Profibus is a protocol that provides a seamless general-purpose manufacturing solution for master-slave communication tasks and Protocol Profiles which address the Process Automation, Safety and Motion Controls industries. Profibus is the fieldbus market leader with more than a 20% share of the market, approximately 400,000 equipped plants and more than 6 million nodes of more than 2000 available Profibus products from a wide range of manufacturers.

Profibus was created by a consortium of four companies and seven universities. Profibus FMS ( Fieldbus Message Specification ) was completed in 1989. A further step in1993 saw completion of the specification for the more simply configured and therefore considerably faster PROFIBUS DP protocol. Approximately 90% of Profibus slave applications in use are Profibus DP. This protocol is available in three functionally graded version; DP-V0, DP-V1 and DP-V2.

Profibus DP has been designed for high speed data exchange at the field level. This is where central programmable controllers, such as PLCs, PCs or process control systems, communicate with distributed field devices such as I/O, drives, valves, transducers or analysis devices, over a fast serial connection. Data exchange with the distributed devices is primarily cyclic.

The communication functions required for this are specified through the DP-V0 functions. These basic functions have been expanded step-by-step with special functions to produce DP-V1 and DP-V2. These versions largely reflect the chronological sequence of specification work as a result of the ever increasing demands of applications.

Version DP-V0, 1993

PROFIBUS DP-V0 provides the basic functionality of DP, including cyclic data exchange, station, module and channel-specific diagnostics and four different interrupt types for diagnostics and process interrupts.

With DP-V0 the DP master reads input information from the slaves cyclically and writes output information to the slaves cyclically. The bus cycle time for many applications is approximately 10ms. As an example a 10 station system with 128 byte I/O, 10,240 In/Out signials, running 12 Mbit/s has a bus cycle time of 2ms. Profibus DP can operate at baud rates ranging from 9600 to 12 Mbit/s and over a wide range of media including copper, plastic or glass fiber, a single network can reach distances of up to 15 kilometers. The comprehensive diagnostic functions of DP enable fast locations of faults. The diagnostic messages are transmitted over the bus and collected by the master. Profibus DP supports implementation of both mono-master and multi-master systems. This affords a high degree of flexibility during system configuration. A maximum of 126 devices can be connected to the bus with each slave capable of sending AND receiving 244 bytes of data.

There are three different device types in a Profibus DP system, DP master class 1, DP master class 2 and slaves. Class 1 master devices are PLC’s or PC’s they are the central controller that cyclically exchange information with the slaves, reading inputs and writing outputs. Class 2 master devices are engineering, configuration or operating stations. They are used during commissioning and for maintenance and diagnostics. A slave is a peripheral device that read process information and/or drives outputs.

Version DP-V1, 1997

PROFIBUS DP-V1 contains enhancements geared towards process automation, in particular acyclic data communication for parameter assignment, operation, visualization and interrupt control of intelligent field devices, in conjunction with cyclic user data communication.

Transmission of acyclic data is executed in parallel to cyclic data but with lower priority. This allows online access to stations using engineering tools. The class 1 master has the token and executes cyclic data exchange with each slave then it passes the token to the class 2 master. This master sets up an acyclic connection to any slave and exchanges data, it then passes the token back to the class 1 master. The class one master also as the capability to execute acyclic data exchange with slaves.

Profibus PA uses the Profibus DP-V1 protocol. Profibus PA is the Profile for Process Automation, typically with MBP-IS transmission technology. MBP is synchronous transmission with a defined transmission rate of 31.25 Kbit/s and Manchester coding. This transmission technology is frequently used in process automation since it satisflies the key demands of the chemical and petrochemical industries. PA is available for applications in process automation with a demand for bus power and intrinsically safe devices and is linked to the DP network with a coupler module. Tree or line structures and any combination of the two are network topologies supported by Profibus PA.

Modern process devices are intelligent and can execute part of the information processing in an automated system. PA supports acyclic data communication which allows parameterization and diagnostics of these intelligent devices over the Profibus network. The PA device profile defines the functions and parameters for different classes of process devices which allows plug and play of devices made by different manufacturers even in potentially explosive areas.

Version DP-V2, 2002

PROFIBUS DP-V2 contains enhancements primarily towards the demands of drive technology and safety systems. These enhancements include slave to slave communication, isochronous mode and clock management.

Slave to slave communications enables direct communication between slaves using broadcast communication eliminating the time overhead caused by need of having a master relay the information. A slave device acts as a “publisher”, the slave response does not go through the master but directly to other slaves configured as “subscribers”. This allows slaves to read data from other slaves and use this data as their own input. This reduces response time on the bus by up to 90%, opening up completely new application possibilities.

Isochronous mode enables clock synchronous control in masters and slaves irrespective of the bus load. It allows highly precise positioning processes with clock deviations of less than a microsecond. A “global control” broadcast message synchronizes all participating device cycles with the bus master cycle. Monitoring of the synchronization is done by a consecutive number “sign of life”.

The clock management function uses a real-time master to send out a time stamp to all slaves which synchronizes all stations to the system time with a deviation of less than a millisecond. This allows for the precise tracking of events.

The Profisafe profile uses Profibus DP-V2 protocol. Profisafe is an open solution for safety applications. It defines how fail-safe devices, emergency stop pushbuttons, Light arrays, overfill cutouts, etc., can communicate over Profibus with a failsafe controller so safely that they can be used for safety systems up to AK6 or SIL3.

The Profisafe profile was based on the IEC 61508 standard and relies on a statistical approach. Therefore an examination of the failure possibilities was necessary. It is possible for a message to get lost, appear repeatedly, be inserted additionally, appear in the wrong order or delayed and contain the wrong data. Profisafe uses the following four measures to monitor for and detect these possibilities.

1. The consecutive numbering of all safety messages.
2. A watch dog time for incoming messages and their acknowledgement.
3. A password code between sender and receiver.
4. An additional data protection CRC.

PROFINET, 2002

As automation technology continues to be reshaped by decentralization based on field bus technology the trend towards modular, reusable machines and plants with distributed intelligence will also continue.

Profinet fulfills the key demands of this trend.

• Consistent communications from field level through to corporate management level using Ethernet
• A vendor-independent plant-wide engineering model for the entire automation landscape
• Openness to other systems
• Implementation of IT standards
• Integration of Profibus and other field bus segments without the need to change them

Profinet uses common IT standards without defining a new field bus protocol on Ethernet. TCP/IP, UDP and the DCOM wire protocol are used for communicating on Ethernet. The OPC and XML standards are the basis for information exchange. Profibus, the leading field bus on the market, is completely integrated into the Profinet concept.

Profinet applies the most

Twenty three Profibus User Organizations consisting of more than 1100 members comprise Profibus International. These 1100 members represent vendors, end-users and academic institutions. In North America, the Profibus Trade Organization (PTO) consists of over 130 companies. Profibus truly represents the only total Worldwide Plantwide fieldbus.