$bit_10 = \$bit[10];
$bit_9  = \$bit[9];
$bit_10_9 = $$bit_10 . $$bit_9;

$bit_10_9_mb = $r2Frame->Menubutton(
                            -textvariable => \$bit_10_9,
                            -menuitems => [['command' => "00",
                                            -command => sub {$bit[10] = 0; $bit[9] = 0;}],
                                           ['command' => "01",
                                            -command => sub {$bit[10] = 0; $bit[9] = 1;}],
                                           ['command' => "10",
                                            -command => sub {$bit[10] = 1; $bit[9] = 0;}],
                                           ['command' => "11",
                                            -command => sub {$bit[10] = 1; $bit[9] = 1;}]],
                            -background => "black",
                            -foreground => "white",
                            -tearoff => 0,
                            -relief => "groove",
                            )->pack(-side => "left", "-after" => $bit_11_entry);