unsigned char Var1;
signed char Var2;

void MyFunction(unsigned char* Var);

MyFunction(&Var2); // This creates an error

template <typename T>
void MyFunction(T* Var);

template <typename T>
void MyFunction(T* Var)
{
   static_assert(sizeof(T) == 1, "Wrong type. Can only deal with 8-bit types.");
   ...
}