Glossary · Automation fundamentals, platforms and components
Register
Also known as: Holding register, Processor register
German: Register
In computing and industrial communication, a register is a small, addressable storage location of fixed width. In processors it holds operands and results; in protocols such as Modbus, registers are 16-bit data locations (holding registers, input registers) through which devices exchange values.
- Automation components
In one sentence
A register is a fixed-width storage location, in a processor or a device such as the 16-bit holding and input registers in Modbus.
Example
The energy meter publishes active power as a 32-bit float spread over two Modbus holding registers, and the documentation states the word order.
How it applies
- Engineering: Device integration often means mapping registers: address, data type, scaling, unit and access rights. Values larger than 16 bits span several registers, and byte and word order differ between vendors.
- Commissioning: Off-by-one addressing (0-based vs. 1-based register numbers) and swapped word order are classic errors. Test with known values first.
- Documentation: A register map in the device manual is an interface specification. List address, name, Uint or other data type, unit, Scaling factor, read/write access and default value, and state the addressing convention used.
Register vs. data model
A register map describes where raw values are stored. A Data model, as in OPC UA, also describes what the values mean and how they relate, so clients need less out-of-band documentation.