Exception thrown: Object reference not set to an instance of an object

[RShruthi]

namespace trial

{
class serial_function
{
Form1 p_form;
List<byte> Stepper_Respone_buffer = new List<byte>(1024); //1 page of memory is allocated by default, and the limit is always allowed to exceed
List<string> Stepper_Prase_buffer = new List<string>(10);
int received_count = 0;
string strPath = Application.StartupPath;
public static string cmd_backup;
public static string current_position = "0";
public int current_pos_backup = -1;
public static string Scaning_Runing_cmd;
public static string Scaning_gozero_cmd;
public static string Scaning_goposition_cmd;
public int count_get_current_position = 0;
public bool _isReceiving = false;
public bool _isbusy = false;
public int ini_step = 0;
public int need_send_scanning_cmd = 0;
public int need_send_gosposition_cmd = 0;
public int need_stop = 0;
public int need_gotohome = 0;
public static int gozero_still_flag = 0;


static string s;
public enum Data_type
{
No_Prase,
Prase_Status1,
Prase_Status2,
Prase_Status3,
Prase_Status,
Prase_Vaule,
Prase_Next_Value,

}

public Data_type Set_Data_type = Data_type.No_Prase;
public void Set_Cur_Data_type_Vaule()
{
Set_Data_type = Data_type.Prase_Vaule;
}
public void Set_Cur_Data_type_None()
{
Set_Data_type = Data_type.No_Prase;
}
public void Set_Cur_Data_type_Next_Value()
{
Set_Data_type = Data_type.Prase_Next_Value;
}

public void Set_Scaning_Run_Ntime(string cmd)
{
Set_Data_type = Data_type.Prase_Next_Value;
Scaning_Runing_cmd = cmd;
need_send_scanning_cmd = 1;
}

public void Set_Scaning_Go_Zero(string cmd)
{
Set_Data_type = Data_type.Prase_Next_Value;
Scaning_gozero_cmd = cmd;
need_send_scanning_cmd = 1;
}

public void Set_Scaning_Go_sposition(string cmd)
{
Set_Data_type = Data_type.Prase_Next_Value;
Scaning_goposition_cmd = cmd;
need_send_gosposition_cmd = 1;
}

public void Set_Form(Form1 form)
{
p_form = form;
}
/*
* Get the serial port list of this machine
*/
public void GetComList()
{
try
{
RegistryKey keyCom = Registry.LocalMachine.OpenSubKey("Hardware\\DeviceMap\\SerialComm");
if (keyCom != null)
{
string[] sSubKeys = keyCom.GetValueNames();
//p_form.comboBox1.Items.Clear();
foreach (string sName in sSubKeys)
{
string sValue = (string)keyCom.GetValue(sName);
//cb.Items.Add(sValue);
p_form.comboBox1.Items.Add(sValue);
}
if (p_form.comboBox1.Items.Count >= 1)
p_form.comboBox1.SelectedIndex = 0;
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}
/*
* Open serial port
*/
public void Serial_Port_Open(string portname)
{
try
{
if (p_form.btn_connect.Text == "Connect")
{
p_form.serialPort1.PortName = portname;
p_form.serialPort1.BaudRate = 9600;
p_form.serialPort1.DataBits = 8;
p_form.serialPort1.StopBits = StopBits.One;
p_form.serialPort1.Parity = Parity.None;
p_form.serialPort1.WriteTimeout = 1000;
p_form.serialPort1.ReadTimeout = 1000;
p_form.serialPort1.ReadBufferSize = 256;
if (!p_form.serialPort1.IsOpen)
{
p_form.serialPort1.Open();
p_form.serialPort1.DataReceived += new SerialDataReceivedEventHandler(serialPort1_DataReceived);
p_form.serialPort1.ReceivedBytesThreshold = 1;
//Get_Stepper_Respone_Thread = new Thread(Get_Stepper_Respone_Function);
// Get_Stepper_Respone_Thread.IsBackground = true;
// Get_Stepper_Respone_Thread.Start();
Set_Data_type = Data_type.Prase_Status3;
Serial_Port_Send_Cmd("/" + Prase_Calibration_file.Add.ToString() +
"m" + Prase_Calibration_file.MoveCrnt.ToString() +
"h" + Prase_Calibration_file.HoldCrnt.ToString() +
"f" + Prase_Calibration_file.OptoFlag.ToString() + "R\r");
}
else
{
Set_Data_type = Data_type.Prase_Status3;
Serial_Port_Send_Cmd("/" + Prase_Calibration_file.Add.ToString() + "h" + Prase_Calibration_file.HoldCrnt.ToString() + "f" + Prase_Calibration_file.OptoFlag.ToString() + "R\r");

