Freely programmable Keyboard Controller

Item no. 1871

Published in Design & Elektronik

Description

Author: Dipl.-Phys. Gert Breidenbach
Universal, freely programmable keyboard controllers - the all-rounders
Industrial membrane keyboards
The use of PCs in industry for solving control tasks requires the connection of special key arrangements for operating the machines. Often different functions, e.g. for configuration and subsequent routine operation, are to be realized with the smallest possible number of keys in two levels. Of course, one wants to be able to use the standard connection options and keyboard drivers on the PC. In addition to the established PS/2 interface, the USB bus is becoming increasingly popular for keyboard functions. It is the coming, flexible single-cable connection to which several peripheral devices can be connected at the same time. For industrial keyboard applications, the production quantities are usually not high, so that the special integration of a keyboard controller with only one interface option does not seem very advisable. Also, a universally applicable controller can introduce a certain degree of hardware standardization when used in different projects. In this sense the separation of keyboard board and controller board has some advantages. GeBE takes these circumstances and the clearly recognizable trend towards the USB bus into account and offers the universally applicable keyboard controller series GCK-980 on the market. Essential features are the compatibility to PS/2, USB and ADB (Apple Macintosh), as well as the possibility to connect a trackball in addition to a key matrix and - when using the PS/2 interface - an additional PS/2 keyboard via an integrated switch. This article describes the functions of the freely programmable GeBE keyboard controllers and their various applications.
Clear structure
In 8 rows and 16 columns, from one to 128 keys can be connected directly PC-compatible to the host via the GCK-982 keyboard controller from GeBE (see Fig. 2 block connection). Practically all common metal as well as foil and conductive rubber contacts with contact resistances of less than 200 ohms can be used in the key matrix. The N-key rollover mode, in which keys pressed one after the other and then closed at the same time are all detected separately, is possible without interference by providing decoupling diodes to avoid shadow keys.
The "block key" enables a second, virtual key level
One of the connected keys can be declared as the so-called "block key". With the help of this key a second, virtual keyboard level is opened, so that practically with the same key arrangement two independent keyboards are represented. This is done exclusively by the software running on the keyboard controller. By pressing the block key, the controller switches to the other keyboard level. The keyboard driver in the host remains unaffected and interprets all signals sent over the interface as if they were coming from only one keyboard. Since the keyboard driver in the host assumes that a standard keyboard is connected, it should be noted that the multiple key assignments defined in the standard layout of a PC keyboard are also preserved in the freely programmable key layout -- i.e. also in the second block level. In this sense, the second keyboard level, which is accessible after the installation of the "block key", can also help to a certain extent to bypass this rigid assignment on a key without having to rewrite the keyboard driver in the PC.
Fully equipped controller for development
In the standard configuration available from GeBE, the GCK-982-USB-O-EVAL controller has a 99-pin male connector to which existing keyboard matrices with a wide variety of connector orientations -- rows and columns alternate with each other or are arranged in groups of columns and rows on the connecting cables -- can be clearly connected. Drivers for 3 LEDs to indicate the functions CAPS-LOCK, NUM-LOCK, SCROLL-LOCK are provided.
Free programmability with the help of a PC program
All keys on a standard PC keyboard, including those with special meaning, such as SHIFT, CONTROL, NUM-LOCK, RETURN, etc., can be freely selected in the key matrix. Programming is done with the help of a PC program via the USB interface in an EEPROM located on the controller. The table with the unique usage codes for USB corresponding to the key arrangement is generated on the PC. The controller takes the key coding valid for USB from the EEPROM table. If the controller is connected to the host via USB or a PS/2 or ADB interface (Apple), this is automatically detected by the controller. Then the determined USB usage codes are converted into the corresponding codings.
Helpful strings
Strings can also be stored on the key positions in such a way that keystroke sequences with up to 8 keystrokes can be sent with one keystroke. The programming procedures are described in detail in a comprehensive manual. To support the development GeBE supplies the PC program on diskette.
Archiving and downloading from PC, programming service
The keyboard programming once created can be archived in the PC and copied from there to further keyboard controllers during a series production. GeBE also offers its customers the complete programming service, so that only the desired matrix assignment has to be defined by the user. GeBE also uses the controllers in customer-specific applications and in its own product range.
Mouse functions
The hardware of the GCK-982 controller can be configured for two different cursor control functions, namely for a quadrature output (optical) trackball and a micro joystick (Versa Point). For USB and ADB applications, these functions are advantageously looped into the BUS connection as well, so that the controller with mouse replacement function is connected to the host via USB or ADB with only one cable. For conventional PCs the keyboard function of the controller is realized via a PS/2 cable and the mouse replacement function is connected either via a PS/2 connection cable or via a serial RS232 interface cable.
Switch
It is advantageous that the PS/2 keyboard interface additionally has a switch function. An additional connector can be used to connect a further, complete PS/2 keyboard, so that, for example, an extension with a separate numeric keypad is possible with the PS/2 version.
Other freely programmable keyboard controllers with teach-in
GeBE also offers the GCK-972 series of freely programmable keyboard controllers, which are mechanically compatible with the GCK-980 series. These controllers are prepared for the control of a PS/2 interface as well as for RS232 connection. Their advantage is the longer string length, which can be placed behind each key. Even programmable pauses can be inserted into the strings, which can be helpful for bridging program call times. Especially if you want to start and execute work with a single keystroke. In addition, the programming effort for these controllers is low because they have extensive help for programming. The implemented teach-in procedure simplifies the programming procedure considerably because special knowledge is not required to create the programming. The teach-in procedure relies only on the use of an additional standard PC keyboard. Also, the controllers are equipped with a stand-alone copying algorithm for duplicating the programming. For a more detailed description, see www.tastaturen.com.
GeBE customizes the hardware
If keyboards are required in certain mechanical forms or in larger quantities, it is possible to reduce the number of components to a minimum and to integrate the circuit directly into the keyboard board, on which the keys are also located. This is e.g. the case with the foil-covered industrial keyboard GFK-97 from GeBE, which is still mainly used with PS/2 connections, but on the other hand can also be supplied as a USB version without having to install any other hardware.

Freely programmable Keyboard Controller

Description

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