/*------------------------------------------------------------------------------
HELLO.C

Copyright 1995-1999 Keil Software, Inc.
------------------------------------------------------------------------------*/

#include <REG52.H>                /* special function register declarations   */
                                  /* for the intended 8051 derivative         */

#include <stdio.h>                /* prototype declarations for I/O functions */
#include <stdlib.h>
#include <string.h>
#include <ABSACC.H>

#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                        */
char *gpch=100;
void chadr(char *chr)
{
 chr=gpch;
}
 void chva(char *chr)
 {
  *chr=20;
 }
/*---------------------------------------------
The main C function.  Program execution starts
here after stack initialization.
------------------------------------------------*/
void main (void) {
 char testchr=10;
/*------------------------------------------------
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        */
    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.
------------------------------------------------*/

 printf("init=%bd/n",testchr);
 chva(&testchr);//变量地址传入函数，函数直接对变量操作;而不是地址
 printf("after=%bd/n",testchr);
 chadr(&testchr);//地址传入函数后，存储在栈中，在函数中修改无效，返回消失，还是原来的地址
 printf("changeaddr=%bd/n",testchr);
  while (1) {
    P1 ^= 0x01;           /* Toggle P1.0 each time we print */

  }
}