> The 89C51RX+ contains two special
> FLASH registers:the BOOT VECTOR and
> STATUS BYTE. I want to knew their
> address and how to change the
> registers.

AFAIK they haven't any addresses. Actually 89C51RX+ has three special (and not mentioned anywhere) SFRs to work with Flash. If you enable Boot ROM and read 1k of code at 0FC00h, and disassemble it, you'll see how it is done.

But I suggest you to not reinvent the wheel but to use these Flash functions in Boot ROM. There are also functions to handle Status Byte and Boot Vector. Look at the manual.

==
Tomas