using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;

namespace PCI_Test
{ 
    class Program
    {
        [DllImport("adsapi32.dll", CharSet = CharSet.Auto)]
        public static extern System.Int32 DRV_DeviceOpen(System.UInt32 DeviceNum, ref System.Int32 DriverHandle);

        [DllImport("adsapi32.dll", CharSet = CharSet.Auto)]
        public static extern System.Int32 DRV_DeviceClose(ref System.Int32 DriverHandle);

        [DllImport("adsapi32.dll", CharSet = CharSet.Auto)]
        public static extern System.Int32 DRV_SelectDevice(IntPtr hCaller, System.Int32 GetModule, ref System.UInt32 DeviceNum, String Description);

        [DllImport("adsapi32.dll", CharSet = CharSet.Auto)]
        public static extern void DRV_GetErrorMessage(System.UInt32 ErrorCode, string ErrorMsg);

      	[DllImport( "User32.dll", CharSet=CharSet.Auto )]
        public static extern IntPtr GetDesktopWindow();

        [DllImport("adsapi32.dll", CharSet = CharSet.Auto)]
        public static extern  System.Int32 DRV_DeviceGetNumOfList ( IntPtr  NumOfDevices );

                
        [DllImport("adsapi32.dll", CharSet = CharSet.Auto)]
        public static extern System.Int32 AdxDioReadDiPorts(System.Int32 DriverHandle,
        System.UInt32 dwPortStart, System.UInt32 dwPortCount, IntPtr pBuffer);
   
     static unsafe void Main(string[] args)
        {          
            int lRezult;
            Int32 lDeviceNum =  0 ;
            Int32 NumOfDevices= 0 ;
            IntPtr hwndDesktop;
            string szDescription = new string(' ',  250 );
            UInt32 dwPortStart= 0 ;
            UInt32 dwPortCount= 1 ;
             IntPtr pBuffer;//<- указатель
            Int32 DriverHandle =  0 ;
            IntPtr a;
            lRezult = AdxDioReadDiPorts(DriverHandle, dwPortStart, dwPortCount, pBuffer);// <- здесь ошибка
        }
    }
}