我单片机数码管位码是0xfe,0xfd,0xfb,0xf7,0xef,0xdf,0xbf,0x7f,是共阳极的,按理说应该用共阳极的段码,可程序中却用的共阴极的段码,{0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f},请问这是为什么?