Steven van Loef wrote in a message to All:

 SvL> Does someone know how to monitor a com port while another
 SvL> app is using that comport. I know it is possible, because

Steven, you'll have to open the port yourself.

rc = DosOpen("COM2", &hFile, &ulAction, 0L, FILE_NORMAL,
             FILE_OPEN, OPEN_ACCESS_READWRITE | OPEN_SHARE_DENYNONE,
             0L);

I have successfully (unintentionally) screwed-up quite a few local mail
transfers by "monitoring" the port this way.  If you want to keep
this from happening, you'll have to use OPEN_ACCESS_READONLY instead of
OPEN_ACCESS_READWRITE.

Hope this helps.

GeeCee/2
Team OS/2 New England 
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