.NET (Core and Framework)

<DllImport("CoreDll.dll")> _
Shared Function DeviceIoControl(ByVal hDevice As Integer, ByVal dwIoControlCode As Integer, _
                       ByVal lpInBuffer As String, ByVal nInBufferSize As Integer, _
                       ByVal lpOutBuffer() As Byte, ByVal nOutBufferSize As Integer, _
                       ByRef lpBytesReturned As Integer, ByVal lpOverlapped As Integer) As Integer
End Function

Private Declare Function CreateFile Lib "coredll.dll" _
                       (ByVal lpFileName As String, ByVal dwDesiredAccess As Int32, _
                        ByVal dwShareMode As Int32, ByVal lpSecurityAttributes As IntPtr, _
                        ByVal dwCreationDisposition As Int32, ByVal dwFlagsAndAttributes As Int32, _
                        ByVal hTemplateFile As IntPtr) As IntPtr

Declare Function CloseHandle Lib "coredll.dll" (ByVal hObject As IntPtr) As Boolean

Const FILE_SHARE_READ As Integer = &H1
Const FILE_SHARE_WRITE As Integer = &H2
Const GENERIC_READ As Integer = &H80000000
Const GENERIC_WRITE As Integer = &H40000000

Dim portPtr As IntPtr
Dim ris As Boolean
Dim InBuffer As String
Dim OutBuffer(100) As Byte
Dim BytesReturned, Overlapped As Int32

portPtr = CreateFile(com.PortName & ":", GENERIC_READ Or GENERIC_WRITE, FILE_SHARE_READ Or FILE_SHARE_WRITE, 0, OPEN_EXISTING, 0, 0)

ris = DeviceIoControl(portPtr.ToInt32, IOCTL_SERIAL_GET_COMMSTATUS, InBuffer, InBuffer.Length, OutBuffer, OutBuffer.Count, BytesReturned, Overlapped)

CloseHandle(portPtr)

#define IOCTL_SERIAL_GET_COMMSTATUS     CTL_CODE(FILE_DEVICE_SERIAL_PORT, 27, METHOD_BUFFERED, FILE_ANY_ACCESS)

typedef struct _SERIAL_STATUS {
  ULONG   Errors;
  ULONG   HoldReasons;
  ULONG   AmountInInQueue;
  ULONG   AmountInOutQueue;
  BOOLEAN EofReceived;
  BOOLEAN WaitForImmediate;
} SERIAL_STATUS, *PSERIAL_STATUS;