The following information describes the operation of ProfiBus DP as it relates to Acromag Series 900PB DP slave I/O modules. For more detailed information on ProfiBus, you may refer to the ProfiBus Trade Organization at the PTO website www.profibus.com. Acromag manufactures a line of I/O modules that support Profibus DP over RS485. Feel free to visit our website at www.acromag.com to obtain the latest information about these and other Acromag products. Acromag Series 900PB modules utilize the popular ProfiBus DP FieldBus communication format. ProfiBus was created in 1989 by the German government in cooperation with several manufacturers of automation equipment. It is a messaging format specifically designed for high-speed serial I/O in factory and building automation applications. It is an open standard and is recognized as the fastest FieldBus in operation today. It is based on RS485 and the European EN50170 Electrical Specification. The DP suffix refers to “Decentralized Periphery”, which is used to describe distributed I/O devices connected via a fast serial data link with a central controller. To contrast, a programmable logic controller (PLC) normally has its input/output channels arranged centrally. By introducing a network bus between the main controller (master) and its I/O channels (slaves), we have decentralized the I/O. ProfiBus is based on universal international standards and oriented to the OSI (Open System Interconnection) reference model per international standard ISO 7498. In this model, every layer handles precisely defined tasks. Layer 1 of this model is the physical layer and defines the physical transmission characteristics. Layer 2 is the data link layer and defines the bus access protocol. Layer 7 is the application layer and defines the application functions. ProfiBus DP uses only layers 1 & 2 of this model, plus the user interface. Layers 3 to 7 are not used. A ProfiBus system uses a bus master to poll slave devices distributed in multi-drop fashion on an RS485 serial bus. A ProfiBus slave is any peripheral device (I/O transducer, valve, network drive, or other measuring device) which processes information and sends its output to the master. The slave forms a “passive station” on the network since it does not have bus access rights, and can only acknowledge received messages, or send response messages to the master upon request. It is important to note that all ProfiBus slaves have the same priority, and all network communication originates from the master. Acromag I/O modules form intelligent slave devices. Acromag modules implement the ProfiBus protocol via an industrystandard SPC3 ASIC from Siemens. This ASIC acts like a RAM or UART chip to the internal microcontroller and completely handles the requirements of the protocol standard. The ASIC will transfer network data to and from the microcontroller and automatically provide the response to the bus according to the ProfiBus specification.
ACROMAG (2002) Introduction to Profibus DP