Which field-network protocol enables data exchange between PLCs across a network, facilitating control operations?

• A. Modbus
• B. Fieldbus
• C. SCADA
• D. CAN

Answer: (B)

This question centers on how devices at the field level communicate to coordinate control. Fieldbus is the umbrella for industrial field-network protocols that connect PLCs and field devices over a network, allowing real-time data exchange and control signals across multiple controllers. This shared data and messaging backbone lets PLCs coordinate operations, such as sharing sensor readings, I/O status, and commands to actuators, to achieve synchronized control of a process.

Modbus is a widely used protocol that can run over field networks, but it’s a specific protocol rather than the whole family of field networks. SCADA refers to the supervisory system that interfaces with controllers, rather than the network protocol itself. CAN is a particular fieldbus used mainly in automotive contexts, with a more limited scope in typical plant automation. Therefore, fieldbus best fits the concept of enabling PLCs to exchange data across a network to support control operations.