If it's about storing some values here and there, it's better to store them in FLASH than in ERAM(XRAM) which would require permanent (battery) power. David said this above, twice.

The 'V51Rx2 can reprogram its own FLASH through a process called by NXP IAP. This can be utilized for storing constants etc. with certain care (e.g. taking into account the endurance, the fact that the program has essentially to "stop" during writing, that there's no bytewise rewritability and a whole 128-byte sector must be erased before writing, etc.) I believe the 'LV' is no different in this respect, although I've never tried personally.

I was about to find some example code to you, and entered "p89v51rd2 iap" into google, to find out that it leads to my own webpages... I guess this is like getting old, I don't remember what I've written a couple of years ago... :-(

JW