Description
| Please click on the pdf below: Technical article: Keyboards with programmable display | |
| The idea of building a display into a keyboard is not new. As a rule, they become simple terminals. The display provides a minimum of feedback for the operator. Examples are the display in the PIN pad during a payment process or the status display in laptops that shows important additional information. | |
| Unfortunately, this useful feature often falls victim to the red pen. Mostly, the display is degraded to simple LED indicators. This is understandable, because another interface to the display (e.g. RS232) is needed, including the entire control. Wouldn't it be desirable to control the display via the existing PS/2 or USB keyboard interface without additional electronics? For compatibility reasons, it should also be possible to use the standard keyboard driver. All this has been realised in the GCK-978 keyboard controller. Translated with www.DeepL.com/Translator (free version) | |
| Hardware | |
| The functional units of the GCK-978 keyboard controller are modular. The main processor communicates with the host computer via the PS/2 or USB keyboard interfaces. Keyboard-internal function units are connected to the main processor via an internal I2C bus system. Another processor, the scan engine, manages the scanning of up to 160 keys. The number of keys can be increased by cascading several scan engines. A three-track magnetic card reader is another available function unit in the GCK-978. Many commercially available I2C displays can now be connected to this internal bus without further electronics. I2C displays are available as text, graphic or segment displays. Translated with www.DeepL.com/Translator (free version) | |
| Software | |
| With a USB or PS/2 keyboard interface, one data direction is used to transmit the key data, the other to transmit control commands to the keyboard, e.g. switching the LEDs on/off. Other data in the direction of the keyboard is not provided. In the GCK-978 solution, the display data is transmitted transparently to the display via this channel in addition to the control commands. The transparent transmission allows the use of practically all I2C displays, as the display data ultimately remain unchanged. With the help of a specially developed communication protocol between keyboard and PC, the keyboard processor can recognise whether the incoming byte is a control command for the keyboard or a display data. This means that a keyboard control command can be transmitted even during a data transmission to the display. Translated with www.DeepL.com/Translator (free version) | |
| Driver | |
| How do you actually control such a display on a PC? In PS/2 mode, the simplest method would be to pass the display data directly to the keyboard port. However, this data would not be synchronised with the keyboard driver control commands. A data conflict would be pre-programmed. It is better to write a new keyboard driver with all the extension functions that one wants. However, the effort would be enormous. | |
| The solution for the GCK-978 is a special filter driver that hooks in between the port and the standard keyboard driver. It does not matter whether the PS/2 or USB interface is used. The filter driver forwards the keyboard data transparently and sends synchronised display data to the keyboard. The display data is automatically converted into the communication protocol in the filter driver, invisible to the user. The programmer only has to pass the display data and commands to the filter driver. The filter driver is installed once in the PC and is immediately ready for operation after a restart. Standard keyboards thus remain functional unchanged, as no new keyboard driver has been installed. |
Downloads
Fachartikel_Tastaturen mit programmierbarem Display_08_2007.pdf ↓
Fachartikel: Tastaturen mit programmierbarem Display
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