A PL2303 serial-over-USB device is configured to receive-only data. There is an explanation of tty vs. cu here:
MacOS: what's the difference between /dev/tty.* and /dev/cu.*?
That being said, when configuring data collection software, one has to choose either /dev/tty.usbserial or /dev/cu.usbserial. I would like to understand the facts and the decision-making thought for selecting tty or cu.