unsigned int data ABC _at_ 0x0028;
unsigned int data CBA _at_ 0x002A;
unsigned int data *Port _at_ 0x002C;

#include <at89x51.h>
#include <stdio.h>

void main(void)
{
	SCON = 0x50; //串口方式1,允許接收
	TMOD = 0x20; //定時器1定時方式2
	TH1 = 0xE8;	//11.0592MHz 1200波特率
	TL1 = 0xE8;
	TI = 1;
	TR1 = 1; //啟動定時器

	ABC = 10; //設初值
	CBA = 20;

	Port = &CBA; //取CBA的地址放到指針變量Port
	*Port = 100; //更改指針變量Port所指向的地址的內容

	printf("1: CBA=%d\n",CBA); //顯示此時CBA的值

	Port = &ABC; //取ABC的地址放到指針變量Port
	CBA	= *Port; //把當前Port所指的地址的內容賦給變量CBA

	printf("2: CBA=%d\n",CBA); //顯示此時CBA的值
	printf("   ABC=%d\n",ABC); //顯示ABC的值
}