Alignment of nodes and scopes in tikz matrix?

Question

I am trying to fix the positions of the arrows of the following diagram without much success. I would like the arrows to be centered (both horizontally and vertically) in the matrix cell no matter which way they are pointing.

The arrows are defined by macros of LARROW RARROW and DARROW.

MWE:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shapes.multipart,shapes.gates.logic.IEC,shapes.arrows,positioning,decorations.markings}


\begin{document}

\begin{tikzpicture}[use IEC style logic gates, LFSR/.style={
rectangle split, rectangle split horizontal=true, rectangle split parts=#1, draw, anchor=center}, ARROW/.style={draw,thick,single arrow,single arrow head extend=3pt,transform shape}]
\def\Byte(#1,#2,#3,#4){%
\node[LFSR=3,name=#1] {\nodepart{one}#2\nodepart{two}#3\nodepart{three}#4};
}
\def\LFSR(#1,#2,#3,#4){%
\begin{scope}[decoration={
    markings,
    mark=at position 0.6 with {\arrow{latex}}}]
    \Byte(LFSR0,#1,#2,#3)
    \node[xor gate, draw, logic gate inputs=nn, logic gate input sep=0.3cm, rotate = 180, below = 1.4cm of LFSR0.one, xshift=2mm, xor gate symbol ={\scalebox{-1}{\small=1}}, logic gate symbol align = {bottom}] (Xor) {\parbox[t][0.75cm]{0.7cm}{\scalebox{-1}{\small XOR}}};
    \draw (LFSR0.two south) |- (Xor.input 2);
    \draw (LFSR0.three south) |- (Xor.input 1);
    \draw (Xor.output) -- ++(left:3mm) node[anchor=north,inner sep=0pt] (hook1) {};
    \draw[postaction={decorate}] (hook1) |- node [near start, left] {#4} (hook1|-LFSR0.west);
    \draw (hook1|-LFSR0.west) -- (LFSR0.west) {};
    \draw[-latex] (LFSR0.one north) ++(up:1mm) node[anchor=center,inner sep=0pt] (hook2) {} -- (LFSR0.three south |-hook2);
\end{scope}
}
\def\RARROW{\node[rectangle,draw] {
    \parbox[b][1cm]{0pt}{\begin{tikzpicture}
        \node[ARROW] {};
    \end{tikzpicture}}
    };
}
\def\LARROW{\node[rectangle,draw,rotate=180] {
    \parbox[t][1cm]{0pt}{\begin{tikzpicture}
        \node[ARROW] {};
    \end{tikzpicture}}
    };
}
\def\DARROW{\node[rectangle,draw,align=center] {
    \begin{tikzpicture}
        \node[ARROW,rotate=-90] {};
    \end{tikzpicture}
    };
}
\matrix[row sep=0, column sep=2.5mm]{
    \LFSR(1,1,1,0) &\RARROW& \LFSR(0,1,1,0) & \RARROW & \LFSR(0,0,1,1) & \RARROW & \LFSR(1,0,0,0)\\
    \node[anchor=east,minimum height=9mm]{$t=0$};   & &
    \node[anchor=east,minimum height=9mm]{$t=1$};   & &
    \node[anchor=east,minimum height=9mm]{$t=2$};   & &
    \node[anchor=east,minimum height=9mm]{$t=3$};   \\
    & & & & & & \DARROW\\
    \LFSR(1,1,1,0) &\LARROW& \LFSR(1,1,0,1) &\LARROW& \LFSR(1,0,1,1) &\LARROW& \LFSR(0,1,0,1)\\
    \node[anchor=east,minimum height=9mm]{$t=7$};   & &
    \node[anchor=east,minimum height=9mm]{$t=6$};   & &
    \node[anchor=east,minimum height=9mm]{$t=5$};   & &
    \node[anchor=east,minimum height=9mm]{$t=4$};   \\
};
\end{tikzpicture}

\end{document}

Answer 1

Below I put my solution to your problem (err... a little bit modified =)

I rewrote the code, hope it has not been too difficult to understand.

