Introduction to Industrial Automation

8.2.1   Master/Slave Method of Access

According to the Master/Slave protocol, a PLC in a communication network is defined as the 

master PLC, and thus all the remaining PLCs become slaves, as shown in Figure 8.5. The PLC 

defined as the master station controls the bus traffic entirely. The master PLC with a predefined 

order gives the control of the bus to the rest of the PLCs, and thus the ability to communicate to 

each slave PLC. The slave PLC acquires the exclusive use of the network for some definite time and 

distributes the information that is required by the corresponding application to the other PLC/

PLCs in the network.