Hi Sanjeev,

P3.3 is used to switch from one half of the ROM to the other, and the upper half can be code space because on power up P3.3 is automatically set (default port state).

The code will control when P3.3 is cleared, but once it's cleared, you'd be executing data (assuming as you said that data is in the lower half).

More likely, you've got 128K of code space (perhaps including const data) with duplicates for interrupt vectors in each half, and code for switching between the two halves. Search for code banking.

Dennis