Why M218 can not keep the retain data after power off?
If you define a variable like "aaa", and you move it to %MW0. %MW0 is in retain area, but variable "aaa" is not a retain data, so "aaa" will over-write the %MW0 value, which cause %MW0 can not retain data. If you want variable "aaa" to keep data, you just define the variable as retain variable.