Hi Stefano,
yes, you can watch the variables in real time. If you have a problem, you can have problem with safety.
Please, go to the freemaster_cfg.h in your project and look at the value of safety.
#define FMSTR_USE_TSA_SAFETY 0 /* enable access to TSA variables only */
If you have 0, you can read variables, if you have 1, you cannot.
For more information about TSA Safety, please go to the documentation on C:\Freescale\FreeMASTER_Serial_Communication_Driver_V1.8.1\doc FMSTRSCIDRVUG.pdf.