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using idata

hardian suprapto

i tried to make a space but it's still said "missing ';' before '_at_'"
i wrote :
char idata nim[14] _at_ 0x00;

and is idata starting address at 0x80?
and data starting address at 0x00?

so, if i want to set an array starting at the first address of idata, is it right if i define the array as idata and starting address at 0x00?

or i should starting at 0x80?

thanks very much

sincerly,
hardian

  • 0

    I created the following program:

    char idata nim[14] _at_ 0x00;

void main (void)
{
}

    And compiled it with no errors. The following listing file was generated:

    C51 COMPILER V6.10  TEST                                                                   01/26/2001 19:19:14 PAGE 1   


C51 COMPILER V6.10, COMPILATION OF MODULE TEST
OBJECT MODULE PLACED IN .\test.OBJ
COMPILER INVOKED BY: C:\Keil\C51\BIN\C51.EXE .\test.c DEBUG OBJECTEXTEND CODE SYMBOLS

stmt level    source

   1          char idata nim[14] _at_ 0x00;
   2          
   3          void main (void)
   4          {
   5   1      }
   6          
C51 COMPILER V6.10  TEST                                                                   01/26/2001 19:19:14 PAGE 2   

ASSEMBLY LISTING OF GENERATED OBJECT CODE


             ; FUNCTION main (BEGIN)
                                           ; SOURCE LINE # 3
                                           ; SOURCE LINE # 4
                                           ; SOURCE LINE # 5
0000 22                RET     
             ; FUNCTION main (END)

C51 COMPILER V6.10  TEST                                                                   01/26/2001 19:19:14 PAGE 3   

NAME                                    CLASS   MSPACE  TYPE    OFFSET  SIZE
====                                    =====   ======  ====    ======  ====


main . . . . . . . . . . . . . . . . .  PUBLIC   CODE   PROC     0000H  -----
nim. . . . . . . . . . . . . . . . . .  PUBLIC   IDATA  ARRAY    0000H  14


MODULE INFORMATION:   STATIC OVERLAYABLE
   CODE SIZE        =      1    ----
   CONSTANT SIZE    =   ----    ----
   XDATA SIZE       =   ----    ----
   PDATA SIZE       =   ----    ----
   DATA SIZE        =   ----    ----
   IDATA SIZE       =   ----    ----
   BIT SIZE         =   ----    ----
END OF MODULE INFORMATION.


C51 COMPILATION COMPLETE.  0 WARNING(S),  0 ERROR(S)

    Jon

  • 0


    The problem with the line below:

    char idata nim[14] _at_ 0x00;

    is the absolte setting to 0x00. Address 0 is the location of bank 0 registers in the 8051. You cannot use this as an absolute location.

    If you want the array to be in idata, all you need is:
    char idata nim[14];

    The linker will place this in the idata space. If you must have this array at absolute address 0x80, then:

    char idata nim[14] _at_ 0x80;

    will place the array at absolute address 80h. You should only use absolute addressing when you need to access external memory or memory mapped peripherals.

  • 0 in reply to Thomas Mazowiesky

    You should only use absolute addressing when you need to access external memory

    In general, you wouldn't need it for external memory (XDATA).

    Only use it if there's a specific reason why something has to be at a specific, fixed address location.

    otherwise, let the compiler sort out the allocation of variables in the available memory space.