Dear Sir, I have used 89C52 with 113 bytes external memory of RTC. The R2 port context is changed when accessing to external memory. Is possible to access external memory using R0 or R1 instead DPTR? How to configure UV2 and startup files? Regards.
Access with the 8051 indirect addressing mode through R0 / R1 is known as the "pdata" memory space. Check the manual for declaring variables as pdata, and see the STARTUP.A51 file for configuring the memory areas for your system. Note that when the 8051 does an indirect access, P2 supplies the upper bits of the memory address