#include "reg51.h"

#include "sio.h"



sbit TRIG = P2^7;

sbit ECHO = P2^6;



#define XTAL 19660800L

#define PERIOD12MS (12L * XTAL / 12L / 256L / 1000L)



void delay(unsigned int t)

{

    while(t--) ;

}



void main (void)

{   

    EA = 0;



    TMOD &= ~0x0F;      // clear timer 0 mode bits

    TMOD |= 0x01;       // put timer 0 into MODE 1, 16bit



    com_initialize ();    /* initialize interrupt driven serial I/O */

    com_baudrate (14400); /* setup for 14400 baud */





    EA = 1;                         // Enable Interrupts



    while (1)

    {

START:



        TR0 = 0;

        TH0 = 0;

        TL0 = 0;



        TRIG = 0;    //

        delay(100);

        TRIG = 1;    //

        TR0 = 1;     //

        while (ECHO) //

        {

            if (TH0 >= PERIOD12MS)  //

                goto START; 

        }

        TR0 = 0;    //

        com_putchar(TH0);  //

        com_putchar(TL0);

        TR0 = 1;

        while (TH0 < PERIOD12MS) ;  //

    }

}