\begin{tikzpicture}
	\node[name=s,shape=circle split,draw=gray!40,line width=0mm,minimum size=1cm] {};
	\begin{scope}[on background layer]
		\fill[black!50] (s.base) ([xshift=-0mm]s.east) arc (0:180:0.5cm-0mm)--cycle;
		\fill[white!50] (s.base) ([xshift=0mm]s.west) arc (180:360:0.5cm-0mm)--cycle;
	\end{scope}
	\node (input1) at (0.0, -1.25) {$x_1$};
	%\node (input2) at (0.75, -1.25) {$x_2$};

	\node (output) at (0, 1.25) {$y \in \{0,1\}$};

	%\node at (0,0.25) {$f$};
	\onslide<11->{\node at (0,-0.25) {$0$};}

	\draw [o=1pt] (input1) -- (s.270);
	%\draw [o=1pt] (input2) -- (s.285);
	\draw [->] (s.90) -- (output);

\end{tikzpicture}