example.tex

% D flip-flops (DFFs) and shift register
% Author: Martin Scharrer
\documentclass[a4paper,landscape]{article}

\usepackage{pgf,tikz}
\usetikzlibrary{calc,arrows}
\usetikzlibrary{circuits.logic.dff}
\usepackage{amsmath}
\usepackage[left=1cm,right=1cm]{geometry}
\pagestyle{empty}

\makeatletter

\makeatother

\begin{document}

\begin{tikzpicture}[font=\sffamily,>=triangle 45]
  \def\N{7}  % Number of Flip-Flops minus one

  % Place FFs
  \foreach \m in {0,...,\N}
    \node [shape=dffsr] (DFF\m) at ($ 3*(\m,0) $) {Bit \#\m};

  % Connect FFs (Q1 with D1, etc.)
  \def\p{0}  % Used to save the previous number
  \foreach \m in {1,...,\N} { % Note that it starts with 1, not 0
    \draw [->] (DFF\p.Q) -- (DFF\m.D);
    \global\let\p\m
  }

  % Connect and label data in- and output port
  \draw [<-] (DFF0.D) -- +(-1,0) node [anchor=east] {input} ;
  \draw [->] (DFF\N.Q) -- +(1,0) node [anchor=west] {output};

  % 'Reset' port label
  \path (DFF0) +(-2cm,+2cm) coordinate (temp)
    node [anchor=east] {reset};
  % Connect resets
  \foreach \m in {0,...,\N}
    \draw [->] (temp) -| (DFF\m.R);

  % 'Set' port label
  \path (DFF0) +(-2cm,-2cm) coordinate (temp)
    node [anchor=east] {set};
  % Connect sets
  \foreach \m in {0,...,\N}
    \draw [->] (temp) -| (DFF\m.S);

  % Clock port label
  \path (DFF0) +(-2cm,-2.5cm) coordinate (temp)
    node [anchor=east] {clock};
  \foreach \m in {0,...,\N}
    \draw [->] (temp) -| ($ (DFF\m.CLK) + (-5mm,0) $) --(DFF\m.CLK);

  % Clock port label
  \path (DFF0) +(-2cm,-3cm) coordinate (temp)
    node [anchor=east] {clock enable};
  \foreach \m in {0,...,\N}
    \draw [->] (temp) -| ($ (DFF\m.CE) + (-7.5mm,0) $) --(DFF\m.CE);
\end{tikzpicture}

\vspace{4cm}

\begin{tikzpicture}[font=\sffamily,>=triangle 45]
  \def\N{7}  % Number of Flip-Flops minus one

  % Place FFs
  \foreach \m in {0,...,\N}
    \node [shape=dff] (DFF\m) at ($ 3*(\m,0) $) {Bit \#\m};

  % Connect FFs (Q1 with D1, etc.)
  \def\p{0}  % Used to save the previous number
  \foreach \m in {1,...,\N} { % Note that it starts with 1, not 0
    \draw [->] (DFF\p.Q) -- (DFF\m.D);
    \global\let\p\m
  }

  % Connect and label data in- and output port
  \draw [<-] (DFF0.D) -- +(-1,0) node [anchor=east] {input} ;
  \draw [->] (DFF\N.Q) -- +(1,0) node [anchor=west] {output};

  % Clock port label
  \path (DFF0) +(-2cm,-2.5cm) coordinate (temp)
    node [anchor=east] {clock};
  \foreach \m in {0,...,\N}
    \draw [->] (temp) -| ($ (DFF\m.CLK) + (-5mm,0) $) --(DFF\m.CLK);

  % Clock port label
  \path (DFF0) +(-2cm,-3cm) coordinate (temp)
    node [anchor=east] {clock enable};
%   \foreach \m in {0,...,\N}
%     \draw [->] (temp) -| ($ (DFF\m.CE) + (-7.5mm,0) $) --(DFF\m.CE);
\end{tikzpicture}

\end{document}