Glossary · System coordination, integration and orchestration
Busy signal
Also known as: busy bit, occupied signal
German: Belegtsignal
In industrial automation, a busy signal is a status signal by which a system indicates that it is currently executing a task and cannot accept a new request. It is typically set when a request is accepted and reset when the task is finished or aborted.
- System integration
In one sentence
A busy signal shows that a system is executing a task and cannot accept a new request until it resets the signal.
Example
The vision system sets its Busy output during image evaluation; the PLC waits until Busy drops before reading the result and triggering the next image.
How it applies
- Engineering: Specify when the busy signal rises and falls relative to the request and completion signals, and what the partner does if the signal stays set too long. A Timeout on the busy phase detects hung devices.
- Commissioning: Check the timing with a logic analyzer or trace: a busy signal that rises one cycle too late lets the partner send a second request.
- Documentation: Include a timing diagram of request, busy and completion signals in the interface documentation. Service manuals should explain which state a stuck busy signal indicates and how to reset the device safely.
Busy signal vs. blocked state
A busy signal describes a device that is working on a task. A Blocked state describes a device that has finished and cannot release its output.