I2C communication PCF8574AP

sorry, i don’t know how to read a register… in NXC i did it that:

void writeReg(byte reg)
{
 byte buff[] = {0x70, 0x00};
 buff[1] = reg;
 int nbytes;
 I2CWrite(I2C, 0, buff);
 while(I2CStatus(I2C, nbytes) == STAT_COMM_PENDING);
 Wait(100);
}

because i need only outputs and that is working fine, but i need it in C# on EV3. Maybe i’m doing something wrong? Here is my code…
Main.cs

using System;
using System.Threading;
using MonoBrickFirmware;
using MonoBrickFirmware.Display.Dialogs;
using MonoBrickFirmware.Display;
using MonoBrickFirmware.Sensors;
using MonoBrickFirmware.UserInput;

namespace test
{
	class MainClass
	{
		public static void Main (string[] args)
		{
			EventWaitHandle stopped = new ManualResetEvent (false);
			ButtonEvents btn = new ButtonEvents ();
			byte address = 0x70;
			byte[] data1 = new byte[8] {1, 1, 1, 1, 1, 1, 1, 1};
			byte[] data0 = new byte[8] {0, 0, 0, 0, 0, 0, 0, 0};
			LcdConsole.WriteLine ("hello world!");
			pcf pcf = new pcf (SensorPort.In1, address);
			btn.EscapePressed += () => {
				LcdConsole.WriteLine("stopped");
				stopped.Set ();
			};
			btn.LeftPressed += () => {
				pcf.WriteReg(0, data1);
				LcdConsole.WriteLine("write data1");
			};
			btn.RightPressed += () => {
				pcf.WriteReg(0, data0);
				LcdConsole.WriteLine("write data0");
			};
			stopped.WaitOne ();
		}
	}
}

pcf.cs

using System;
using MonoBrickFirmware;
using MonoBrickFirmware.Sensors;

namespace test
{
	public class pcf : I2CSensor
	{
		public pcf (SensorPort Port, byte adress) : base (Port, adress, I2CMode.LowSpeed)
		{
			base.Initialise();
		}

		public byte[] ReadReg(byte Register, byte Length)
		{
			return base.ReadRegister(Register, Length);
		}

		public void WriteReg(byte Register, byte[] Data)
		{
			base.WriteRegister(Register, Data);
		}

		public byte[] ReadAndWriteReg(byte Register, byte[] Data, int rxLength)
		{
			return base.WriteAndRead(Register, Data, rxLength);
		}

		public override string ReadAsString()
		{
			throw new NotImplementedException();
		}

		public override void SelectNextMode()
		{
			throw new NotImplementedException ();
		}

		public override string GetSensorName()
		{
			return "PCF8574AP";
		}

		public override void SelectPreviousMode()
		{
			throw new NotImplementedException ();
		}

		public override int NumberOfModes()
		{
			return 0;
		}

		public override string SelectedMode()
		{
			return "0";
		}
	}
}

unfortunetly, it is not workking… i found source of sending function

               /// <summary>
		/// Write and read an array of bytes to the sensor
		/// </summary>
		/// <returns>The bytes that was read</returns>
		/// <param name="register">Register to write to.</param>
		/// <param name="data">Byte array to write</param>
		/// <param name="rxLength">Length of the expected reply</param>
        protected byte[] WriteAndRead (byte register, byte[] data, int rxLength)
		{
			if (rxLength > BufferSize)
				throw new ArgumentOutOfRangeException("I2C Receive Buffer only holds " + BufferSize + " bytes");
			if (data.Length > BufferSize) {
				throw new ArgumentOutOfRangeException("I2C Write Buffer only holds " + BufferSize + " bytes");
			}
			bool dataReady = false;
			int replyIndex = 0;
			byte[] writeData = new byte[BufferSize];//30
			Array.Copy (data, 0, writeData, 0, data.Length);
			ByteArrayCreator command = new ByteArrayCreator ();
			command.Append ((int)-1);
			command.Append ((byte)this.port);
			command.Append ((byte)1);//repeat
			command.Append ((short)0);//time
			command.Append ((byte)(data.Length + 2));//length of write data
			command.Append ((byte)((byte)I2CAddress >> 1));
			command.Append (register);
			command.Append(writeData);
			command.Append ((byte)-rxLength);
			replyIndex = command.Data.Length;
			command.Append (new byte[BufferSize]);//make room for reply
			byte[] i2cData = command.Data;
			while (!dataReady) {
				unchecked {
					I2CDevice.IoCtl ((Int32)I2CIOSetup, i2cData);
				}
				int status = BitConverter.ToInt32 (i2cData, 0);
				if (status < 0) {
					throw new Exception ("I2C I/O error");
				}
				if (status == 0) {
					byte[] reply = new byte[rxLength];
					if (rxLength > 0) {
						Array.Copy(i2cData,replyIndex, reply,0, rxLength);
					}
					return reply;
				}
			}
        	throw new TimeoutException("I2C timeout");
    	}

maybe this should help…

in datasheet for PCF8574A address is
0 1 1 1 A2 A1 A0 0
and my A2, A1, A0 is 0, so b01110000 = 0x70. i should read bytes, but i need only write bits… i don’t understand too much…

ok, i did that:
LcdConsole.WriteLine(BitConverter.ToString(pcf.ReadReg(2, 1)));
and i got “03” on lcd when i connect P0 to + and “02” when i connect P0 to -. So, register is just a number of port to read/write?