\chapter{Instruction Set Architecture}
\section{Encoding}
\def\minY{0} \def\maxY{0.5}
\def\minX{-7} \def\maxX{7}

\begin{tikzpicture}
	\draw (\minX, \minY) -- (\maxX, \minY);
	\draw (\minX, \minY) -- (\minX, \maxY) node[above] {31}; %{$y$}; Note the $'s, those make something math stylized.
	\draw (\maxX, \minY) -- (\maxX, \maxY) node[above]{0};
\end{tikzpicture}