So, you are sending magic numbers to a mystery device which may or may not be responding to one or more of those magic numbers. You are expecting some sort of output from that mystery device but you are not getting that output and you can't figure out why.
You are the one who knows what the mystery device is, what information you are supposed to send it, and how it is supposed to respond but you can't determine why it isn't working the way you think it should. We know nothing about your mystery device except that it is some sort of serial LED display. How do you expect us to help?
Don