Perl: Split binary data into byte array

(just trying to document this; self answer to follow)

I basically wanted to convert a binary string to an array/list of bytes (so as to allow indexing, and avoid using substr, because its syntax complicates things for me), and I came up with the following MWE:

#!/usr/bin/env perl

use warnings;
use strict;

# use open ':raw';      # Unknown PerlIO layer class ':raw'
use open IO => ':raw';

binmode(STDIN);
binmode(STDOUT);

# create orig 8-bit byte array/list
my @atmp = (0x80, 0x23, 0x14, 0x0d, 0x0a, 0x00, 0x00, 0x80, 0x43, 0x00, 0x00);

# make a copy of portion
my @atmp2 = (0) x 2;
@atmp2[0..1] = @atmp[7..8];

# print output
print "Copied atmp2 contents as hex: " . join(", ", unpack("H2"x2, pack("C"x2,@atmp2))) . "\n";
print "Copied atmp2 as ushort (16bit) int: " . unpack("S", pack("C"x2, @atmp2));
# doublecheck value by routing through printf with format specifier:
printf(" [%d]\n", unpack("S", pack("C"x2, @atmp2)));


# now, the same data as string:
my $indata = "\x80\x23\x14\x0d\x0a\x00\x00\x80\x43\x00\x00";

# create byte array (by converting string $indata to array/list with `split`)
my @btmp = split('',$indata);
print "lastindex: " . $#btmp . "\n";

# make a copy of portion
my @btmp2 = (0) x 2;
@btmp2[0..1] = @btmp[7..8];

# print output
print "Copied btmp2 contents as hex: " . join(", ", unpack("H2"x2, pack("C"x2,@btmp2))) . "\n";
print "Copied btmp2 as ushort (16bit) int: " . unpack("S", pack("C"x2, @btmp2));
# doublecheck value by routing through printf with format specifier:
printf(" [%d]\n", unpack("S", pack("C"x2, @btmp2)));

Running this code results with:

$ perl test.pl 
Copied atmp2 contents as hex: 80, 43
Copied atmp2 as ushort (16bit) int: 17280 [17280]
lastindex: 10
Argument "M-\0" isn't numeric in pack at test.pl line 38.
Argument "C" isn't numeric in pack at test.pl line 38.
Copied btmp2 contents as hex: 00, 00
Copied btmp2 as ushort (16bit) int: 0 [0]

How do I get the second part (btmp2) to behave the same as the first part (atmp2)?