Apparently back in the 80's I learned that the only safe RAM area to read and write from, and use as standard "scratch pad" memory was from 30H to 7FH. Beyond those bounds you were corrupting either the stack or register banks, or SFR's. This was on the 8031 where external memory reigned supreme in designs. If you wanted RAM you used a separate RAM chip with a battery for storage (or a very expensive super-cap).

I am using the AT89LP4052 in this design and a EEPROM for storage of values
set into a RTC and changed once a month. The EEPROM is read only once during power up and these values are loaded into RAM for manipulation. A request to expand the features of this design have forced me to look for more internal RAM, otherwise the EEPROM gets read and written to once a minute - watching for alarm trigger points - and it's R/W life cycle would end quickly. Easier to load the trigger points into internal RAM and only R/W the EEPROM upon power up or value change. The customer didn't want to use a FRAM as it increased the cost of the design's component cost beyond it's target price.