my $b = "123\xC4" ;
  my $u = "a\xC4\x{107}\x{1C4}" ;

  show(unpack('C*',   $b)) ;  # 0x31, 0x32, 0x33, 0xC4
  show(unpack('C*',   $u)) ;  # 0x61, 0xC4, 0x107, 0x1C4

  { use bytes ;
    show(unpack('C*', $b)) ;  # 0x31, 0x32, 0x33, 0xC4
    show(unpack('C*', $u)) ;  # 0x61, 0xC3, 0x84, 0xC4, 0x87, 0xC7, 0x84
  } ;

  sub show {
    print join(", ", map(sprintf("0x%02X", $_), @_)), "\n" ;
  } ;