Interfacing Keyboard to 8051 Microcontroller
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 key board.
Whenever 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 BCD equivalent number of counter is sent through output part of 8051 displays the number of pressed key.
Program for Keyboard Interfacing with 8051
Program for Keyboard Interfacing with 8051
Start of main program:
to check that whether any key is pressed
start: mov a,#00h
mov p1,a ;making all rows of port p1 zero mov a,#0fh
mov p1,a ;making all rows of port p1 high
press: mov a,p2
jz press ;check until any key is pressed
after making sure that any key is pressed
mov a,#01h ;make one row high at a time mov r4,a
mov r3,#00h ;initiating counter
next: mov a,r4
mov p1,a ;making one row high at a time
mov a,p2 ;taking input from port A
jnz colscan ;after getting the row jump to check column
mov a,r4
rl a ;rotate left to check next row
mov r4,a
mov a,r3
add a,#08h ;increment counter by 08 count
mov r3,a
sjmp next ;jump to check next row
after identifying the row to check the colomn following steps are followed
colscan:mov r5,#00h
in: rrc a ;rotate right with carry until get the carry
jc out ;jump on getting carry
inc r3 ;increment one count
jmp in
out: mov a,r3
da a ;decimal adjust the contents of counter before display
mov p2,a
jmp start ;repeat for check next key
Seven Segment Disply Interfacing with 8051
