def write_single_coil(addr, val)
      if val == 0
        query("\x5" + addr.to_word + 0.to_word)
      else
        query("\x5" + addr.to_word + 0xff00.to_word)
      end
      self
    end
def write_single_coil(addr, val)
      if val == 0
        query("\x5" + addr.to_word + 0.to_word)
      else
        query("\x5" + addr.to_word + 0xff00.to_word)
      end
      self
    end
Write a single coil

 @example
  write_single_coil(1, 0) => self

 @param [Integer] addr address coil
 @param [Integer] val value coil (0 or other)
 @return self