Which protocol gives control servers and the SCADA host the ability to query and change configurations of each PLC over a network?

Which protocol gives control servers and the SCADA host the ability to query and change configurations of each PLC over a network?

• A. Ladder Logic
• B. Modbus
• C. Fieldbus
• D. CAN

Answer: (B)

The central idea is that Modbus provides a master/slave (client/server) protocol that lets a SCADA system query and configure PLCs over a network. In Modbus, the SCADA host acts as the master and sends requests to each PLC (the slaves) to read data or to write values that configure operating parameters. This setup supports centralized monitoring and remote configuration across multiple devices, which is exactly what the question describes. Function codes like Read Holding Registers and Write Multiple Registers map directly to retrieving current settings and updating configuration data on the PLCs, respectively.

Ladder Logic isn’t a network protocol; it’s a programming language used to implement control logic inside a PLC. Fieldbus refers to a family of industrial networking standards for device-to-device communication, but it’s a broad category rather than the specific master/slave mechanism used for querying and changing PLC configurations over a network. CAN is mainly used in automotive and embedded networks and isn’t the standard choice for SCADA-to-PLC configuration over an IP-based network.

So, Modbus is the protocol that best fits the described capability.