Switch Debouncing Program

17 July 2011

2 min read

20746 views

Switch Interfacing & Debouncing

Over here we consider ONE Switch & TWO LED connected to a microcontroller. Please check the SWITCH INTERFACING and the LED INTERFACING article to see how to connect Switches & LED’s to a microcontroller.

Here is a program that will TURN ON A LED1 if a switch is debounced properly & will TOGGLE LED2 if there is some error in switch debouncing. LED1 will be ON until the switch is pressed & will turn OFF as soon as it’s released. We have taken the debounce period as 20ms. So once a LOW signal has been received from the switch the controller will again check the switch status after 20ms & if at that time the switch is high LED2 will be toggled and if the switch is LOW LED1 will be turned ON.


led1	bit	P2.0
led2	bit	P2.1
switch1	bit	P1.0


ORG 0000h
setb switch1	*//initialize switch 1 as input*
setb led1	*//Turn OFF LED1*
setb led2	*//Turn OFF LED2*

wait:
jb switch1,wait	*// Wait till switch1 has been pressed*
call debounce_delay jb switch1,c1_wait

//After debouncing period, switch is low hence switch succesfully debounced

*clr led1*	*//Turn ON LED1*
*jnb switch1,$*	*//wait till switch has been released*
*setb led1*	*//Turn OFF LED1*
*ajmp wai*t

*c1_wait:*
*//Switch PIN* *high after debounce period so error in debouncing*
cpl led2 ajmp wait

debounce_delay:	//Subroutine for generating 20ms delay
mov r7,#245
*l1_debounce_delay:* *mov r6,#40* *djnz r6,$* *djnz r7,l1_debounce_delay* *ret*
*END*

Switch Debouncing Program

17 July 2011

2 min read

20746 views

Switch Interfacing & Debouncing


led1	bit	P2.0
led2	bit	P2.1
switch1	bit	P1.0


ORG 0000h
setb switch1	*//initialize switch 1 as input*
setb led1	*//Turn OFF LED1*
setb led2	*//Turn OFF LED2*

wait:
jb switch1,wait	*// Wait till switch1 has been pressed*
call debounce_delay jb switch1,c1_wait

//After debouncing period, switch is low hence switch succesfully debounced

*clr led1*	*//Turn ON LED1*
*jnb switch1,$*	*//wait till switch has been released*
*setb led1*	*//Turn OFF LED1*
*ajmp wai*t

*c1_wait:*
*//Switch PIN* *high after debounce period so error in debouncing*
cpl led2 ajmp wait

debounce_delay:	//Subroutine for generating 20ms delay
mov r7,#245
*l1_debounce_delay:* *mov r6,#40* *djnz r6,$* *djnz r7,l1_debounce_delay* *ret*
*END*