sprintf x signed values

Hi people
I´m working with 52235 and I´m trying to print a negative value for a char (int8) wich is -2, by using sprintf function, but the output is "254".  
I did:
{
...
int8 sdata_8;

   sdata_8=-2;
   sprintf(lcd_controller.text_data_array,"%hi.", sdata_8);
...

}
I did the same experience using int16 and so I had success..
Is there some special care to use sprintf with char?

By the way, how can copy a negative value of a int8 to a int16?
I tryied:
sdata_16=sdata_8; and I got the calue 254 for sdata_16  ..and not -02 ...

Thanks guys ...
Ricardo Raupp