\documentclass [tikz] {standalone}

\usetikzlibrary{calc}
\usetikzlibrary{matrix}
\usetikzlibrary{fit}
\usetikzlibrary{shapes.arrows}
\usetikzlibrary{shapes.gates.logic.IEC}

\tikzset{
    bit/.style = {draw, thick, minimum size = 1 cm, anchor = west}
    , port/.style = {draw, thick, minimum size = 2 cm}
    , space/.style = {minimum size = 1 cm}
    , flow/.style = {->, thick}
    , label/.style = {anchor = east}
    , inside/.style = {minimum size = 1 cm}
    , next/.style = {single arrow, draw, minimum size = 8mm}
}


\newcounter{cellcounter}

\newcommand{\myarrow}[1]{
    \begin{tikzpicture}
        \node [next, rotate = #1]{};
    \end{tikzpicture}
}   

\pgfmathsetmacro{\inputonedistance}{1 / 3}
\pgfmathsetmacro{\inputtwodistance}{2 / 3}

\newcommand{\mycell}[5]{
    \begin{tikzpicture} [use IEC style logic gates]
        \node [port]  (port) {};
        \node [inside, anchor = north]  (port symbol) at (port.north){\texttt{=1}};
        \node [inside, anchor = south]  (port name) at (port.south){\LARGE \texttt{#2}};

        \coordinate (port right 1) at ($(port.north east)!\inputonedistance!(port.south east)$);
        \coordinate (port right 2) at ($(port.north east)!\inputtwodistance!(port.south east)$);

        \node [space, anchor = south east] (space 0) at (port.north east) {};

        \node [bit, anchor = south] (bit 0) at (space 0.north east) {\texttt{#3}};
        \node [bit] (bit 1) at (bit 0.east) {\texttt{#4}};
        \node [bit] (bit 2) at (bit 1.east) {\texttt{#5}};

        \node [space, anchor = south] (space 1) at (bit 0.north) {};
        \node [space, anchor = south] (space 2) at (bit 2.north) {};

        \draw [flow] (bit 1) |- (port right 1);
        \draw [flow] (bit 2) |- (port right 2);
        \draw [flow] (space 1.center) |- (space 2.center);

        \node [space, anchor = south west] (space 3) at (port.north west) {};
        \node [space, anchor = south east] (space 4) at (space 3.north west) {};
        \node [space, anchor = east] (space 5) at (port.west) {};

        \node [label] (label 1) at ($(space 4)!0.5!(space 5)$) {\texttt{#1}};

        \draw [flow] (port) -| (label 1.east) |- (bit 0);
        \draw [flow] (port) -| (label 1.east) |- (bit 0);

        \node [fit = (port) (bit 2) (label 1) (space 2)] (base) {};
        \node [anchor = north] at (base.south) {\(t = \thecellcounter\) \stepcounter {cellcounter}};
    \end{tikzpicture}
}

\begin{document}
    \begin{tikzpicture} 
        \matrix (m) [matrix of nodes, nodes in empty cells, nodes = {minimum size = 2cm}]{
            & & & & & & & & & & & & & & \\
            & & & & & & & & & & & & & & \\
            & & & & & & & & & & & & & & \\
            & & & & & & & & & & & & & & \\
            & & & & & & & & & & & & & & \\
            & & & & & & & & & & & & & & \\
            & & & & & & & & & & & & & & \\
        };

        \node at (m-4-2) {\mycell{0}{XOR}{1}{1}{1}};

        \node at (m-2-6) {\mycell{0}{XOR}{0}{1}{1}};
        \node at (m-2-10) {\mycell{1}{XOR}{0}{0}{1}};
        \node at (m-2-14) {\mycell{0}{XOR}{1}{0}{0}};

        \node at (m-6-14) {\mycell{1}{XOR}{0}{1}{0}};
        \node at (m-6-10) {\mycell{1}{XOR}{1}{0}{1}};
        \node at (m-6-6) {\mycell{1}{XOR}{1}{1}{0}};

        \node at (m-3-4)  {\myarrow{45} };
        \node at (m-2-8)  {\myarrow{0}  };
        \node at (m-2-12) {\myarrow{0}  };
        \node at (m-4-14) {\myarrow{270}};
        \node at (m-6-8)  {\myarrow{180}};
        \node at (m-6-12) {\myarrow{180}};
        \node at (m-5-4)  {\myarrow{135}};

    \end{tikzpicture}
\end{document}