When I use one 82c55. I can define as follow: #define D8255A XBYTE[0xeffc] #define D8255B XBYTE[0xeffd] #define D8255C XBYTE[0xeffe] #define C8255 XBYTE[0xefff] Now I need to use two chips of 82c55. And how can I to define their address? Thank U~