#this function will only work on 8051 @12MHz
unsigned int get_distance()
{
unsigned int time;
trig=1;trig=1;trig=1;trig=1;trig=1; // 5us /
TMOD=0x01; // 2us / use timer0 16 bit mode
TH0=0x00; // 1us / clear reg
TL0=0x00; // 1us / clear reg
trig=0; // 1us / Total(5+2+1+1+1)=10us
while(!echo); // Wait until echo beome high
TR0=1; // Start the Timer
while(echo); // Wait until echo become low
TR0=0; // Stop the timer
time=((TH0<<
+TL0)/58; // Load timer value to register. 58us per cm.
return time;
}