关于串口程序的问题,

我要写一个串口程序,要求运行在ARM开发板上,WINCE系统.代码如下:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;using System.IO.Ports; namespace test_tx
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        int a = 0;
        int c = 0;
        private void button1_Click(object sender, EventArgs e)
        {
            //发送
            serialPort1.Open();
            a = a + 1; if (a == 10) { a = 0; }
            serialPort1.WriteLine(a.ToString());
            textBox2.Text = " 发送" + a; 
        }
       private void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            c = serialPort1.ReadChar();
            serialPort1.Close();
            c = c - 48;
            textBox1.Text = " 收到" + c;
       }
        private void textBox1_TextChanged(object sender, EventArgs e)
        {       }
       private void textBox2_TextChanged(object sender, EventArgs e)
        {       }
        private void Form1_Load(object sender, EventArgs e)
        {
           serialPort1.PortName = "COM1";
            serialPort1.BaudRate = 9600;
           serialPort1.Parity = Parity.None;
           serialPort1.DataBits = 8;
           serialPort1.StopBits = StopBits.One;
           serialPort1.RtsEnable = true;
            serialPort1.DtrEnable = true;
            serialPort1.ReadTimeout = 1000;            serialPort1.ReceivedBytesThreshold = 2;
            serialPort1.DataReceived += new System.IO.Ports.SerialDataReceivedEventHandler(this.serialPort1_DataReceived);        }    }
}生成的EXE文件在PC机WINXP系统上运行正常,在短接COM口后可以收到数;但在ARM开发板WINCE系统下总是报错,撤掉短接线后不报错了,所以怀疑是接收时出了问题,请大家指点一下.