Cfrgtkky

I am new to LaTeX and I am trying to put multiple underbrace under a package using bytefield package. I want to have 4 underbrace consecutive to each other, but I am only able to put 2 and the other 2 appear with a space in between.

First I define the bitbox of the packet, then I put the underbrace below them.
I have review the bytefield documentation and there is no underbrace example. I found this question Bytefield: Word Group below blocks but it only puts one underbrace. With that answer I was able to put 2 together and 2 together but not consecutive to each other. The code I have is the following:

documentclass[border=10pt,png]{standalone}

usepackage{amsmath}

usepackage[endianness=big]{bytefield}

bytefieldsetup{boxformatting={centeringfootnotesize}}

begin{document}



    begin{bytefield}[bitwidth=1.1em]{21}       

         bitbox{1}{1} & bitbox{1}{2} & bitbox{1}{3} & bitbox{1}{4} & bitbox{1}{5} & 

         bitbox{1}{6} & bitbox{1}{7} & bitbox{1}{8} & bitbox{1}{9} & bitbox{1}{10} &

         bitbox{1}{11} & bitbox{1}{12} & bitbox{1}{13} & bitbox{1}{14} & bitbox{1}{15} &       

         bitbox{1}{16} & bitbox{1}{17} & bitbox{1}{18} & bitbox{1}{19} & bitbox{1}{20} & 

         bitbox{1}{...}\



         bitbox{0}{$underbrace{hspace{6.7em}}_{text{normalsize $A_0$}}$} &

         bitbox{15}{$underbrace{hspace{6.7em}}_{text{normalsize $A_1$}}$} &

         bitbox{0}{$underbrace{hspace{6.7em}}_{text{normalsize $A_2$}}$}     &   

         bitbox{15}{$underbrace{hspace{6.7em}}_{text{normalsize $A_3$}}$} \

    end{bytefield}

 end{document}

The result I obtain is:

And what I wish to obtain is this:

I am not sure why this space appears between the first 2 underbrace and the third one. I have change the hspace, the value inside the bitbox{}, put the bitbox inside the underbrace, but nothing seems to do the trick.

Thanks in advance for all your help.

Don't alternate between 0 and 15:

documentclass{article}

usepackage{amsmath}

usepackage[endianness=big]{bytefield}



bytefieldsetup{boxformatting={centeringfootnotesize}}



begin{document}



begin{bytefield}[bitwidth=1.1em]{21}

bitbox{1}{1} & bitbox{1}{2} & bitbox{1}{3} & bitbox{1}{4} & bitbox{1}{5} &

bitbox{1}{6} & bitbox{1}{7} & bitbox{1}{8} & bitbox{1}{9} & bitbox{1}{10} &

bitbox{1}{11} & bitbox{1}{12} & bitbox{1}{13} & bitbox{1}{14} & bitbox{1}{15} &

bitbox{1}{16} & bitbox{1}{17} & bitbox{1}{18} & bitbox{1}{19} & bitbox{1}{20} &

bitbox{1}{...vphantom{1}}\



bitbox{5}{$underbrace{hspace{6.2em}}_{text{normalsize $A_0$}}$} &

bitbox{5}{$underbrace{hspace{6.2em}}_{text{normalsize $A_1$}}$} &

bitbox{5}{$underbrace{hspace{6.2em}}_{text{normalsize $A_2$}}$} &

bitbox{5}{$underbrace{hspace{6.2em}}_{text{normalsize $A_3$}}$} \

end{bytefield}



end{document}

The 6.2 em has been computed by trial and error. Note the phantom in the last cell in order to set the dots at the right height.