PLC PLC Communication Protocols & Networking

Question 1

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

Accepted Answer

Modbus RTU

Answer

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.

Question 2

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

Accepted Answer

Common Industrial Protocol (CIP)

Answer

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

Question 3

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

Accepted Answer

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

Answer

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

Question 4

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

Accepted Answer

126

Answer

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

Question 5

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

Accepted Answer

EtherCAT

Answer

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.

PLC - Programmable Logic Controller Certification Practice Test

PLC - Programmable Logic Controller Certification Practice Test

PLC PLC Communication Protocols & Networking