Discrete -or Factory Automation- is typically characterized by faster processes than process applications. Here we use PROFIBUS DP (Decentralized Periphery). The most prevalent medium for PROFIBUS transmission is over copper wire, and for this, the easy-to-use and cost-effective RS-485 transmission technology is used. We are able to transport 244 bytes of data from 9600 bit/s up to 12 Mbit/s. This range of speeds can accommodate nearly every application. There are some instances under which wired transmission technology reaches its limits, for example in an environment with heavy interference or when bridging long distances. In these cases, optical transmission via fiber cables is available.
The communication basis for PROFIBUS lies in the cyclic data exchange between PLCs (masters) and devices (slaves). A cycle will consist of a master sending outputs to, and receiving inputs from all of it’s devices, and then repeating the cycle. This also includes device-, module-, and channel-specific diagnostics (e.g. wire break, short circuit, etc.) for quick fault localization. All field devices have the same priority, and every device is scanned every cycle. “DP-V0” is the base protocol for cyclic I/O and diagnostics.
This is further extended in “DP-V1” which allows for the acyclic exchange of data between PCs or PLCs and slave devices. This also includes the on-demand access of device parameters, and the setting of alarm limits. Finally, the “DP-V2” extension provides the capability for slave-to-slave communication in a broadcast Publisher/Subscriber fashion. DP-V2 applications include motion control and other high-speed requirements.
For a deeper overview read the PROFIBUS System Description: