”即可使用其中定义的宏来访问绝对地址，包括：

CBYTE、XBYTE、PWORD、DBYTE、CWORD、XWORD、PBYTE、DWORD

具体使用可看一看absacc.h便知

例如：

＃include#define ADstart  XBYTE[0x8000]        //总线方式访问AD

#define ADL     XBYTE[0x8000]

#define ADH     XBYTE[0x8001]

rval=CBYTE[0x0002];指向程序存贮器的0002h地址

rval=XWORD [0x0002];指向外RAM的0004h地址

2. _at_关键字

直接在数据定义后加上_at_ const即可，但是注意：

(1)绝对变量不能被初使化；

(2)bit型函数及变量不能用_at_指定。

例如：

idata struct link list _at_ 0x40;指定list结构从40h开始。

xdata char text[25b] _at_0xE000；指定text数组从0E000H开始

提示：如果外部绝对变量是I/O端口等可自行变化数据，需要使用volatile关键字进行描述，请参考absacc.h。

3. 连接定位控制

此法是利用连接控制指令code xdata pdata data bdata对“段”地址进行，如要指定某具体变量地址，则很有局限性，不作详细讨论。

附:(c51)

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

ABSACC.H

Direct access to 8051, extended 8051 and Philips 80C51MX memory areas.

Copyright (c) 1988-2002 Keil Elektronik GmbH and Keil Software, Inc.

All rights reserved.

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

#ifndef __ABSACC_H__

#define __ABSACC_H__

#define CBYTE ((unsigned char volatile code *) 0)

#define DBYTE ((unsigned char volatile data *) 0)

#define PBYTE ((unsigned char volatile pdata *) 0)

#define XBYTE ((unsigned char volatile xdata *) 0)

#define CWORD ((unsigned int volatile code *) 0)

#define DWORD ((unsigned int volatile data *) 0)

#define PWORD ((unsigned int volatile pdata *) 0)

#define XWORD ((unsigned int volatile xdata *) 0)

#ifdef __CX51__

#define FVAR(object, addr) (*((object volatile far *) (addr)))

#define FARRAY(object, base) ((object volatile far *) (base))

#define FCVAR(object, addr) (*((object const far *) (addr)))

#define FCARRAY(object, base) ((object const far *) (base))

#else

#define FVAR(object, addr) (*((object volatile far *) ((addr)+0x10000L)))

#define FCVAR(object, addr) (*((object const far *) ((addr)+0x810000L)))

#define FARRAY(object, base) ((object volatile far *) ((base)+0x10000L))

#define FCARRAY(object, base) ((object const far *) ((base)+0x810000L))

#endif

#endif

附:(c166)

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

ABSACC.H

Direct access to 166 memory areas for C166/EC++ Version 5.

Copyright (c) 1992-2004 Keil Elektronik GmbH and Keil Software, Inc.

All rights reserved.

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

#ifndef __ABSACC_H__

#define __ABSACC_H__

#if (__MODEL__ == 0)

#define MVAR(object, addr) (*((object volatile *) (addr)))

#define MARRAY(object, base) ((object volatile *) (base))

#else

#define MVAR(object, addr) (*((object volatile far *) (addr)))

#define MARRAY(object, base) ((object volatile far *) (base))

#define HVAR(object, addr) (*((object volatile huge *) (addr)))

#define HARRAY(object, base) ((object volatile huge *) (base))

#define XVAR(object, addr) (*((object volatile xhuge *) (addr)))

#define XARRAY(object, base) ((object volatile xhuge *) (base))

#endif

#endif