makemessage{FooMsg,3,16,"Foo Message Definition"}
addelement{FooMsg,0,0,3,"Spare"}
addelement{FooMsg,0,3,13,"Message Unique ID"}
addelement{FooMsg,1,0,8,"Error ID"}
addelement{FooMsg,1,8,8,"Module ID"}
addelement{FooMsg,2,0,16,"Reserved"}

documentclass{article}

usepackage{bytefield}

begin{document}

    begin{bytefield}[bitwidth=1.1em, endianness=big]{16}
         bitheader{0-15} \
         begin{rightwordgroup}{Word 0}
         bitbox{13}{Message Unique ID} & bitbox{3}{Spare}
         end{rightwordgroup}\
         begin{rightwordgroup}{Word 1}
         bitbox{8}{Module ID} & bitbox{8}{Error ID}
         end{rightwordgroup}\
         begin{rightwordgroup}{Word 2}
         bitbox{16}{Reserved}
         end{rightwordgroup}\
    end{bytefield}

end{document}