@ in C header file

Question

Reading a header file, which implements the mapping of I/O devices for a microcontroller, I stumbled about the following code snippet:

typedef union{
    unsigned char Byte; 
    struct
    {
         unsigned char BIT0          :1;
         unsigned char BIT1          :1; 
         ...
         unsigned char BIT7          :1;
    }Bits; 
}COP;

extern volatile COP _COP @(0x0000 + 0x000000006FUL); 

I cannot make any sense of the last line since I do not know the @ Operator.