Warnning! Microcontroller 89C81RD2-IM by ATMEL has only 1024 Bytes XRAM. Do not set bit XRS2 in AUXR register with RTX51 Full. If you set this bit whitin program, is not perform correct.
"Please read datasheets carefully" He probably thinks he actually has the AT89C51RD2. Some of the Atmel made T89C51RD2 devices are badged "ATMEL 89C51RD2" giving the impression they are AT devices when they are actually T devices. Even the distributors don't seem to know the difference.