its own address space, identified by its Modbus prefix.
Parameters
A parameter represents a logical value inside your device. Each parameter is assigned a register address and a data type. The data type determines how many registers the parameter occupies and how the value is represented and interpreted.
Data sets
A data set groups related parameters into a structured block. Use data sets to group parameters for combined transfer and improved efficiency.
Data sets are required for cyclic communication to ensure data consistency when multiple parameters are transferred together. Data sets can also be accessed acyclically.
The direction of a cyclic data set can be Input or Output.
Types of data
The Modbus RTU host interface transfers data that can be converted by the Anybus SoM into two different formats when mapping to industrial network protocols.
Access type:
Cyclic transfer
Read and written using Modbus request/response operations
Grouped into data sets with consecutive Modbus register addresses
Transferred in a single Modbus read or write operation to ensure data consistency
Acyclic access
Read or written on request
Used for data accessed on request, such as parameterization, diagnostics, and configuration
Does not require grouping into data sets
Both cyclic and acyclic access rely on the Modbus RTU configuration defined in Anybus Studio.
How Modbus RTU communication is performed
The Anybus System on Module acts as the Modbus RTU client and initiates all read and write operations.