DTMF(Dual-tone multi-frequency signaling )

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Dual-tone multi-frequency signaling

Dual-tone multi-frequency signaling is an in-band telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers.

#include

void main()
{
char a;
P1=0x0f;
P2=0x00;
while(1)
{
a=P1;
a=a&0x0f;
switch(a)
{
case 1: P2=0xff;
break;
case 2: P2=0x02;
break;
case 3: P2=0x03;
break;
case 4: P2=0x04;
break;
case 5: P2=0x05;
break;
case 6: P2=0x06;
break;
default:
P2=0x00;
}
}
}

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