/*------------------------------------------------------------------------------
HELLO.C
Copyright 1995-2005 Keil Software, Inc.
------------------------------------------------------------------------------*/
#include <REG52.H>                /* special function register declarations  */
                                  /* for the intended 8051 derivative        */
#include <stdio.h>                /* prototype declarations for I/O functions */
#ifdef MONITOR51                        /* Debugging with Monitor-51 needs  */
char code reserve [3] _at_ 0x23;        /* space for serial interrupt if    */
#endif                                  /* Stop Exection with Serial Intr.  */
                                        /* is enabled                        */
/*------------------------------------------------
The main C function.  Program execution starts
here after stack initialization.
------------------------------------------------*/
void main (void) {
/*------------------------------------------------
Setup the serial port for 1200 baud at 16MHz.
------------------------------------------------*/
#ifndef MONITOR51
    SCON  = 0x50;                /* SCON: mode 1, 8-bit UART, enable rcvr      */
    TMOD |= 0x20;              /* TMOD: timer 1, mode 2, 8-bit reload        */
system的头文件    TH1  = 221;                /* TH1:  reload value for 1200 baud @ 16MHz  */
    TR1  = 1;                  /* TR1:  timer 1 run                          */
    TI    = 1;                  /* TI:  set TI to send first char of UART    */
#endif
/*------------------------------------------------
Note that an embedded program never exits (because
there is no operating system to return to).  It
must loop and execute forever.
------------------------------------------------*/
  while (1) {
    P1 ^= 0x01;                /* Toggle P1.0 each time we print */
    printf ("Hello World\n");  /* Print "Hello World" */
  }
}

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