实践中,单片机端口在连接开关器件时都要考虑消抖的问题,或在硬件上增加延迟,或是增加软件延迟查询的功能模块。这里,我们考虑这样一个检测电路:单片机连接一个开关和两个LED。程序是这样的,如果开关的消抖正确,就点亮LED1,否则就闪亮LED2。按下开关,点亮LED1,释放开关,LED1即熄灭。我们加入20毫秒的消抖延迟时间。当检测到开关为低电平时,单片机在延迟20毫秒后再次检测开关的状态。如果此时开关状态为高,则LED2就闪亮,如为低则点亮LED1。
源代码:
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
//switch low even after debouncing period
//switch has been succesfully debounced
clr led1 //Turn ON LED1
jnb switch1,$ //wait till switch has been released
setb led1 //Turn OFF LED1
ajmp wait
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