PIC的程序疑惑
extern volatile unsigned int PORTB __attribute__((__sfr__));typedef struct tagPORTBBITS {
unsigned RB0:1;
unsigned RB1:1;
unsigned RB2:1;
unsigned RB3:1;
unsigned RB4:1;
unsigned RB5:1;
unsigned RB6:1;
unsigned RB7:1;
unsigned :4;
unsigned RB12:1;
unsigned RB13:1;
unsigned RB14:1;
unsigned RB15:1;
} PORTBBITS;
不知该格式的含义，((__sfr__))指代什么，求指导
