C# Signature:

  [StructLayout(LayoutKind.Sequential)]
  public struct SCARD_IO_REQUEST
  {
      public UInt32 dwProtocol;
      public UInt32 cbPciLength;
  }

[DllImport("winscard.dll")]
public static extern int SCardTransmit(
     IntPtr hCard,
     ref SCARD_IO_REQUEST pioSendRequest,
     ref byte SendBuff,
     UInt32 SendBuffLen,
     ref SCARD_IO_REQUEST pioRecvRequest,
     out byte RecvBuff,
     ref UInt32 RecvBuffLen
);

User-Defined Types:

None.

Notes:

None.

Tips & Tricks:

One may Get the SCARD_IO_REQUEST values which are defined as pointer to initialised data export in WinSCard.dll using the LoadLibrary and GetProcAddress pair.

If you use a struct rather than a class for SCARD_IO_REQUEST, don't forget to add "ref" to the pioRecvPci parameter in the signature. Alternatively, if you don't care about the returned protocol control information, change the pioRecvPci parameter to an "IntPtr" and pass "IntPtr.Zero" in as this parameter

Edit...

updated to better working signature (VS2010)...still need to establish context, and connect the card like in sample area, but this is an example of code that will read an iClass UID

    private int GetUID(ref byte[] UID)
    {
        byte[] receivedUID = new byte[10];
        UnsafeNativeMethods.SCARD_IO_REQUEST request = new UnsafeNativeMethods.SCARD_IO_REQUEST();
        request.dwProtocol = 1; //SCARD_PROTOCOL_T1);
        request.cbPciLength = System.Runtime.InteropServices.Marshal.SizeOf(typeof(UnsafeNativeMethods.SCARD_IO_REQUEST));
        byte[] sendBytes = new byte[] { 0xFF, 0xCA, 0x00, 0x00, 0x00 }; //get UID command for iClass cards

        int outBytes = receivedUID.Length;
        int status = SCardTransmit(_hCard, ref request, ref sendBytes[0], (uint)sendBytes.Length, ref request, out receivedUID[0], ref outBytes);

        UID = receivedUID.Take(8).ToArray(); //only take the first 8, the last 2 bytes are not part of the UID of the card (iClass 2k cards...not sure about others)
        return status;
    }

Sample Code:

// Paste here code for SCardEstablishContext, SCardConnect

[DllImport("kernel32.dll", SetLastError=true)]
private extern static IntPtr LoadLibrary(string lpFileName);

[DllImport("kernel32.dll")]
private extern static void FreeLibrary(IntPtr handle) ;

[DllImport("kernel32.dll")]
private extern static IntPtr GetProcAddress(IntPtr handle, string
procName);

//Get the address of Pci from "Winscard.dll".
private static IntPtr GetPciT0()
{
IntPtr handle = LoadLibrary("Winscard.dll") ;
IntPtr pci = GetProcAddress(handle, "g_rgSCardT0Pci") ;
FreeLibrary(handle) ;
return pci ;
}

SCARD_IO_REQUEST ioRecv = new SCARD_IO_REQUEST();
byte[] pbRecvBuffer=new byte [255];
int pcbRecvLength=255;
byte[] pbSendBuffer = { 0xC0, 0xA4, 0x00, 0x00, 0x02, 0x3F, 0x00 }; // Example Cla,Ins,P1,P2,P3,DataIN (Select MF)
int cbSendLength=pbSendBuffer.Length;
ioRecv.cbPciLength = 255;
IntPtr SCARD_PCI_T0 = PCSC.GetPciT0();
uint errors=SCardTransmit(nCard, SCARD_PCI_T0, pbSendBuffer, cbSendLength, ioRecv, pbRecvBuffer, ref pcbRecvLength);

// Paste here code for SCardDisconnect, pbRecvBuffer contains Answer as Byte[]

Alternative Managed API:

TODO