按键开关消抖程序

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：

led1bitP2.0
led2bitP2.1
switch1bitP1.0
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