Sstrhsrtj

I would like to modify the code of this answer

documentclass[tikz, border=5pt]{standalone}

begin{document}

  tikzset{

    charge node/.style={inner sep=0pt},

    pics/sum block/.style n args={4}{

      code={

        path node (n) [draw, circle, inner sep=0pt, minimum size=9mm] {}

          (n.north) +(0,-1.5mm) node [charge node] {$#1$}

          (n.south) +(0,1.5mm) node [charge node] {$#2$}

          (n.west) +(1.5mm,0) node [charge node] {$#3$}

          (n.east) +(-1.5mm,0) node [charge node] {$#4$}

          ;

      }

    }

  }

  begin{tikzpicture}

    path pic at (10mm,0) {sum block={+}{-}{+}{-}}

    pic at (20mm,0) {sum block={}{+}{-}{}}

    ;

  end{tikzpicture}

end{document}

to get the output of this answer of a summation circle with four input ports separated by two perpendicular diameters.

Additionally, if the circle is drawn by

documentclass{article}

usepackage{tikz,mathtools,amssymb}

usetikzlibrary{shapes,arrows,positioning,calc}



begin{document}

    tikzset{

        port/.style     = {inner sep=0pt, font=tiny},

        sum/.style n args = {4}{draw, circle, node distance = 2cm, minimum size=5mm, alias=sum,%https://tex.stackexchange.com/a/234545/2288

            append after command={

                node at (sum.north) [port, below=1pt] {$#1$}

                node at (sum.west) [port, right=1pt] {$#2$}

                node at (sum.south) [port, above=1pt] {$#3$}

                node at (sum.east) [port, left=1pt] {$#4$}}},

        }

    begin{tikzpicture}[auto, node distance=5mm,>=latex',align=center,]

    node [sum={}{+}{-}{}] (sum) {};

    end{tikzpicture}   

end{document}

how can the two prependicular diameters be drawn?

Do you mean like this?

documentclass[tikz, border=5pt]{standalone}

begin{document}

  tikzset{

    charge node/.style={inner sep=0pt},

    pics/sum block/.style n args={4}{

      code={

        path node (n) [draw, circle, inner sep=0pt, minimum size=9mm] {}

          (n.north) +(0,-1.5mm) node [charge node] {$#1$}

          (n.south) +(0,1.5mm) node [charge node] {$#2$}

          (n.west) +(1.5mm,0) node [charge node] {$#3$}

          (n.east) +(-1.5mm,0) node [charge node] {$#4$}

          ;

        draw

          (n.north west) -- (n.south east)

          (n.south west) -- (n.north east)

          ;

      }

    }

  }

  begin{tikzpicture}

    path pic at (10mm,0) {sum block={+}{-}{+}{-}}

    pic at (20mm,0) {sum block={}{+}{-}{}}

    ;

  end{tikzpicture}

end{document}

It is possible to also append the lines in your second variant. And thanks to @marmot, it is possible to do so without paying further attention:

documentclass{standalone}

usepackage{tikz}



tikzset

  {

    port/.style     = {inner sep=0pt, font=tiny},

    cross/.style =

      {%

        path picture=%

          {

            draw

              (path picture bounding box.north west) --

                (path picture bounding box.south east)

              (path picture bounding box.south west) --

                (path picture bounding box.north east)

              ;

          }

      },

    sum/.style n args = {4}%

      {%

        draw, circle, node distance = 2cm, minimum size=5mm, cross, alias=sum,%https://tex.stackexchange.com/a/234545/2288

        append after command=%

          {%

            node at (sum.north) [port, below=1pt] {$#1$}

            node at (sum.west) [port, right=1pt] {$#2$}

            node at (sum.south) [port, above=1pt] {$#3$}

            node at (sum.east) [port, left=1pt] {$#4$}

          },

      },

  }

begin{document}

begin{tikzpicture}

  node [sum={}{+}{-}{}] (b) {};

end{tikzpicture}   

end{document}