I read in the manual that the stack cannot be located off-chip in XDATA. Can someone please confirm this? I was wondering what would happen if I modify the STARTUP.A51 to place the stack pointer in XDATA (don't want to try yet!). I was using Sandeep Dutta's freeware C compiler which did allow the stack in xdata, and was wondering why Keil does not allow it. I have a large program in a FLASH chip, and very little precious iDATA space left despite my best efforts, and now the program is going off in the weeds whenever I add routines, and I am 90% sure it is a stack space problem. Speed is not an issue. Thanks!