Use of Nmodbus

In a recent project, we need to use Modbus RTU to communicate with PLC, and now we will use the process record for future reference.

First, what is the Modbus communication protocol

The Modbus protocol is a common language applied to electronic controllers that supports traditional RS-232, RS-422, RS-485, and Ethernet devices.

Modbus function code

01	READ COIL STATUS
02	READ INPUT STATUS
03	READ HOLDING REGISTER
04	READ INPUT REGISTER
05	WRITE single COIL
06	WRITE single REGISTER
15	WRITE multiple COIL
16	WRITE multiple REGISTER

Ii.. NET implementation of Modbus communication protocol

Because the implementation is not difficult, there are many online users of their own implementation, but here I recommend a github open Source implementation class Library: Nmodbus4,github address: HTTPS://GITHUB.COM/NMODBUS4/NMODBUS4. For TCP, UDP, RTU and other Modbus communication methods have been implemented.

Read and Write methods:

Method name	Role	Required Parameters	return value	corresponding function code
Readcoils	Read the status of Do	Slave address (8-bit) BYTE slaveaddress Start address (16-bit) UShort Startaddress Number of reads (16-bit) UShort Numberofpoints	Bool[]	01
Readinputs	Read the state of Di	Slave address (8-bit) BYTE slaveaddress Start address (16-bit) UShort Startaddress Number of reads (16-bit) UShort Numberofpoints	Bool[]	02
Readholdingregisters	Read the value of AO	Slave address (8-bit) BYTE slaveaddress Start address (16-bit) UShort Startaddress Number of reads (16-bit) UShort Numberofpoints	Ushort[]	03
Readinputregisters	Read the value of AI	Slave address (8-bit) BYTE slaveaddress Start address (16-bit) UShort Startaddress Number of reads (16-bit) UShort Numberofpoints	Ushort[]	04
Writesinglecoil	Write value to do	Slave address (8-bit) BYTE slaveaddress Coil Address (16-bit) UShort Coiladdress Write Value (Boolean) BOOL Value	No return value	05
Writesingleregister	Write value to AO	Slave address (8-bit) BYTE slaveaddress Register address (16-bit) UShort Registeraddress Write value (16-bit) UShort Value	No return value	06
Writemultiplecoils	Write multi-coil registers	Slave address (8-bit) BYTE slaveaddress Start address (16-bit) UShort Startaddress Write value (Boolean array) Bool[] Data	No return value	15
Writemultipleregisters	Write multiple hold Registers	Slave address (8-bit) BYTE slaveaddress Start address (16-bit) UShort Startaddress, Register value (16-bit integer array) Ushort[] Data	No return value	16
Readwritemultipleregisters	Read and write multiple hold registers	Slave address (8-bit) BYTE slaveaddress Read start address (16-bit) UShort Startreadaddress Number of reads (16-bit) UShort Numberofpointstoread, Write start address (16-bit) UShort Startwriteaddress, Write value (16-bit integer array) Ushort[] WriteData	Ushort[]	23

Each method has its own asynchronous method implementation.

Here is an RTU to show how to use it:

1 /// <summary>
 2 /// Create a ModBus RTU connection
 3 /// </summary>
 4 /// <param name="portName">port number</param>
 5 /// <param name="baudRate">Baud rate</param>
 6 /// <param name="parity">parity bit </param>
 7 /// <param name="dataBits">data bits</param>
 8 /// <param name="stopBits">stop bit</param>
 9 /// <returns></returns>
10 public IModbusSerialMaster CreateModBusRtuConnection(string portName, int baudRate, Parity parity, int dataBits, StopBits stopBits)
11 {
12 return CreateModBusRtuConnect(new SerialPort(portName, baudRate, parity, dataBits, stopBits));
13 }
14
15 public IModbusSerialMaster CreateModBusRtuConnection(SerialPort serialPort)
16 {
17 IModbusSerialMaster master = null;
18 if (!serialPort.IsOpen)
19 {
20 try
twenty one                 {
22 serialPort.Open();
twenty three                 }
24 catch (Exception e)
25 {
26 throw e;
27 }
28 }
29 try
30 {
31 master = ModbusSerialMaster.CreateRtu(serialPort);
32 /// can also configure some parameters of the master
33 master.Transport.ReadTimeout = 100; / / read data timeout 100ms
34 master.Transport.WriteTimeout = 100; / / write data timeout 100ms
35 master.Transport.Retries = 3;//Retry times
36 master.Transport.WaitToRetryMilliseconds = 10;//Retry interval
37
38 }
39 catch(Exception e)
40 { throw e;
41 }
42 return master;
43 }
44 }

View Code

Use of Nmodbus