>>I have many simulators and some utilities that send and receive data via a serial port. this works fine in windows xp but on windows 7 the utilities never receive any data through the serial port. If I switch to the modem serial port and pass ATZ, it returns with an OK immediately so I know it is working. If I put any of the simulators (that basically continuously send data through the port) on com1 and then put another utility/simulator that reads data on another com port (or on another machine on a comm port connected via a cable) , the one receiving never fires the oncomm event of the mscomm control.
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>>Any ideas what would prevent data from coming in a serial port?
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>SWAG - firewall, either at the port or application level?
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>Is the COM port a real one, or one implemented via USB?

That was one my first suspicions, but I've never heard of a firewall that works on the serial ports? The workstation only has windows 7 built in firewall (the hardware firewalls work on the internet tcpip ports). Normally I'm prompted to allow or block or I have to set up the port manually or exe manualy (like with sqlserver for remote connections). I've never had to do that with serial ports though. I'll set an exception for it just in case and do some more testing.....there is no way to set the serial port (that I can see) so it could only be at the application level....

I've tried using one hard comm port (com1) and a usb-->serial cable (with driver installed) between then running one app to send on one port and the other to receive on the other port. This works on windows xp. I've also tried using the one single hard comm port with a serial cable to another workstation's serial port and again, running send on one and receive on the other machine works fine.

As soon as I try on the the windows 7 machines though, neither scenario receives data. Although I considered a firewall (even though I never heard of one monitoring serial ports), I doubted it since the same test on windows 7 to a modem works fine. It sends and receives to the modem. why would the modem data go through then?