I have a question:

In CPU's which have 256 bytes of internal RAM , what happens if SP goes past the address 7F ?

I checked that if SP is set at the end , and if functions are called in nested manner,then the SP continues to grow past 7F.
The 80h-FFh RAM array is indirectly addressable and SP is part of SFR's which are directly addressable? Maybe SP operations are done
inside cpu in the Indirect manner?

Is it true that it be possible to use part of upper memory 80h-FFh for SP array ?

Keil's compiler shows error if you compile for 8031 family and the SP goes past 7F, but if you choose 8032 it works.