Open Serial commands through rs232

I have a hdmi multi view box that I want to command through the RS232 port in my Android automation box. I plan to get a usb to rs232 cable then hopefully automate sending hex codes to it through tasker.

I can't see where this can be done I only find the Bluetooth serial which I am not planning to use as first priority

I can find terminally programs for Android but I don't believe they have tasker plugins. I don't particularly want to use autoinput as that would require interruption of what's showing on the screen.