Simeon Cran wrote in a message to all:

SC> But it got me wondering how it's done. At first I thought it
SC> was a simple matter of opening the com port as READONLY and
SC> DENYNONE, and this works reasonably well. Then you can use
SC> DosDevIoctl calls to get info from the serial port device
SC> driver.
* * *
SC> Anyone got any ideas about how PMLM does it?

SIO creates alias devices in addition to the standard ones.  For example,
COM1 is aliased by $SIO$1, COM2 is aliased by $SIO$2, etc.  Since locking
and exclusion are handled by the file system router, there is no contention
if the device names are different.

-- Mike


---