Why aren't multiple bluetooth SPP devices with different COM port assignments unique?

Question

Here's the setup: I have two bluetooth devices paired with a single PC. Both are SPP, intended to be used with separate virtual COM ports. One device is assigned COM9, the other is assigned COM11. If I open the COM9 port, it 'sees' the data from the COM11-paired device, even though I didn't open the COM11 port.

It looks as if any data from a paired device, regardless of which COM port it is paired with, will be received on whatever COM port has been opened. I would have expected that data from the device paired with COM9 would only be received if I opened the COM9 virtual port, etc.

Can anyone tell me why the paired ports aren't behaving uniquely? Any way to force them to be unique?

Answer 1

typically I have seen 2 com ports (incoming and outgoing) that gets assigned to a single device, are you sure com 9 and 11 in your care are not the incoming and outgoing port to the same device ?

Answer 2

I have observed a similar behaviour on Windows 7 and Windows 8. I have paired two SPP Bluetooth devices. Thus Windows has created four virtual COM ports: one incoming and one outgoing for each device. I then opened the two incoming ports. Nevertheless, I could not connect both devices simultaneously. The first one gets connected to whatever incoming port and the second one cannot connect as long as the first is connected. It looks as if Windows can accept only one incoming connection, on whatever incoming virtual COM port.