I make LED cubes using PIC-18F4321 chips as MCU controllers. The serial port is set to 115K baud and tied to a USB PCB with a MC2200 chip. The MC2200 chip is recognized by windows and windows sets it to COM4 (or COM8 depending which different USB PCB used). I use Win7-Pro. I have "challenges" each time I want to start TT in it's recover mode to receive messages from that USB PCB. I mostly close TT and start over (several times, including plugging and unplugging the USB cable) to get a connection that finally works. Most of the time the setup/serial-port menu does not give enough selections in the COM portion. I do save the setups for every application ( a long list) and re-use the saved one for each.
Other LED cubes have RS232 serial ports (yes, it's old tech) and they work fine.
Help, and Respectfully,