\begin{tikzpicture}
    \begin{axis}[
            height = 4cm,
            width=\textwidth,
            xlabel={step(t)},
            %            ylabel={1= Up/ 0= Down},
            xmin=0, xmax=4,
            ymin=0, ymax=1,
            xtick={0,1,2,3,4},
            ytick={0,1},
            grid=both,
            grid style={line width=.8pt},
        ]
    \end{axis}
\end{tikzpicture}\\