led matrix display
If you always want your message to scroll, just code it that way.
If you want to be able to select how it displays (horizontal or vertical scroll, direction, speed, Oscillate, fade in, wipe,etc etc) then code those control functions into your display micro controller and send 'escape' sequences from the PC to set the control values without being displayed, then you send the string to be displayed.
Do as much on the micro controller a you can.