To ensure that electronic devices function correctly and execute the right command in every situation, they need a control system. The classic wiring of cables and switches, the connection-programmed controller (VPS), is increasingly being replaced by the programmable logic controller (PLC). Instead of physical connections between the switches, the processes are programmed digitally. This not only makes it lighter, but also significantly more versatile and quicker to modify.

A PLC is basically a robust process computer, an industrial computer designed for continuous operation. It consists of an operating system (firmware), signal inputs and outputs and an interface. This enables communication with the user program, defines the physical characteristics of the data lines and translates, so to speak, between the user and the controller.

Depending on the application, there are a variety of different interfaces. They differ in transmission rate and distance.

EIA-232, also known as RS 232, is a serial interface that used to be common in the computer sector. It is suitable for low transmission rates over short distances of up to several meters. Initially, signals were transmitted via 25-pin connectors, later via 9-pin connectors, which were also commonly used in the computer sector until a few years ago. The binary signals (0 and 1) are described using different voltage states. The standards are defined by the US Electronic Industries Alliance (EIA), which previously used the term Recommended Standard (RS).

EIA-485, also known as RS 485, is a serial interface for low-cost data communication with high transmission rates in the range of several megabits per second, sometimes even gigabits per second. Because EIA-485 uses a pair of wires instead of a single conductor, it is less susceptible to interference and is also suitable for longer transmission paths. In contrast to other interfaces, such as RS 232, the pin assignment and protocol are not defined and can vary with the application.

EtherCAT (Ethernet for control automation technology) is an extension of the local Ethernet network. It allows several data stations, for example computers or other electronic devices, to communicate with each other simultaneously. Due to its functional principle, Ethernet is subject to certain restrictions for real-time applications. In classic Ethernet, data packets are first received, interpreted and then the process data is copied. To speed up this process, Beckhoff developed the EtherCAT system. This allows the devices connected to the network to extract the data intended for them in real time. The delay during processing is thus reduced from several microseconds (millionths of a second) to a few nanoseconds (billionths of a second).