Hello Friends,
Fast of all just introduction to :-
What is keyboard interfacing?
The method used to connect a keyboard to the main computer system is known as keyboard interfacing. Whenever a key is depressed and scan code is generated it is send to the processor via the keyboard interface. There are two types of interfaces :-
¤ Hardware Interface
¤ Software Interface
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¤ Hardware Interface :- The hardware interface includes the connection wire , socket and the plug. The wire is generally five to six feet long and is a coded wire. It connects the keyboard to the main system at back side at a small opening called socket. A connector called plug is used to connect the cable in socket.
The most common type of connector for keyboards is a 5 pin DIN connector , for PC's , while for mini systems like PS/2 It is 6 pin DIN connector. Though the shapes of these connectors is different even then the basic working of both of them along with carried signals are same.
All sort of connector use four conductor wires are used for carring various signals in the computer and one or two additional wires which are not used generally. The four wires in them are used for following purposes. One wire is used to carry serial format data to the computer. Second is used to send keyboard clock signal to synchronize the keyboard logic with that of the computer logic. Third wire is used as a return line for keyboard circuit and is generally grounded.
¤ Software Interface :- The keyboard microprocessor 8048 contains a small program which generates the scan codes for the key pressed. It also takes care of decouncing problems and repetition of keys. The program also contains instructions to store the generated scan codes into keyboard buffer memory and then it is made available to proper port so that BIOS can read it. The keyboard also generates an interrupt signal for main processor informing about the availability of scan code whenever the first key on keyboard is pressed. When the main processor receives this interrupt signal it makes an interrupt service routin (ISR) for making the keyboard active. The ISR reads scan code from keyboard buffer memory and then informs the keyboard that it can remove the code from the buffer.
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