Basics of interfaces and data transmission

A large number 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 usual USB interfaces. Since other interfaces have to be used depending on the application and the technical conditions, such keyboards are often out of the question because of their cable connection for more specific applications. The selection of possible transmission paths is large and definitely brings with it differences. However, some technological principles apply equally to every interface.

For example, for all interfaces, the commands are bundled using an electrical matrix of row and columns. This enables the compression of all possible key commands to a few connections. For example, with the help of a common 16x8 matrix with which up to 128 keys can be implemented, data can be transferred to the microcontroller of the keyboard with 24 lines. This functionality can be used on almost all modern input devices with several keys. Pressing the button triggers a low electrical voltage in the matrix column as well as in the row, which is read by the controller. Possible changes in voltage are continuously scanned by the controller and perceived when a button is pressed.

In most applications it can happen that several buttons are pressed at the same time. 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 key presses are recognized, this is referred to as a 2-key rollover, in the best case all keys can be evaluated in parallel (n-key rollover). The reasons for these restrictions are different. For example, USB interfaces can only read out a maximum of six simultaneous key presses based on a protocol. The key rollover should therefore be taken into account when selecting a suitable interface.

Our interface technologies in standard products

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

We equip each of our keyboards with its own, freely programmable controller. Our typing keyboards are of course programmed and delivered ready for use, but on request we can also provide a tool that our customers can use to program our keypads. The USB, PS/2 and RS232 interfaces are the standards we install on our keyboards, but we also offer EtherCAT, I²C, Profibus and CAN bus for customer-specific solutions.

RS232 (Recommended Standard 232)

In the consumer market, this previously widespread interface (the 9-pin D-Sub connector there) is now almost extinct, as there are far faster and more compact alternatives. 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 noise immunity and long signal connections.

PS/2 interface

The PS/2 connection was also a widespread interface between keyboard and PC until the USB port was introduced, but has since been largely replaced by the market. The six-pin mini-DIN connector is still preferable to USB for some areas of application, since it can transmit an unrestricted key rollover.

USB (Universal Serial Bus)

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

Our other options for customer-specific solutions

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 circuit parts. Since an I²C microcontroller can control an entire network of integrated circuits with only two I/O pins and simple software, it causes particularly low production costs.

Profibus (Process Field Bus)

This standard for fieldbus communication in automation technology is used in the manufacturing industry for fast communication in machines and systems between sensors/actuators and controls 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 wiring harnesses and thereby save manufacturing costs and weight. CAN protocols have established themselves in many security-relevant areas, such as in the automotive industry, medical, aircraft and space travel and pyrotechnics, ship and rail vehicle construction, as well as in areas of automation technology.

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