XBYTE
The XBYTE macro allows you to access individual bytes in the external data
memory of the 8051. You may use this macro in your programs as follows:
rval = XBYTE [0x0002];
XBYTE [0x0002] = 57;
to read or write the contents of the byte in external data memory at address
0002h.
这个解释,你应该看得懂吧,已经说的很清楚了。楼主应该是在用KEIL编写C51的程序。
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现阶段连菜鸟都算不上,我就是来顶贴学习的。