Profibus Introduction

PROFIBUS has achieved wide acceptance in the world of automation engineering through its openness and its compatibility across manufacturers. PROFIBUS was developed as part of a joint fieldbus project. The aim of the project was the adoption of a standard. Today a wide range of different products from independent manufacturers are available that meet DIN 19245 Part 1 and 2. Operation of standard-compliant PROFIBUS devices within a bus system is ensured.

PROFIBUS defines the technical and functional characteristics of a serial fieldbus system for networking of distributed digital and analog field automation devices in the lower (sensor/actuator level) to medium performance range (cell level).

PROFIBUS distinguishes between master and slave devices. Master devices determine the data traffic on the bus.

A master may transmit messages without having received an external request when it is in possession of the bus access authorisation. Within the PROFIBUS protocol masters are also referred to as active devices.

Slaves are peripheral devices. Typical slave devices include sensors, actuators, measuring transducers, Beckhoff Bus Couplers BK3000, BK3100, BK3110, BK3010, and CX1500-B310 fieldbus connections. They have no bus access rights, i.e. they can only acknowledge received messages or transfer messages to a master on request. Slaves are also referred to as passive devices. Beckhoff Bus Couplers are passive devices that support PROFIBUS DP and PROFIBUS-FMS. They are also referred to as combined FMS/DP slaves.

Profibus DP

PROFIBUS-DP is designed for fast data exchange at the sensor / actuator level. Central control devices (such as, for example, programmable logic controllers) communicate here over a fast serial connection with distributed input and output devices. Data is mainly exchanged with these distributed devices cyclically. The central controller (master) reads the input information from the slaves, and writes the output information to the slaves. The bus cycle time must here be shorter than the central controller’s program cycle time, which in many applications is less than 10 ms.

A high data throughput is not in itself sufficient for successful use of a bus system. Ease of handling, good diagnostic facilities and secure transmission technology are also of the utmost importance if the user's demands are to be satisfied. These properties are ideally combined in PROFIBUS DP.

For the transmission of 512 bits of input data and 512 bits of output data distributed over 32 bus devices PROFIBUS-DP needs approx. 6 ms at a transmission rate of 1.5 Mbit/s or less than 2 ms at 12 Mbit/s.