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.