Ich habe es via google gefunden: in sfr_defs.h

Code:
#define _SFR_IO8(io_addr) ((io_addr) + __SFR_OFFSET)
#define _SFR_IO16(io_addr) ((io_addr) + __SFR_OFFSET)

#ifndef __SFR_OFFSET
/* Define as 0 before including this file for compatibility with old asm
   sources that don't subtract __SFR_OFFSET from symbolic I/O addresses.  */
#define __SFR_OFFSET 0x20
#endif
Kann dies bitte jemand erläutern? Wann muss ich __SFR_OFFSET als 0 setzen anstelle 0x20?