Home | | Microprocessors and Microcontrollers | Interfacing and Program for Keyboard to 8051 Microcontroller

Chapter: Microprocessor and Microcontroller - Micro Controller Programming & Applications

| Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail |

Interfacing and Program for 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.

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






Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail


Copyright © 2018-2020 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.