1：串口初始化

com = new SerialPort("COM3", 9600, Parity.Even, 7, StopBits.One);

2：打开关闭串口

if (com.IsOpen)

{com.Close();}

com.Open();

if (com.IsOpen)

{ com.Close();}

3：C# ASCII转字符及字符转ASCII

public static string Chr(int asciiCode)
        {
            if (asciiCode >= 0 && asciiCode <= 255)
            {
                System.Text.ASCIIEncoding asciiEncoding = new System.Text.ASCIIEncoding();
                byte[] byteArray = new byte[] { (byte)asciiCode };
                string strCharacter = asciiEncoding.GetString(byteArray);
                return (strCharacter);
            }
            else
            {
                throw new Exception("ASCII Code is not valid.");
            }

}

public static int Asc(string character)
        {
            if (character.Length == 1)
            {
                System.Text.ASCIIEncoding asciiEncoding = new System.Text.ASCIIEncoding();
                int intAsciiCode = (int)asciiEncoding.GetBytes(character)[0];
                return (intAsciiCode);
            }
            else
            {
                throw new Exception("Character is not valid.");
            }

}

4：写入串口的命令字符串的和校验

/// <summary>
        /// 和校验
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public string SumCheck(string data)
        {
            int sum = 0;
            for (int i = 0; i < data.Length; i++)
            {
                sum += Asc(data.Substring(i, 1));
            }

string res = sum.ToString("X");
            res = res.Substring(res.Length - 2, 2);

return res;

}

5：写入PLC

private void btnWrite_Click(object sender, EventArgs e)

{

string[] write = new string[] { "2","2"}; //将准备写入PLC的值
            //将要写入的值转换成16进制数,补齐两个字节,注意高低字节需要交换
            string sWriteData = "";
            for (int i = 0; i < write.Length; i++)
            {
                int val = Convert.ToInt32(write[i].Length>0?write[i]:"0");
                string s = val.ToString("X");
                while (s.Length<4)
                {
                    s = "0" + s;
                }
                sWriteData += s.Substring(2,2)+s.Substring(0,2);
            }

MessageBox.Show(sWriteData);
            //写入命令,1表示写入,1194表示D202这个地址的16进制,04表示D202,D203为4个BYTE,1194=(202*2)+4096的16进制数,至于用它表示D202的起始位置,三菱故意要这么麻烦了.
            sWriteData = "1119404" + sWriteData + Chr(3);
            //chr(2)和chr(3)是构成命令的标志字符,然后加上校验和,命令组织完成
            sWriteData = Chr(2) + sWriteData + SumCheck(sWriteData);

MessageBox.Show(sWriteData);
            //写入串口
            com.Write(sWriteData);
            //byte[] data = Encoding.ASCII.GetBytes(sWriteData); 
            //com.Write(data,0,data.Length);

}

6:读PLC

private void btnRead_Click(object sender, EventArgs e)
        {
            
            this.txtRead0.Clear();
            string sReadData = "";

//在读PLC中的数据之前,需要先发个指令给它,让它将数据发送到串口,下面的字符串中,chr(2),chr(3)为PLC命令的格式标志,0119404中,0表示读,1194表示D202的起始地址,04表示读D202,D203两个字,共4个字节,66为0119404和chr(3)的校验和,向串口写入"读"命令,其实和向plc地址中写入数据是一样的,只是没有数据,用0表示读

string sReadCmd = Chr(2) + "0119404" + Chr(3) + "66";
            com.Write(sReadCmd);
            //等待1秒钟
            System.Threading.Thread.Sleep(1000);
            // 从串口读数据
            byte[] data = new byte[1024];
            com.Read(data, 0, 1024);

//如果首位为2,则表示数据有效.这里有个问题,在第二次读,第2位才为'2',第三次又是首位为2,需要再测试
            if (data[0]==2)
            {
                string sReceiveData = System.Text.Encoding.ASCII.GetString(data);
                //MessageBox.Show(sReceiveData);
               //解析命令,将读到的字符解析成数字,注意高低位的转换
                for (int i = 1; i < 8; i += 4)
                {
                    string sLow = sReceiveData.Substring(i,2);
                    string sHigh = sReceiveData.Substring(i + 2, 2);
                    //int res = Convert.ToInt32(sHigh)+ Convert.ToInt32(sLow);
                    int res = Convert.ToInt32(sHigh,16) + Convert.ToInt32(sLow,16);

this.txtRead0.Text += res.ToString() + ",";
                }               
                
            }