PROFIBUS DP

The PROFIBUS DP (RS485) is responsible for communication between the Controller level of a process automation system and the decentralized periphery in the field, also intrinsic safety (RS485-IS) via DP-Ex barriers into hazardous area.

One feature of PROFIBUS DP is its scalable high speed of transmission up to 12 Mbit/s.

Each device, connected to a PROFIBUS network, needs a unique address for selectively identify a field device. For this purpose, PROFIBUS device addresses are assigned either by an address switch (hard addresses) or by parameter assignment during commissioning (soft addresses).

A 7-bit device address serves to identify the bus participants in the network. The addresses range from 0 to 127 and the following are reserved:

• Address 126: default for automatic address assignment via the master;

• Address 127: sending broadcast telegrams.

If the address 0 is used for the class-1 master, the addresses 1 to 125 are available for addressing the field devices. Therefore up to 126 DP or PA field devices (master and slaves) can be addressed. Each address can only be used once in a single PROFIBUS network.

RS485 is the most commonly used transmission technology for PROFIBUS DP. It uses a shielded twisted pair copper cable and enables transmission rates up to 12 Mbit/s. Because of its simply installation it is cost-effective and requires no expert knowledge.

The bus structure allows adding or removing of field devices as well as step by step commissioning without influencing the system. Later extensions have no impact on devices that are already working on the bus. RS485 is scalable in its transmission rate from 9.6 kbit/s up to 12 Mbit/s, which is set in the PROFIBUS master.

NOTE: In a PROFIBUS DP installation, a data transfer rate must be chosen which is supported by all devices connected to the bus. The chosen data transfer rate then determines the maximum segment lengths as shown above.