Keyboard Interfacing to 8051

  
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The key board here we are interfacing is a matrix keyboard. This key board is designed with a particular rows and columns. These rows and columns are connected to the microcontroller through its ports of the micro controller 8051. We normally use 8*8 matrix key board. So only two ports of 8051 can be easily connected to the rows and columns of the
Keyboard Interfacing to 8051 - schematic

key board. When ever a key is pressed, a row and a column gets shorted through that pressed key and all the other keys are left open. When a key is pressed only a bit in the port goes high. Which indicates microcontroller that the key is pressed. By this high on the bit key in the corresponding column is identified. Once we are sure that one of key in the key board is pressed next our aim is to identify that key. To do this we firstly check for particular row and then we check the corresponding column the key board. To check the row of the pressed key in the keyboard, one of the row is made high by making one of bit in the output port of 8051 high. This is done until the row is found out. Once we get the row next out job is to find out the column of the pressed key. The column is detected by contents in the input ports with the help of a counter. The content of the input port is rotated with carry until the carry bit is set. The contents of the counter is then compared and displayed in the display. This display is designed using a seven segment display and a BCD to seven segment decoder IC 7447. The 8051 has 4 I/O ports P0 to P3 each with 8 I/O pins, P0. 0 to P0. 7, P1. 0 to P1. 7, P2. 0 to P2. 7, P3. 0 to P3. 7. The one of the port P1 (it understood that P1 means P1. 0 to P1. 7) as an I/P port for microcontroller 8051, port P0 as an O/P port of microcontroller 8051 and port P2 is used for displaying the number of pressed...



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