I can't see how 0x8404 is the 'reverse' of 0x1021 by any stretch of my imagination,(*)

but a simple brute force conversion yields:

#! perl -slw
use strict;

sub crc16 {
     use constant POLY => 0x8408;
     my $crc = 0;
     for my $c ( unpack 'C*', $_[0] ) {
         $crc ^= $c;
         for my $b ( 0 .. 7 ) {
             my $carry = $crc & 1;
             $crc >>= 1;
             if( $carry ) {
                 $crc ^= POLY;
             }
         }
     }
     return $crc;
}

my $data = "\x64\x01";

printf "crc: %04x\n", crc16( $data );

__END__
C:\test>997760.pl
crc: 13bc
[download]

Which works for the (inadequate, single) sample data.

(* 0x1021 -> 0001_0000_0010_0001 bitwise reversed -> 1000_0100_0000_1000 -> 0x8408 )