AB-Controlnet - An Overview
ControlNet is an industrial fieldbus developed by Allen-Bradley to support highly deterministic and time-critical control applications. It is designed for systems that require predictable communication timing and guaranteed delivery of control data.
ControlNet communication is strictly scheduled and operates in repeating cycles called Network Update Intervals (NUIs), ensuring that critical data is exchanged at precise and repeatable intervals.
Physical and Link Layer
At the physical layer, ControlNet uses Manchester encoding and operates at a data rate of 5 Mbit/s. The link layer is optimized for cyclic data exchange, making ControlNet well suited for real-time automation and coordinated control systems.
Network Update Interval (NUI)
Each Network Update Interval is divided into three phases:
- Scheduled traffic for time-critical control data
- Unscheduled traffic for configuration, messaging, and diagnostics
- Maintenance for network management tasks
This structure guarantees bandwidth for deterministic control traffic while still allowing non-critical communication on the same network.
Data Frames and Application Layer
The maximum size of a scheduled or unscheduled ControlNet data frame is 510 bytes. At the application layer, ControlNet uses the Common Industrial Protocol (CIP), which is also used by DeviceNet and EtherNet/IP, enabling a consistent object model across these networks.
FAQ: ControlNet Overview
What is ControlNet used for?
ControlNet is used for deterministic industrial control applications that require predictable timing and guaranteed delivery of control data.
What makes ControlNet deterministic?
ControlNet uses scheduled communication within Network Update Intervals, ensuring time-critical data is transmitted at fixed and repeatable times.
What is a Network Update Interval (NUI)?
A Network Update Interval is the repeating communication cycle in ControlNet that contains scheduled, unscheduled, and maintenance traffic.
Which protocol does ControlNet use at the application layer?
ControlNet uses the Common Industrial Protocol (CIP), the same application layer used by DeviceNet and EtherNet/IP.