“Serial debugging without a monitor is like lip-reading through a brick wall.” Fire up PortMon, watch the bytes flow, and fix that ancient hardware.
If you are on and just need to see "what data is going in and out," skip Portmon and use a modern alternative like HW Virtual Serial Port or a paid tool like Serial Port Monitor by Eltima, as Portmon's kernel driver often fails to load on modern architecture. how to use portmon