Mark Russinovich at www.sysinternals.com has released freeware utility PortMon which monitors and displays all serial and parallel port activity on NT and Win9x systems. Useful to Windows NT admin.

Portmon is a GUI/device driver combination that monitors and displays all serial and parallel port activity on a system. It has advanced filtering and search capabilities that make it a powerful tool for exploring the way NT works, seeing how applications use ports, or tracking down problems in system or application configurations.

Portmon understands all serial and parallel port I/O control (IOCTLs) commands and will display them along with interesting information regarding their associated parameters. For read and write requests Portmon displays the first several dozen bytes of the buffer, using '.' to represent non-printable characters. The Show Hex menu option lets you toggle between ASCII and raw hex output of buffer data.

New Riders has good NT texts.