3-1.c

本书是单片机系列教材

/*3-1.C*/
void sound(unsigned int freq);
main()
{
 unsigned int freq;
 do
{
 do 
 {
  freq=rand();
}while(freq>1000);
sound(freq);
}while(!kbhit());
}
void sound(unsigned int freq)
{
 unsigned i;
 union
 {
  long divisor;
  unsigned char c[2];
}count;
unsigned char bits;
count.divisor=119328/freq;
outportb(0x43,0xb6);
outportb(0x42,count.c[0]);
outportb(0x42,count.c[1]);
bits=inportb(0x61);
outportb(0x61,bits|3);
for(i=0;i<20000;i++);
outportb(0x61,bits&0xfc);
}