Glossary · Industrial communication
Fieldbus slave
Also known as: Bus slave, Field device (fieldbus), Subdevice
German: Feldbus-Slave
In industrial communication, a fieldbus slave is a device on a fieldbus that doesn't initiate cyclic data exchange itself but responds to the fieldbus master, sending its input data and receiving output data. Newer specifications often call it a device, subdevice or adapter.
- Industrial communication
In one sentence
A fieldbus slave is a device that responds to the fieldbus master, sending its inputs and receiving outputs on request.
Example
A valve terminal configured as a PROFIBUS DP slave receives its output byte from the PLC and returns its diagnostic status in every bus cycle.
How it applies
- Engineering: Each slave is described by a device description file (for example GSD, EDS or ESI) that tells the master's tool which data and parameters the device offers.
- Commissioning: The slave's Node address must be unique and match the master configuration. Many slaves also need parameters that the master writes at startup.
- Operation: When the master stops communicating, a slave sets its outputs to a configured substitute state after a watchdog time. This behavior must be chosen with the machine's hazards in mind.
- Documentation: The documentation team describes the slave's data image, parameters, substitute value behavior and diagnostic indicators, and provides the device description file in a current version.
Fieldbus slave vs. fieldbus master
The Fieldbus master initiates and schedules communication; the slave only responds. Terminology differs by system: IO device (PROFINET), adapter (EtherNet/IP), subdevice (EtherCAT). Technical writers should follow the terms of the specification they document.