__IO_REG8_BIT( SYS,             0xFFFFF802, __READ_WRITE )

#define __IO_REG8_BIT(NAME, ADDRESS, ATTRIBUTE)                 \

                      __near __no_init volatile ATTRIBUTE union \

                        {                                       \

                          unsigned char NAME;                   \

                          __BITS8 NAME ## _bit;                 \ // ## _bit ?? ## 可以連線前後

                                                                               //比如 NAME 是 a，這句就//是    __BITS8   a_bit;

                        } @ ADDRESS;

typedef struct

{

    unsigned char no0:1;

    unsigned char no1:1;

    unsigned char no2:1;

    unsigned char no3:1;

    unsigned char no4:1;

    unsigned char no5:1;

    unsigned char no6:1;

    unsigned char no7:1;

} __BITS8;

__near

Syntax Follows the generic syntax rules for memory type attributes that can be used on data

objects, see Type attributes, page 193.

Description The __near memory attribute overrides the default storage of variables given by the

selected data model and places individual variables and constants in near memory. You

can also use the __near attribute to create a pointer explicitly pointing to an object

located in the near memory.

Storage information Address range: 0x0-07FFF and 0xFFFF8000-0xFFFFFFFF (64 Kbytes)

Example __near int x;

See also Memory types, page 13.

__no_init

Syntax Follows the generic syntax rules for object attributes, see Object attributes, page 195.

Description Use the __no_init keyword to place a data object in non-volatile memory. This means

that the initialization of the variable, for example at system startup, is suppressed.

Example __no_init int myarray[10];

#define PRERR             SYS_bit.no0

在stdbool.h中，定義了一個位巨集，如果需要變數定義，就是如下：
bool abit;
abit就是一個位變量了，這種方法簡單，但是在多個位的時候不好處理，比如需要一批位變數
初始化的時候。
還可以採用如下方法：
typedef struct
{
    unsigned char no0:1;
    unsigned char no1:1;
    unsigned char no2:1;
    unsigned char no3:1;
    unsigned char no4:1;
    unsigned char no5:1;
    unsigned char no6:1;
    unsigned char no7:1;
} __BIT8 ;
volatile union { unsigned char strack; __BIT8 strack_bit; } ;
union { unsigned char sk; __BIT8 sk_bit; } ;
定義位：
#define mflag        strack_bit.no0

volatile union { unsigned char strack; __BIT8 strack_bit; } ;
中加上VOLATILE，如果發現給編譯器優化掉，就一定要加上，
strack 就是一個可按位操作的變數，
strack=0;就可以把所有8個位全部清零，比起BOOL方便一些。