PLC Communication Protocols & Networking Flashcards

Which industrial protocol uses a master/slave architecture over RS-485 serial communication and is widely supported by PLCs for connecting field devices?

Answer: Modbus RTU

Modbus RTU operates over RS-485 using a master/slave model and is one of the most widely supported serial protocols for PLC-to-field device communication.

EtherNet/IP is based on which application-layer protocol that maps industrial objects to standard Ethernet/TCP-IP?

Answer: Common Industrial Protocol (CIP)

EtherNet/IP uses the Common Industrial Protocol (CIP) as its application layer, running CIP messages over standard TCP/IP and UDP/IP Ethernet.

In PROFIBUS DP, what is the role of the 'master' device?

Answer: To initiate all data exchanges and poll slave devices for their input/output data cyclically

A PROFIBUS DP master controls bus access, cyclically requests I/O data from slaves, and sends output data to them.

What is the maximum number of nodes (devices) supported on a single PROFIBUS DP segment?

Answer: 126

A single PROFIBUS DP segment supports up to 126 nodes (addresses 0–125), with repeaters required to extend beyond one segment.

Which PLC networking protocol is specifically designed for real-time deterministic communication in motion control applications and uses a dedicated ring topology?

Answer: EtherCAT

EtherCAT (Ethernet for Control Automation Technology) achieves deterministic real-time performance using a ring topology where frames are processed on the fly by each node.

What does OPC-UA provide that traditional OPC (OPC Classic) did not?

Answer: Platform-independent, service-oriented communication with built-in security and no dependency on COM/DCOM

OPC-UA is platform-independent (not Windows COM/DCOM dependent) and includes security (encryption, authentication) and a flexible information model natively.