The _at_ keyword is used to specify the address of the variable when defining the variable.
The following are examples of using the _at_ keyword:
struct link
{
struct link idata *next;
char code *test;
};
struct link list idata _at_ 0x40; /* Define the structure located at address 0x40 in the lower 128 bytes of the internal RAM*/
char xdata text[256] _at_ 0xE000; /* define the array at the external RAM 0xE000 address */
int xdata i1 _at_ 0x8000; /* define an integer variable located at the address 0x8000 in external RAM*/
volatile char xdata IO _at_ 0xFFE8; /* Define external IO with address 0xFFE8 */
char far ftext[256] _at_ 0x02E000; /* define the array at the external RAM 0x2E000 address */
void main ( void ) {
link.next = (void *) 0;
i1 = 0x1234;
text[0] = 'a';
IO = 6;
ftext[0] = 'f';
}
In a .c file, these variables are defined as above, and can be referenced in another .c file as follows:
struct link
{
struct link idata *next;
char code *test;
};
extern struct link idata list;
extern char xdata text[256];
extern int xdata i1;
extern volatile char xdata IO;
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