Technical article: PC keyboard controller freely programmable via teach-in

Item no. 1884

Published in Elektronik Praxis

Description

Freely programmable keyboard controller
Author: Dipl. Physiker Gert Breidenbach is Head of Marketing and Development at GeBE Elektronik und Feinwerktechnik GmbH in Germering near Munich.
The ever-increasing use of PCs to solve control tasks in industry requires the adaptation of special keyboard arrangements to operate the controlled machines. In doing so, one would like to be able to fall back on the standard keyboard driver in the PC as far as possible. The GCK-972-PS/2 keyboard controller from GeBE described below, which is freely programmable via an easy-to-use teach-in procedure, is particularly suitable for this purpose.
Clear matrix structure
In a matrix of 8 rows and 16 columns, up to 128 keys can be connected directly to the GCK-972-PS/2 keyboard controller from GeBE (see block diagram). Practically all common keys as well as foil and conductive rubber contacts can be used. Shadow keys can be avoided via decoupling diodes, which then also enables the N-key rollover mode without interference.
Two virtual key levels -- the "block key" makes it possible.
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 keys two independent keyboards are represented. This is done exclusively by the software of the keyboard controller. By pressing the block key -- a toggle mode can also be selected -- the controller switches to the second keyboard level. The keyboard driver in the PC remains unaffected and interprets all signals sent via the PS/2 interface as if they came from only one keyboard. Since the keyboard driver in the PC assumes that a standard keyboard is connected to the PS/2 keyboard port, please note that the keyboard driver in the Since the keyboard driver in the PC assumes that a standard keyboard is connected to the PS/2 keyboard port, it should be noted that the multiple assignments of a key that can be reached via the special keys are also assigned to the same key of the freely programmable keyboard. In this sense, the second keyboard level, which can be reached after setting up the "block key", can also help to a certain extent to circumvent this rigid assignment without having to rewrite the keyboard driver in the PC.
Free programmability
Each of the keys is freely programmable by the user without any restriction. All keys on a standard PS/2 keyboard, even those with special meaning, such as SHIFT, CONTROL, NUM-LOCK, RETURN, etc., can be freely selected in the matrix in a teach-in procedure. All MF2 scancodes Set II or III are output via the PS/2 interface and all known MF2 keyboard system commands are processed. The assignment of Windows95 keys is also possible.
Programming without PC program - with a simple teach-in keyboard
A PC keyboard equipped with code set 3 is connected via the integrated switch, via which another PC keyboard can be looped through to the keyboard port of the PC in normal operation, with the aid of which the controller is programmed in an easy-to-use teach-in algorithm. The controller is equipped with an acoustic signal generator which, together with the connectable LEDs, serves for orientation when running through the programming algorithm. When the 5V power supply is switched on, the controller with connected key matrix is controlled into the teach-in mode by means of the programming mode key. Now a certain key is selected by keys on the keyboard to be programmed. The controller confirms the selection via the LEDs. It now expects the desired key to be pressed on the teach-in keyboard connected to the turnout and again acknowledges this by corresponding flashing of the LEDs. Now a next key can be selected and a key function assigned to it via the teach-in keyboard and so on. The programming of the keys is permanently stored in an EEPROM of the controller.
Helpful strings - even with pause
If several keys are pressed in succession on the teach-in keyboard instead of just one, the complete key sequence is stored and output later as a so-called string when this key is pressed. These strings can also be interrupted by a programmable pause in their length. Thus a whole key sequence can be sent first with a keystroke, e.g. for calling a special program. During the programmed pause the program can start safely. Then the second part of the string can e.g. trigger a certain function in the program. The string length of each key is limited to 30 bytes.
Duplicate programming
- Directly from the master keyboard Once the special keyboard has been programmed, it can be used as a master in a copy process. Via a download algorithm, the keyboard controller to be programmed copies itself the programming for its EEPROM from the master keyboard connected to its switch, without a keyboard matrix having to be connected. - Archiving and downloading from PC With a program developed by GeBE, the keyboard programming once created can also be archived in the PC and from there in turn copied to further keyboard controllers by a down-load procedure.
A beginner's set makes it easier to get started with the teach-in process
This archiving program is part of a beginner's set (see picture), which contains a freely programmable controller GCK-972-PS/2-EVAL and a self-labelled membrane keyboard as a 16-key matrix for training purposes, in addition to the required teach-in keyboard. A small control panel with indicator LEDs and mode button can be used to select the programming. In the detailed manual, help tables are provided, which cleverly support the use of the controller, especially with complicated key arrangements.
Hardware and software can be extended customer-specific
In the standard configuration available from stock at GeBE, the controller has a 99-pin male connector to which already existing keyboard matrices with different orientation of the connections -- rows and columns alternate with each other or are arranged in groups of columns and rows on the connection cables -- can be clearly connected. In its standard configuration, GeBE's GCK-972-PS/2 keypad controller has drivers for 4 LEDs to indicate the CAPS-LOCK, NUM-LOCK, SCROLL-LOCK and BLOCK functions. A key switch, which is independent of the key matrix, provides a lock-off possibility. Furthermore, a power-down power saving mode with sleep function can be supported via a wake-up logic. An integrated watchdog increases the interference immunity of the controller. The single chip µ-processor used in the controller has a flash memory, so that a program update is possible at any time. On the controller board some functions are already provided, which are not equipped in the standard version. For example, an RS232 and an SPI interface can also be installed, which can be used to connect peripheral devices such as mouse functions, barcode or card readers and ID devices if the appropriate special programming is carried out.
Freely programmable controller with serial RS232 interface
In the same layout the freely programmable keyboard controller GCK-972-RS232 equipped with serial interface is available. In contrast to the key codes of the PS/2 controller, this sends out single characters or even whole strings already encoded in ASCII code via the serial RS232 interface when a key is pressed. It can be programmed just as easily with a teach-in procedure as the freely programmable PS/2 keyboard controller described in detail above.

Technical article: PC keyboard controller freely programmable via teach-in

Description

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Freely programmable Keyboard Controller