Hello, The datasheet of the P89C664 says that it has 2K of data ram "on chip". But how do i have to address that memory? Does that 2K memory behaves like a XRAM memory like the 8051 from intel, and do i have to address it with the next statements...or something else? #define PBYTE ((unsigned char volatile pdata *) 0) rval = PBYTE [0x0002]; PBYTE [0x0002] = 38; thanks and greetz