# include & ltreg 5 1 . h & gt；
# Define uchar unsigned characters
# Define uint unsigned integer
uint p = 0； //must be a uint definition (p is 2 bytes).
sbit k=p 1^7； //key
sbit doorbell=p3^0； //doorbell
Unsigned int I；;
void main()
{
Doorbell = 0;
TMOD = 0x 00；
TH0 =(8 192-700)/32； //700us timing
TL0 =(8 192-700)% 32；
IE = 0x82
while( 1)
{
If(K==0)// key to start the timer.
{
for(I = 0； I<2; I want to "Ding Dong" twice, but I can only "Ding Dong" once.
{
TR0 = 1；
while(TR0)；
}
}
}
}
Invalid timer 0 () interrupt 1
{
Doorbell = ~ doorbell;
p++；
If (p & lt600) // If you need to lengthen the sound, you can adjust it to 400,800.
{
TH0 =(8 192-700)/32； //700us timing
TL0 =(8 192-700)% 32；
}
else if(p & lt； 1200)
{
TH0 =(8 192- 1000)/32； // 1 millisecond timing
TL0 =(8 192- 1000)% 32；
}
other
{
TR0 = 0；
p = 0；
}
}