Operating mode

In a bus system, the bus nodes share the transmission medium. The bus access control defines when a bus node can have access to the transmission medium. PROFIBUS uses a hybrid access method for this purpose (token passing with subordinate master-slave).

The access method distinguishes between:

• Active bus nodes (masters) and
• Passive bus nodes (slaves).

In each case, an active station is granted access to the bus by the permission to send (token). Once a specified time has elapsed, it passes the permission to send on to the next active station in the bus system. If there is no request to send, the token is passed on immediately to the next master module.

Passive nodes such as ET 200 distributed I/O devices do not receive transmission rights. They are accessed direct by the master module to which they are assigned.

Configuration

There are helpful and easy-to-use tools available to the user for configuring, parameterizing, starting up and diagnosing the PROFIBUS DP field bus system.

For the master interfaces of SIMATIC S7, the STEP 7 programming software is used.

With SIMATIC S7 and PROFIBUS DP, programmable controllers are merging more closely with the field technology. All the functions for configuring the fieldbus system are already integrated in the STEP 7 programming software.

For master interfaces of SIMATIC S5, the COM PROFIBUS parameterization software is used. It enables easy, menu-driven parameter assignment for the PROFIBUS DP field bus with a SIMATIC S5 master and the IM 308-C interface module as well as with the S5-95U/DP master programmable controller.