Configure the PORTEMUPortParamsstructure to specify attributes for the virtual COM port. This structure stores Bluetooth specific information, such as the channel and Bluetooth address information.

• For a server port, set flocaland channel, as the following example shows.
  
  

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  PORTEMUPortParams pp; memset (&pp, 0, sizeof(pp)); pp.flocal = TRUE; pp.channel = channel & 0xff;

  The preceding example configures a server port by setting flocalto TRUE. This enables a server COM port to accept incoming connections at the specified channel.
  
  

  Note:
  To avoid conflicts, when you are selecting the server channel, it is recommended that you set channelto RFCOMM_CHANNEL_MULTIPLE (0xfe). This configures RFCOMM to use the next available channel.

• For a client port, set the device, channel, and the uiportflagsmembers of PORTEMUPortParamsas the following example shows.
  
  

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  PORTEMUPortParams pp; memset (&pp, 0, sizeof(pp)); pp.device = ba; pp.channel = channel & 0xff;

  In the preceding example, deviceis set to a BT_ADDRtype that stores the remote device to initiate a remote connection over the RFCOMM layer.
  
  If the server channel is not known then the client can specify the UUID of the server in the uuidServicemember. In this case, an SDP query is performed automatically to retrieve the target channel number used on the remote device based on the service UUID.
  
  

Register the device by calling the RegisterDevicefunction, as the following example shows.

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HANDLE h = RegisterDevice (L"COM", index, L"btd.dll", (DWORD)&pp);

The preceding example specifies the port type as COM, port number, and the name of the device driver DLL, as parameters to RegisterDevice. Also, pass the address of PORTEMUPortParamsstructure, created in step 1, in the dwInfoparameter. RegisterDeviceregisters the Bluetooth Protocol stack with the virtual COM port.

Create a null-terminated string to store the name of the COM port. You must include a colon after the port name, as the following example shows.

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WCHAR szComPort[30]; wsprintf (szComPort, L"COM%d:", index);

Open the COM port by calling the CreateFilefunction.

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HANDLE hCommPort = CreateFile (szComPort, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);

To specify the port name, pass the string created in step 3, in the lpFileNameparameter of CreateFile.

For client ports, the physical connection is created only when the device is open with read or write access by using CreateFile. The physical connection is terminated for both server and client ports when the first handle with read or write access is closed.

Up to four open handles can be outstanding for each virtual port created. Every handle maintains its own set of communication event masks. If a file is open with a 0 access mask, it can only be used for WaitCommEvent, but not with ReadFileand WriteFileAPIs.

Call the CloseHandlefunction and pass the handle returned by CreateFile, as the following example code shows.

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CloseHandle (hCommPort);

To deregister the device, call the DeregisterDevicefunction and pass the handle returned by RegisterDevice, as the following example code shows.

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DeregisterDevice (h);

Set the channelmember of PORTEMUPortParamsto RFCOMM_CHANNEL_MULTIPLE.

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PORTEMUPortParams pp; memset (&pp, 0, sizeof(pp)); pp.channel = RFCOMM_CHANNEL_MULTIPLE;

Create the virtual COM port by using RegisterDeviceand CreateFile.

Determine the assigned RFCOMM channel by using the IOCTL, IOCTL_BLUETOOTH_GET_RFCOMM_CHANNEL.

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DWORD port = 0; DWORD dwSizeOut = 0; HANDLE hFile; if (!DeviceIoControl (hFile, IOCTL_BLUETOOTH_GET_RFCOMM_CHANNEL, NULL, 0, &port, sizeof(port), &dwSizeOut, NULL)) { // Perform error handling }