\font\test=mtex at 24pt
\baselineskip 50pt
\def\c#1{\setbox0=\hbox{\test\char#1}%
 \ifdim\wd0>0pt\box0\lower3pt\hbox{\fiverm\the#1}\ \fi}

\noindent
{\loop
 \c{\count0}\ifnum\count0<255\advance\count0 by1 \repeat
}