Key Decisions for PROFINET Developers

Device manufacturers wanting to equip an automation device with a PROFINET interface have different options for implementation. Before deciding on a specific implementation method, it’s important to first determine which functions will be supported by the PROFINET automation device:

Real-Time Requirements

IEEE 802.3 ensures problem-free communication between PROFINET automation devices and among PROFINET automation devices and other standard Ethernet devices. For applications with very stringent real-time requirements, PROFINET offers mechanisms that enable both standard and real-time communication to take place in parallel. Communication with PROFINET can, therefore, be scaled using three different performance levels, which build on each other:

› The transmission of engineering data and non-time-critical data occurs over TCP/IP. This standard communication is possible between all automation devices.
› The real-time (RT) channel is available for the transmission of process data.
› Isochronous real-time communication (IRT) for isochronous applications like motion control. This enables a clock rate of < 1 ms and a jitter of < 1 µs. IRT capability is based on hardware support in the device.

Conformance Classes

PROFINET defines three Conformance Classes that build upon one another. Each class has a functional scope determined for the typical area of application.

CC-A: Use of the infrastructure of an existing Ethernet network, including integration of basic PROFINET functions. All IT services available without restriction.
CC-B: The functional scope of CC-B comprises the functions of CC-A, plus it supports easy user-friendly device replacement without the need for an engineering tool. Furthermore, the Simple Network Management Protocol (SNMP) supports extended device diagnostics of network functions.
CC-C: The functional scope of CC-C comprises all the functions of CC-B, plus it supports high-precision and deterministic data transmission, including isochronous applications.

Implementation Options

Depending on the functionality required (Conformance Class), it is essential to select the suitable type of implementation for each individual case.

In principle, the following options are also available:
1: Standard microcontroller unit (MCU) with integrated or external standard Ethernet controller or FPGA
2: FPGA with internal or external standard or IRT-capable switch
3: Module with a standard microcontroller or with a microcontroller with IRT hardware support
4: ASIC with IRT hardware support and IRT-capable switch

Development Path

Each of the implementation methods can be realized in a different way. When selecting the most suitable method for the particular case in question, the expected production costs, the development time, and the resulting time to market must be taken into account. Three different methods are the following:

Customer-specific/individual design: The implemented PROFINET interface is embedded in a hardware and software design that has been optimized with regard to development expenditure and time to market using commercially available software solutions and standardized discrete or FPGA-based hardware design schemes.

Embedded module design: The implemented PROFINET interface is embedded in a design that has been optimized for flexibility and time to market-based on preassembled commercially available communication modules.

External couplers: The PROFINET interface is implemented without accessing the device electronics based on external couplers and using an adapter connected in series

Read more about PROFINET development  HERE