I can't say about Device::Serial as I haven't used it. The 'H' pattern will pack the bytes in Little-endian order. This may not be what your driver wants. The 'N' pattern will pack your bytes into Network order which is more universal. It would seem a well written driver would do this conversion for you so I'm a little suspicious of the API.

I googled and did a CPAN search and didn't come up with any module named Device::Serial; could you message me a link to the source? Write() would not be the correct call under native perl but the module author may have used it that way I really won't know till I read the source.

Debugging this kind of hardware/software things can be nigh on impossible without the right tools. You certainly need something to monitor the output of your serial port to verify that it is sending something and to check baud-rate and format. You at least need to loopback the TX to the RX and verify that you can read what you wrote.