How can I communicate the computer with the led screen

How can I communicate the computer with the led screen. How can I communicate with the computer the led screen with the rs 485 protocol. There is software written in c on the led screen. I want to make the computer communicate with the led screen using java se.
led screenshot
I can do projects in Android and Web environment using Java language. But I cannot understand how a software will communicate with a hardware.
With regards to serial communication

Both ends need to have the same physical hardware bus layer. RS-485 is one such physical hardware bus layer that allows for point-to-point communications with suitable protocol and applications implemnentation.

Both ends need firmware software to regulate the communications on the hardware bus. This is typically a protocol, a set of rules that defines who talks when (who is silent when), how communications is initiated, maintained, and terminate, the format of message, whether messaging is acknowledged or not, error handling.

Other firmware/software is needed to handle the data, put it where it needs to go, and do whatever interpretation of the data is required.

Sometimes the firmware/software is proprietary for a given application.
Sometimes the firmware/software is commercially available, licensed at various levels.

Not all devices have an implementation of communications functionality or are so locked down with a proprietary protocol and application that they're inaccessible without licensed access.

I saw a list of industrial protocols about 12 years ago that listed over 500 known industrial protocols and there were a dozen that I had run into that were not on the list.