Glossary · Industrial communication
Fieldbus master
Also known as: Bus master, Controller (fieldbus), Scanner
German: Feldbus-Master
In industrial communication, a fieldbus master is the node that controls data exchange on a fieldbus: it initiates communication with the connected slave devices, collects their input data and sends output data. Newer specifications often use the terms controller, main device or scanner instead.
- Industrial communication
In one sentence
A fieldbus master controls data exchange on a fieldbus by polling or scheduling the connected slave devices.
Example
The PLC's PROFIBUS DP interface acts as fieldbus master and cyclically exchanges I/O data with 16 drives configured as slaves.
How it applies
- Engineering: The master holds the bus configuration: which slaves exist, their addresses, data lengths and parameters. On some systems several masters share a bus with token passing; on others only one master is allowed.
- Commissioning: Configuration files of all slaves are imported into the master's engineering tool. A slave that isn't configured is ignored or causes an error, depending on the system.
- Operation: The master monitors each slave and reports communication failures. Programs should evaluate these diagnostics rather than rely on silently frozen input values.
- Documentation: The documentation team states which role a device supports (master, slave or both) and uses the terminology of the relevant specification. Many organizations now prefer terms such as controller and device, or main device and subdevice; choose one pair and use it consistently.
Fieldbus master vs. fieldbus slave
The master initiates communication; the Fieldbus slave responds. In EtherCAT the terms main device and subdevice are used, in PROFINET IO controller and IO device, in EtherNet/IP scanner and adapter.