The

[chandrasekhar]

The subroutine check_keypad can be used to directly interface any 4X3 matrix keypad. It checks if any switch on the matrix keypad is pressed. If any of the switch is pressed then the switch is debounced and we wait until the switch has been released. Once the switch has been released the switch number is loaded into the accumulator and the carry flag is set to indicate that a switch has been pressed. If NO switch has been pressed then the accumulator is cleared and the carry flag is also cleared to indicate no switch has been pressed.

column1 bit P1.0 column2 bit P1.1 column3 bit P1.2       row1 bit P1.3 row2 bit P1.4 row3 bit P1.5       row4 bit P1.6 check_keypad:   clr column1   setb column2 ;Select Column 1 setb column3       jnb row1,c1_check_keypad jnb row2,c2_check_keypad jnb row3,c3_check_keypad jnb row4,c4_check_keypad       setb column1   clr column2 ;Select Column 2 setb column3       jnb row1,c5_check_keypad jnb row2,c6_check_keypad jnb row3,c7_check_keypad jnb row4,c8_check_keypad     setb column1   setb column2 ;Select Column 3 clr column3       jnb row1,c9_check_keypad jnb row2,c10_check_keypad jnb row3,c11_check_keypad jnb row4,c12_check_keypad     setb column1 setb column2 setb column3     mov a,#00h ;Since no switch has been pressed so Acc=00h clr c ;and C=0 ret       c1_check_keypad: //column 1, row 1 mov r7,#00h       deb1_check_keypad: ;debounce row 1 switch jb row1,r1_check_keypad djnz r7,deb1_check_keypad       jnb row1,$ ;wait till switch is released mov a,#1 ;since switch pressed is 1, Acc =1 setb c ;Indicating switch has been pressed setb column1   ret       r1_check_keypad:   setb column1 ;Error while debouncing so return mov a,#0 clr c ret     c2_check_keypad: //column 1, row2 mov r7,#00h       deb2_check_keypad: ;debounce row 2 switch jb row2,r2_check_keypad djnz r7,deb2_check_keypad       jnb row2,$ ;wait till switch is released mov a,#4 ;since switch pressed is 4, Acc =4 setb c ;Indicating switch has been pressed setb column1   ret       r2_check_keypad:   setb column1 ;Error while debouncing so return mov a,#0 clr c ret       c3_check_keypad: //column 1, row3 mov r7,#00h       deb3_check_keypad: ;debounce row 3 switch jb row3,r3_check_keypad djnz r7,deb3_check_keypad   jnb row3,$                                                     ;wait till switch is released mov a,#7                                                      ;since switch pressed is 7, Acc =7 setb c                                                            ;Indicating switch has been pressed setb column1 ret   r3_check_keypad: setb column1                                             ;Error while debouncing so return mov a,#0 clr c ret c4_check_keypad:                                             //column 1, row4 mov r7,#00h   deb4_check_keypad:                                       ;debounce row 4 switch jb row4,r4_check_keypad djnz r7,deb4_check_keypad jnb row4,$                                                ;wait till switch is released mov a,#10                                               ;since switch pressed is 10, Acc =10 setb c                                                       ;Indicating switch has been pressed setb column1 ret   r4_check_keypad: setb column1                                       ;Error while debouncing so return mov a,#0 clr c ret c5_check_keypad:                                            //column 2, row 1 mov r7,#00h   deb5_check_keypad:                                        ;debounce row 1 switch jb row1,r5_check_keypad djnz r7,deb5_check_keypad jnb row1,$                                                 ;wait till switch is released mov a,#2                                                  ;since switch pressed is 2, Acc =2 setb c                                                        ;Indicating switch has been pressed setb column2 ret   r5_check_keypad: setb column2                                          ;Error while debouncing so return mov a,#0 clr c ret c6_check_keypad:                                          //column 2, row2 mov r7,#00h   deb6_check_keypad:                                    ;debounce row 2 switch jb row2,r6_check_keypad djnz r7,deb6_check_keypad jnb row2,$                                            ;wait till switch is released mov a,#5                                             ;since switch pressed is 5, Acc =5 setb c                                                   ;Indicating switch has been pressed setb column2 ret   r6_check_keypad: setb column2                                   ;Error while debouncing so return mov a,#0 clr c ret c7_check_keypad:                                   //column 2, row3 mov r7,#00h   deb7_check_keypad:                              ;debounce row 3 switch jb row3,r7_check_keypad djnz r7,deb7_check_keypad jnb row3,$                                          ;wait till switch is released mov a,#8                                           ;since switch pressed is 8, Acc =8 setb c                                                 ;Indicating switch has been pressed setb column2 ret   r7_check_keypad: setb column2                                    ;Error while debouncing so return mov a,#0 clr c ret c8_check_keypad:                                     //column 2, row4 mov r7,#00h   deb8_check_keypad:                                ;debounce row 4 switch jb row4,r8_check_keypad djnz r7,deb4_check_keypad jnb row4,$                                          ;wait till switch is released mov a,#11                                         ;since switch pressed is 11, Acc =11 setb c                                                 ;Indicating switch has been pressed setb column2 ret   r8_check_keypad: setb column2                                    ;Error while debouncing so return mov a,#0 clr c ret c9_check_keypad:                                    //column 3, row 1 mov r7,#00h   deb9_check_keypad:                              ;debounce row 1 switch jb row1,r9_check_keypad djnz r7,deb9_check_keypad jnb row1,$                                         ;wait till switch is released mov a,#3                                           ;since switch pressed is 3, Acc setb c                                                 ;Indicating switch has been pressed setb column3 ret   r9_check_keypad: setb column3                                    ;Error while debouncing so return mov a,#0 clr c ret c10_check_keypad:                                   //column 3, row2 mov r7,#00h   deb10_check_keypad:                             ;debounce row 2 switch jb row2,r10_check_keypad djnz r7,deb10_check_keypad jnb row2,$                                          ;wait till switch is released mov a,#6                                           ;since switch pressed is 6, Acc =6 setb c                                                 ;Indicating switch has been pressed setb column3 ret   r10_check_keypad: setb column3                                    ;Error while debouncing so return mov a,#0 clr c ret c11_check_keypad:                                   //column 3, row3 mov r7,#00h   deb11_check_keypad:                              ;debounce row 3 switch jb row3,r11_check_keypad djnz r7,deb11_check_keypad jnb row3,$                                          ;wait till switch is released mov a,#9                                           ;since switch pressed is 9, Acc =9 setb c                                                 ;Indicating switch has been pressed setb column3 ret   r11_check_keypad: setb column3                                    ;Error while debouncing so return mov a,#0 clr c ret c12_check_keypad:                                 //column 3, row4 mov r7,#00h   deb12_check_keypad:                           ;debounce row 4 switch jb row4,r12_check_keypad djnz r7,deb12_check_keypad jnb row4,$                                          ;wait till switch is released mov a,#12                                         ;since switch pressed is 12, Acc =12 setb c                                                 ;Indicating switch has been pressed setb column3 ret   r12_check_keypad: setb column3                                    ;Error while debouncing so return mov a,#0 clr c ret