What is Modbus?
Modbus protocol is applied to an electronic controller on the common language . By this protocol, between the controller, the controller can communicate via a network (e.g. Ethernet) and other devices. Modbus protocol defines a message structure that controllers will recognize that the use of whether they are communicating via which the network. It describes the process a controller requests access to other devices, if the response to requests from other devices, as well as how to detect and record errors. It developed a message domain structure and content of a common format .
Modbus is a request / response protocol
Modbus
The following are Modbus thermally decomposed to FIG.
Modbus message frame
Understand it, you will have a clear understanding of serial communication!
Universal message frame
ASCII message frame (8Bit each byte in the message are transmitted as two ASCII characters)
Hexadecimal, ASCII characters 0 ... 9, A ... F
Message each ASCII character is a hexadecimal character
Bits of each byte
A start bit
n data bits, the least significant bit sent
A parity bit, no parity no
1 (without parity) stop bit (when the check), Bit 2
Error detection domain
The LRC (vertical lengthy test)
RTU message frames
8-bit binary, hexadecimal 0 ... 9, A ... F
Each 8-bit message field is a two hexadecimal characters
Bits of each byte
A start bit
8 data bits, the least significant bit sent
A parity bit, no parity no
1 (without parity) stop bit (when the check), Bit 2
Error detection domain
CRC (cyclic redundancy detection)
CRC check ( http://baike.baidu.com/view/1664507.htm )
public static string CRCCheck(string val) { val = val.TrimEnd(' '); string[] spva = val.Split(' '); byte[] bufData = new byte[spva.Length + 2]; bufData = ToBytesCRC(val); ushort CRC = 0xffff; ushort POLYNOMIAL = 0xa001; for (int i = 0; i < bufData.Length - 2; i++) { CRC ^= bufData[i]; for (int j = 0; j < 8; j++) { if ((CRC & 0x0001) != 0) { CRC >>= 1; CRC ^= POLYNOMIAL; } else { CRC >>= 1; } } } return Maticsoft.DBUtility.HLConvert.ToHex(System.BitConverter.GetBytes(CRC)); } /// <summary> /// 例如把如下字符串转换成字节数组 /// AA AA AA AA 0A 00 68 00 06 03 04 54 21 28 22 E5 F3 16 BB BB BB BB 转换为字节数组 /// </summary> /// <param name="hex">十六进制字符串</param> /// <returns></returns> public static byte[] ToBytesCRC(string hex) { string[] temp = hex.Split(' '); byte[] b = new byte[temp.Length + 2]; for (int i = 0; i < temp.Length; i++) { b[i] = Convert.ToByte(temp[i], 16); } return b; } /// <summary> /// 将字节数据转换为十六进制字符串，中间用 “ ”分割 如：AA AA AA AA 0A 00 68 00 06 03 04 54 21 28 22 E5 F3 16 BB BB BB BB /// </summary> /// <param name="vars">要转换的字节数组</param> /// <returns></returns> public static String ToHex(byte[] vars) { return BitConverter.ToString(vars).Replace('-', ' ').Trim(); }CS校验(累加和)
public static string CSCheck(string str) { if (str.Length == 0) return ""; else str = str.Trim(); byte[] sss = ToBytes(str); int n = 0; for (int i = 0; i < sss.Length; i++) { n += sss[i]; } return ToHex(n); } /// <summary> /// AB CD 12 3B 转换为字节数组 /// </summary> /// <param name="hex">十六进制字符串</param> /// <returns></returns> public static byte[] ToBytes(string hex) { string[] temp = hex.Split(' '); byte[] b = new byte[temp.Length]; for (int i = 0; i < temp.Length; i++) { if (temp[i].Length > 0) b[i] = Convert.ToByte(temp[i], 16); } return b; } /// <summary> /// 转换为符合本程序的十六进制格式 /// </summary> /// <param name="var">1 2 3 等。</param> /// <returns>返回十六进制字符串，如果是1-9的话，前面带零</returns> /// <example>例如: 5 ="05" 12 ="0C" 无论何时，都是两位数。 </example> public static string ToHex(int var) { int cs = var; string tmp = ""; if (cs == 0) { tmp = "00"; } while (cs > 0) { int ys; cs = Math.DivRem(cs, 256, out ys); tmp = tmp.Insert(0, string.Format(" {0}", Right("00" + Convert.ToString(ys, 16), 2).ToUpper())); } return tmp.Trim(); } public static string Right(string str, int Length) { if ((Length <= 0) || (str == null)) { return ""; } int length = str.Length; if (Length >= length) { return str; } return str.Substring(length - Length, Length); }LRC校验(LRC错误校验用于ASCII模式)
/// <summary> /// 取模FF(255) /// 取反+1 /// </summary> /// <param name="writeUncheck"></param> /// <returns></returns> public static string LRCheck(string writeUncheck) { char[] hexArray = new char[writeUncheck.Length]; hexArray = writeUncheck.ToCharArray(); int decNum = 0, decNumMSB = 0, decNumLSB = 0; int decByte, decByteTotal = 0; bool msb = true; for (int t = 0; t <= hexArray.GetUpperBound(0); t++) { if ((hexArray[t] >= 48) && (hexArray[t] <= 57)) decNum = (hexArray[t] - 48); else if ((hexArray[t] >= 65) & (hexArray[t] <= 70)) decNum = 10 + (hexArray[t] - 65); if (msb) { decNumMSB = decNum * 16; msb = false; } else { decNumLSB = decNum; msb = true; } if (msb) { decByte = decNumMSB + decNumLSB; decByteTotal += decByte; } } decByteTotal = (255 - decByteTotal) + 1; decByteTotal = decByteTotal & 255; int a, b = 0; string hexByte = "", hexTotal = ""; double i; for (i = 0; decByteTotal > 0; i++) { b = Convert.ToInt32(System.Math.Pow(16.0, i)); a = decByteTotal % 16; decByteTotal /= 16; if (a <= 9) hexByte = a.ToString(); else { switch (a) { case 10: hexByte = "A"; break; case 11: hexByte = "B"; break; case 12: hexByte = "C"; break; case 13: hexByte = "D"; break; case 14: hexByte = "E"; break; case 15: hexByte = "F"; break; } } hexTotal = String.Concat(hexByte, hexTotal); } return hexTotal; } public void LRCheck(byte[] code) { int sum = 0; foreach (byte b in code) { sum += b; } sum = sum % 255;//取模FF(255) sum = ~sum + 1;//取反+1 string lrc = Convert.ToString(sum, 16); return lrc; }
Custom Modbus Datasheet
Modbus custom data table example:
Related equipment to read information:
Command message information analysis:
Custom Modbus data table definitions Note
Serial debugging tools
Serial use debugging tools.
+ RS485 serial debugging tools can read the data on the hardware, and the request to the hardware, how to use a detailed description see "Debugging chapter" will be.
Network debugging assistant:
Debugging assistant principal or TCP protocol communications in a debugging tool
