“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. Have a PortMon war story? Drop it in the comments below!

PortMon (Port Monitor) is a classic, lightweight utility from Microsoft’s Sysinternals suite (written by Mark Russinovich). Although it is legacy software (last updated for Windows XP/7), it remains an indispensable tool for debugging serial (RS-232) and parallel port communication on older systems or within virtual machines.

If you have ever found yourself scratching your head wondering, "Is my software sending the wrong data, or is the peripheral just ignoring me?" — you need PortMon .