code: def UXTB(self, params):
          
          Ra, Rb = self.get_two_parameters(r'\s*([^\s,]*),\s*([^\s,]*)(,\s*[^\s,]*)*\s*', params)
  
          self.check_arguments(low_registers=(Ra, Rb))
  
          def UXTB_func():
              self.register[Ra] = (self.register[Rb] & 0xFF)
  
          return UXTB_func
docs: UTXB Ra, Rb
  
          Zero extend the byte in Rb and store the result in Ra