\begin{tikzpicture}

\path
	(0, 0) node(flash)[draw, rectangle, 
	minimum height=1cm, minimum width=2cm] {Flash}

	(0, 1.5) node(esp8266)[draw, rectangle, 
	minimum height=1cm, minimum width=2cm] {ESP8266}

	(3.5, 1.5) node(cp201x)[draw, rectangle, 
	minimum height=0.75cm, minimum width=1cm]
	{CP201x}

	(5.5, 1.5) node(usb)[]
	{USB}
;

\draw[-] (esp8266) -- node[node font=\footnotesize, right]{QSPI} (flash);
\draw[-] (esp8266) -- node[node font=\footnotesize, above]{UART} (cp201x) -- (usb);

\node[rectangle, draw, fit=(esp8266) (flash), inner sep=2 mm,
	label={[name=esp12_label,anchor=south]ESP-12}]
	(esp12){};

\node[rectangle, draw, thick, fit=(esp12_label) (esp12) (cp201x), inner sep=3 mm,
	label={[anchor=north]south:NodeMCU}]
	(nodemcu){};

\end{tikzpicture}