The situation happens when the spaces of "data memory" get to be full, as the output window shows Program Size: data=230.0 xdata=13 code=30790 Under these situations some "variables" I used originally would be affected accidently. For example : ////////////////// unsigned int idata out,i; for(i=0;i<=256;i++) { out=i } /////////////////// We could use the "Debug Session" to monitor variable "i" and it could easily find the variable "i" may abnormally increase like i= 0 -> 1 -> 2 -> 200 --> 201 It seems that variable "i" is written by another data. Do anybody face with such condition as me? Thank you for your valuable information.