So let me see if I have this straight. To use the 2Kbytes On chip XRAM (accessed as XDATA memory space) on a ADuC831, I need to 1) Copy START_AD.A51 into my project folder 2) Add this file to my project so that it will be used on startup as opposed to the STARTUP.A51 file. 3) Make sure that the START_AD.A51 has the XRAM enable bit set to 1. 4) Make sure that the extended stack pointer is not used. 5) write code and compile. At this point, I should be able to reference the 2Kbytes of XRAM by just assigning variables to the XDATA memory space. My project does not require any more than this 2K of XRAM space. So my question is.. Does the compiler know to place XDATA variables in ONLY the lower 2K of the XDATA space? Theoretically the chip can at least address 64K and up to 16MB of XDATA. In addition, how can I verify proper functionality in the debugger? Any help appreciated... MG