my $data_ref = pack ('C*', (0x81 , 0x55, 0x00, 0xE0)); 

##</code><code>##

 $ say "0x81, 0x55, 0x00, 0xE0"
129
85
0
224
 $ say "unpack 'U0C*', pack 'C*', 0x81, 0x55, 0x00, 0xE0"
194
129
85
0
195
160