Your code can be shortened a bit:

use strict;
use warnings;
use Tk;

my $columns_per_row = 12;

sub ASCII_Buttons {
    my $root = MainWindow->new();
    $root->title('MMG Server Options');

    my ($row,$col) = (1,1);
    for my $character (0..255) {
        my $label = sprintf("[%03d][%s]", $character, chr($character))
+;
        $root->Button(
                -text=>$label,
                -font => '-*-Lucida Console-Bold-R-Normal-*-*-160-*-*-
+*-*-*-*',
            )->grid(-row=>$row,-column=>$col,-sticky=>'nswe');
        if ($col>=$columns_per_row) {$row++;$col=0}
        $col++;
    }
}

ASCII_Buttons();
MainLoop;
[download]

Regards, mawe