First of all, with IAR (on a microcontroller of the RL78 family) I can do this by reserving a location for the unique id in the .xcl file, and using (in the source code) #pragma location to define a __no_init variable on the address where I put my ID.
The problem is that in HEW I can't find an alternative for __no_init, so I don't know how to define a variable in the location where i will put my unique id whithout initialize it and lose the data.
Do you guys have an alternative solution?
The definition __no_init is a compiler function. HEW is not a compiler. There are several different compilers that can be used with HEW. Without information it is impossible to give good advice. Usually you can reserve an area in the linker options. Access to this can be done using pointer from your application. You can also place a variable in an own section. By default data placed in user defined sections is not initialized. You can place this section at the address you like.