Introduction to Industrial Automation

8.3.6   The Profibus Network

Except for interconnection of sensors and actuators, there is a big need for interconnecting control-

lers of all kinds that exist at the level of control of a production process, such as robot controllers, 

industrial PCs, PLCs, CNC machine controllers, programming devices of PLCs, etc. At this level 

of a computer integrated industrial environment, strong communication abilities are required, 

such as a large volume of data, real-time high speed, a large number of nodes, and a large range. 

One of the networks with such characteristics is the Profibus network for a wide range of indus-

trial applications in manufacturing, process, and building automation. A PLC can communicate 

with machines from different manufacturers via a Profibus network that is a vendor-independent 

fieldbus standard without the need for special adaptive settings. A typical Profibus network con-

figuration is shown in Figure 8.12. In the Profibus network, there is separation of PLCs on master/

slave units. The token passing procedure is used for the communication of master PLCs. The mas-

ter PLCs designate the data communication on the bus, and can transmit messages without the 

need for external requests when the PLC has the access rights (token) to the bus. Slave units may 

be peripheral devices such as PLCs, I/O devices, servo drives, inverters, and temperature control-

lers. These devices do not have direct access to the bus, except for the cases where it is requested by 

the master PLC. The master PLC sends messages to the slaves, who send acknowledgment or send 

response messages to the master upon corresponding requests.