Just looking at 52 SCM and GPS communication program, see a function, absacc.h, seemingly never encountered, Baidu a bit, combined with their own understanding, sorted as follows: http://blog.sina.com.cn/s/blog_4__ function

Just looking at 52 SCM and GPS communication program, see a function, absacc.h, seemingly never encountered, Baidu a bit, combined with their own understanding, sorted as follows:

Http://blog.sina.com.cn/s/blog_4f8cdc9e0100g1qp.html "51 single chip microcomputer KEILC header document ABSACC.H function"

http://apps.hi.baidu.com/share/detail/716779 "Absacc.h Library Introduction"

Http://blog.sina.com.cn/s/blog_5f0187c50100e0nt.html the role of #include<absacc.h> (turn)

Just look at these few basic enough, should be able to understand what this document is:

In a program, use the macros defined in the #include<absacc.h> to access an absolute address, including:
CByte, Xbyte, Pword, Dbyte, Cword, Xword, Pbyte, DWORD

For example:
RVAL=CBYTE[0X0002]; point to 0002h Address of program memory
Rval=xword [0x0002]; 0004h address pointing to external RAM//word is a word, two bytes, so 0004h

#define COM8255 XBYTE[0X060FF]//After COM8255, single-chip port P0 and P2 joint output 0X060FF Absolute Physical address (address pointing to the 82c55 instruction register)
#define PA8255 XBYTE[0X000FF]//After PA8255, single-chip port P0 and P2 federated output 0X000FF Absolute Physical address (address to a group a port register of 82c55)
#define PB8255 XBYTE[0X020FF]//After PB8255, single-chip port P0 and P2 joint output 0X020FF Absolute Physical address (address to the B-group Port Register of 82c55)
#define PC8255 XBYTE[0X040FF]//After PC8255, single-chip port P0 and P2 joint output 0X040FF Absolute Physical address (address to the C-Group Port Register of 82c55)

Similarly, in the GPS and SCM Communication, the following macro definition is good to understand:

#define GPS_LG0 xbyte[0x0]
#define GPS_LG1 xbyte[0x1000]
#define GPS_LG2 xbyte[0x2000]
#define GPS_LG3 xbyte[0x3000]
#define GPS_LAT0 xbyte[0x4000]
#define GPS_LAT1 xbyte[0x5000]
#define GPS_LAT2 xbyte[0x6000]
#define GPS_LAT3 xbyte[0x7000]
#define UTC0 xbyte[0xc000]
#define UTC1 xbyte[0xd000]
#define UTC2 xbyte[0xe000]
#define UTC3 xbyte[0xf000]

#define Snum xbyte[0xa000]

is to use Xbyte to make the defined macro point to an actual physical address.

In Keil, you can see the definition of this file directly:

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