}
}
else
{
p_form.btn_connect.Text = "Connect";
p_form.status_check.Text = "Not connected";
p_form.status_check.ForeColor = Color.Red;
Serial_Port_Close();

}
}
catch (Exception ex)
{
Serial_Port_Close();
MessageBox.Show("Com Port \n" + portname + "\" Open Failed!\r\n" + ex.Message, "Open", MessageBoxButtons.OK, MessageBoxIcon.Error);

}
}
/*
* Close the serial port
*/
public void Serial_Port_Close()
{
p_form.serialPort1.DataReceived -= serialPort1_DataReceived; //Exception thrown
int i = Environment.TickCount;
while (Environment.TickCount - i < 2000 && _isReceiving == true)
Application.DoEvents();
p_form.serialPort1.Close();
}
/*
* Serial port receiving data entry
*/
public void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
_isReceiving = true;
p_form.send_cmd_count = 0;
try
{
Thread.Sleep(50);
int n = p_form.serialPort1.BytesToRead;
if (n <= 0)
return;
byte[] readBuffer = new byte[n];
p_form.serialPort1.Read(readBuffer, 0, n);
received_count += n;//Increase the receive count
//1.Cache data
Stepper_Respone_buffer.AddRange(readBuffer);
//2.Integrity judgment
for (int i = 0; i < Stepper_Respone_buffer.Count; i++)
{
Stepper_Prase_buffer.Add(Stepper_Respone_buffer.ToString("X2"));

}
s = string.Join(" ", Stepper_Prase_buffer.ToArray());

if (Prase_Calibration_file.Logstatusflag == 1)
{
p_form.loginfo.Loginfo(strPath + "/Logs/Log", "receive data " + s);
}



if (Stepper_Respone_buffer[3] == 0x60) //0x60= 96

p_form.Statusready(Prase_Calibration_file.Add.ToString());


else

p_form.Statusbusy(Prase_Calibration_file.Add.ToString());




Stepper_Prase_buffer.Clear();
while (Stepper_Respone_buffer.Count >= 6)
{
int index = Stepper_Respone_buffer.FindIndex((delegate(byte d) { return d == 0x03; }));
if (Stepper_Respone_buffer[0] == 0xFF &&
Stepper_Respone_buffer[1] == 0x2F &&
index > 3 &&
Stepper_Respone_buffer[index + 1] == 0x0D &&
Stepper_Respone_buffer[index + 2] == 0x0A)
{



byte[] readdata = new byte[index + 3];
Stepper_Respone_buffer.CopyTo(0, readdata, 0, index + 3);
Serial_Data_Prase(readdata, index + 3);
Stepper_Respone_buffer.RemoveRange(0, index + 3);
received_count -= index + 3;


}

else
{

Thread.Sleep(150);
Serial_Port_Send_Cmd("/" + Prase_Calibration_file.Add.ToString() + "?0\r");
Set_Data_type = Data_type.Prase_Vaule;
break;
}
}
Stepper_Respone_buffer.RemoveRange(0, received_count);//Receiving an erroneous data also requires removing the data from the cache.
received_count = 0;
_isReceiving = false;
}
catch
{
Stepper_Respone_buffer.RemoveRange(0, received_count);//Receiving an erroneous data also requires removing the data from the cache
received_count = 0;
_isReceiving = false;
}
}


/*
* Send commands to the motor drive
*/
public void Serial_Port_Send_Cmd(string cmd)
{
try
{
p_form.send_cmd_count++;

cmd_backup = cmd;

if (Prase_Calibration_file.Logstatusflag == 1)
{
p_form.loginfo.Loginfo(strPath + "/Logs/Log", "sent cmd" + cmd_backup + "\n");
}

p_form.serialPort1.WriteLine(cmd);

}
catch (Exception ex)
{
MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}



This code block is to open and connect to a COM port and make the stepper motor to drive through PC. I have this code for a different application and i am using this the same code for another similar application. While i changed the code in the application working part, this code remains untouched since it is to get serial port and make a connection. However exception is thrown and i have no idea where it is wrong. Thank you in Advance.

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