docs: def Move(self, units):
          ' Move some distance units from current position '
          steps = units * self.SPU  # translate units to steps 
          if steps > 0:                                          # look for direction
              spi.SPI_write_byte(self.CS, 0x40 | (~self.Dir & 1))       
          else:
              spi.SPI_write_byte(self.CS, 0x40 | (self.Dir & 1)) 
          steps = int(abs(steps))     
          spi.SPI_write_byte(self.CS, (steps >> 16) & 0xFF)
          spi.SPI_write_byte(self.CS, (steps >> 8) & 0xFF)
          spi.SPI_write_byte(self.CS, steps & 0xFF)