Quote:
Originally Posted by Dave Flowerday
Take a look in the device manager (Control Panel->System->Hardware->Device Manager, under "Ports") and make sure you see two instances of "Silicon Labs CP210x..." there. If you only see one, then unplug one of the field controllers and look at which COM port is listed for the controller which is still plugged in. After that, unplug that controller and plug in the other one and look at which COM port is shown. If they're the same, then that is the cause of the problem. Some of the field controllers at one point were shipped with identical serial numbers which means that Windows has no way of telling them apart when they're both plugged in.
It is definitely possible and has been done at many events.
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What was happening was that I would go into the properties, manually set a com port, disconnect and reconnect the device, and then see that the com port was changed. If I disconnected that device and put another in, it used that com port again. Both fields would try to use the same com port Once I put the 2nd device in, the 1st one in device manager got the beloved yellow (!) and no 2nd device showed up, and neither field would work. I couldn't even change the com port within the settings. Disconnecting either field would cause the other to work, back on the whatever port was established by the UART to USB driver that I set before.
Now, I can be totally off-base, but I went with VexLover's suggestion to us the USB hub and it worked like a charm.