hello mitchell.kary,
please also access Jetson AGX Xavier Series Product Design Guide, and check chapter-13 for the [Figure 13-7. Jetson AGX Xavier UART Connections] for reference,
you may also refer to this discussion thread as see-also, Xavier4.3, How can I debug with ttyTSH0 instead of ttyTCU0? - #26 by JerryChang
thanks