功夫不负有心人，找到了一些官方的8051例子

/*---------------------------------------------------------

---------------------------------------------------------*/

#include <reg52.h>

#include <stdio.h>



/*---------------------------------------------------------

Timer 0 Overflow Interrupt

---------------------------------------------------------*/

unsigned int T0_ISR_count = 0;



void T0_ISR (void) interrupt 1

{

T0_ISR_count++;

TF0 = 0;                        // Reset the interrupt request

}





/*---------------------------------------------------------

MAIN C function

---------------------------------------------------------*/

void main (void)

{

/*--------------------------------------

Set serial port for 9600 baud at

11.0592 MHz.  Note that we use Timer 1

for the baud rate generator.

--------------------------------------*/

SCON  = 0x50;

TMOD |= 0x20;

TH1   = 0xFA;

TR1   = 1;

TI    = 1;

PCON |= 0x80;



printf ("\nPulse Width Example Program\n\n");



/*--------------------------------------

Enable interrupts for timer 0.

--------------------------------------*/

ET0 = 1;

EA = 1;



/*--------------------------------------

Set Timer0 for 16-bit interval timer

mode.

--------------------------------------*/

TMOD = (TMOD & 0xF0) | 0x09;



while (1)

  {

/*--------------------------------------

Clear the timer overflow counter and

the timer low and high registers.  Then,

start the timer.

--------------------------------------*/

  T0_ISR_count = 0;

  TH0 = 0;

  TL0 = 0;



  TR0 = 1;



  printf ("\nStart a pulse.\n");



/*--------------------------------------

Wait for the pulse to start.

Then, wait for the pulse to end.

--------------------------------------*/

  while (!INT0);

  while (INT0);



/*--------------------------------------

Compute the width of the pulse -- one

clock cycle is 1us for a standard 8051

and display it.

--------------------------------------*/

  printf ("The width pulse is: %ld uSec\n",

          (unsigned long)((TH0 << 8) | TL0 | ((unsigned long)T0_ISR_count << 16)));

  }

}



/*---------------------------------------------------------

---------------------------------------------------------*/