Interfaces and data transmission

A variety of interfaces are available for data transfer from the keyboard to the command-processing controller. Standard products on the consumer market are almost always equipped with the common USB interfaces. As other interfaces must be used depending on the application and technical conditions, such keyboards are often out of the question for more specialized applications due to their cable connection. The selection of possible transmission paths is large and very different. However, some technical principles apply equally to all interfaces.

For example, the commands for all interfaces are combined via an electrical matrix of row and column lines. This means that all possible keyboard commands can be compressed to just a few connections. For example, with a common 16x8 matrix, with which up to 128 keys can be realized, the data transmission to the microcontroller of the keyboard can take place via 24 lines. This mode of operation can be applied to almost all modern input devices with multiple keys. Pressing a key triggers a low electrical voltage in both the matrix column and the matrix row, which is read out by the controller. Possible voltage changes are continuously scanned by the controller and detected when the button is pressed.

In most applications, several buttons may be pressed at the same time. However, depending on the matrix arrangement and the connection used, this can lead to recognition problems. In the worst case, only a maximum of two simultaneous button presses are recognized, which is referred to as a 2-key rollover; in the best case, all buttons can be evaluated in parallel (n-key rollover). The reasons for these restrictions vary. For example, USB interfaces can only read a maximum of six simultaneous key presses due to a protocol.  The key rollover should therefore be taken into account when selecting a suitable interface.

 

As we offer all common interfaces for our input systems and can also install any customer-specific connection on request, we can manufacture a suitable keyboard for any special case. Depending on our customers' requirements, we equip our keyboards with the appropriate interface, the desired cable length, color and quality, so that our input devices can master any application.

We equip each of our keyboards with its own freely programmable controller. Our keypads are of course programmed and delivered ready for use, but on request we can also provide a tool with which our keypads can be programmed as required by our customers. As standard, we use the interface standards USB for our keypads, but we also offer EtherCAT, I²C, Profibus and CAN bus for customer-specific solutions.

USB (Universal Serial Bus)

This serial bus system is suitable for almost any type of data transfer and has established itself as a common standard due to precisely this flexibility and its continuous further development. The data transfer rate of the USB interface has been improved several times through modifications without losing downward compatibility, which means that the port has remained up-to-date for many years.

RS232 (Recommended Standard 232)

In the consumer market, this formerly widespread interface (the 9-pin D-Sub connector) is now almost extinct, as there are much faster and more compact alternatives. However, due to the low data rate, the relatively low cabling requirements and the high and tolerant signal level, the RS-232 is still in demand when it comes to interference immunity and long signal connections.

 

PS/2 interface

The PS/2 connection was also a widely used interface between keyboard and PC until the advent of the USB port, but has since been largely pushed out of the market. The six-pin mini-DIN connector is still preferable to USB for some applications, as it can transfer an unlimited key rollover.

 

EtherCAT (Ethernet for Control Automation Technology)

This real-time Ethernet is a protocol disclosed in IEC standard 61158 and is suitable for hard and soft real-time requirements in automation technology. EtherCAT enables particularly precise synchronization and cycle times of less than 100 µs.

 

I²C (Inter-Integrated Circuit)

A data bus mainly used internally for communication between different parts of the circuit. As an I²C microcontroller can control an entire network of integrated circuits with just two I/O pins and simple software, it has particularly low production costs.

 

Profibus (Process Field Bus)

This standard for fieldbus communication in automation technology is used in the manufacturing industry, among others, for fast communication in machines and systems between sensors/actuators and controllers of all kinds. The Profibus standards recommend using a 9-pin D-Sub connector for the connection.

 

CAN bus (Controller Area Network)

The background to the development of the CAN bus was to reduce cable harnesses and thus save production costs and weight. CAN protocols have established themselves in many safety-relevant areas, such as the automotive industry, medical, aircraft, aerospace and pyrotechnics, shipbuilding and rail vehicle construction, as well as in areas of automation technology.