   @doc """
   Set or clear the Request To Send signal.
   """
+  @spec set_rts(pid, boolean) :: :ok | {:error, term}
   def set_rts(pid, value) when is_boolean(value) do
     GenServer.call pid, {:set_rts, value}
   end

  This is a convenience function for calling `set_break/2` to enable
  the break signal, wait, and then turn it off.
  """
  def send_break(pid, duration \\ 250) do
    set_break(pid, true)
    :timer.sleep(duration)
    set_break(pid, false)
  end

    * `:ebadf` - the UART is closed
    * `:einval` - the UART is in active mode
  """
  @spec read(pid, integer) :: binary | {:error, term}
  def read(pid, timeout \\ 5000) do
    GenServer.call pid, {:read, timeout}, genserver_timeout(timeout)
  end
