\documentclass{standalone}

\usepackage{tikz}
\usepackage{tikz-timing}
\usepackage{newpxtext}
\usepackage{newpxmath}

\begin{document}
\begin{tikztimingtable}[timing/d/background/.style={fill=white}]
  \small clk & 2L 2{7C} \\
  \small u\_en & 2D{u\_en} 14D{$\overline{\texttt{u\_en}}$}\\
  \small addr & 2U 14D{3} \\
  \small wr\_en & 2U 14H \\
  \small d\_in & 2U 14D{0xDEADBEEF} \\
  \small en & 9D{u\_en} 7D{$\overline{\texttt{u\_en}}$}\\
  \small stack[addr] & 9U 7D{0xDEADBEEF} \\
  \extracode
  \node[help lines] at (2,2.25) {\tiny 1};
  \node[help lines] at (9,2.25) {\tiny 2};
  \begin{pgfonlayer}{background}
    \vertlines[help lines]{2,9}
  \end{pgfonlayer}
\end{tikztimingtable}
\end{document}