PROFIBUS-PA (Process Automation) uses synchronous transfer mode technology, as defined in IEC 61158-2, to communicate between field devices and the RS 485 backbone of PROFIBUS-DP. A segment coupler, or gateway is installed to bridge PROFIBUS-DP with PROFIBUS-PA. Otherwise, the protocols are identical, allowing transparent communication between general purpose automation systems and decentralized field devices.
PROFIBUS-PA is a master-slave bus. Transmitters used in the process industry are typically slave devices or passive stations which only communicate at the request of the master.
General Layout Topologies
The topology for PROFIBUS-DP is a linear bus. Branching can be accomplished with repeaters or, in the case of PROFIBUS-PA, this can be accomplished with the segment couplers. The PROFIBUS-PA topology follows the physical layer as defined in ISA SP50.02. Daisy chain or star topologies are allowed.