Hello all, I have a bizarre problem that I hope someone will be kind to help me. I'm working with compiler ver7.02b, RTX51-full, and T89C51RD2. One of the variables (X) placed in xdata (address 0x19CC) is initialized to 3. For some bizarre reason when program is running this value is changed to zero. There isn't any place in my code where I set this variable to zero, because it's illegal in my case (acceptable values can be from 3 to 255). The compiler's optimization level is set to zero. I'm using Ceibo's emulator DS-51, but he doesn't support software breakpoints with write specific data to specific address location (I wanted to stop execution when zero is written to this specific address location). Does someone have any idea how to proceed? Thanks in advanced, Ruven