$ cat a.pl
use strict;
use warnings;
binmode(STDOUT, ':raw');
{ utf8::downgrade( my $x = chr(0xE9) ); print $x; }
{ utf8::upgrade(   my $x = chr(0xE9) ); print $x; }
{                  my $x = chr(0x100);  print $x; }

$ perl a.pl | od -t x1
Wide character in print at a.pl line 6.
0000000 e9 e9 c4 80
0000004