一、什么是ModBus通讯协议
Modbus协议是应用于电子控制器上的一种通用语言，此协议支持传统的RS-232、RS-422、RS-485和以太网设备。
ModBus功能码
| 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 |
二、ModBus通讯协议的.Net实现
推荐一个github的开源实现类库：NModBus，github地址：https://github.com/NModbus/NModbus。针对TCP、UDP、RTU等的ModBus通讯方式都有实现。
读写方法：
| 方法名 | 作用 | 所需参数 | 返回值 | 对应功能码 |
| ReadCoils | 读取DO的状态 | 从站地址(8位) byte slaveAddress 起始地址(16位)
ushort startAddress 读取数量(16位) ushort numberOfPoints |
bool[] | 01 |
| ReadInputs | 读取DI的状态 | 从站地址(8位) byte slaveAddress 起始地址(16位)
ushort startAddress 读取数量(16位) ushort numberOfPoints |
bool[] | 02 |
| ReadHoldingRegisters | 读取AO的值 | 从站地址(8位) byte slaveAddress 起始地址(16位) ushort startAddress 读取数量(16位) ushort numberOfPoints |
ushort[] | 03 |
| ReadInputRegisters | 读取AI的值 | 从站地址(8 位) byte slaveAddress 起始地址(16位)
ushort startAddress 读取数量(16位) ushort numberOfPoints |
ushort[] | 04 |
| WriteSingleCoil | 写入值到DO | 从站地址(8位) byte slaveAddress 线圈地址(16位) ushort coilAddress 写入值(布尔型) bool value |
无返回值 | 05 |
| WriteSingleRegister | 写入值到AO | 从站地址(8位) byte slaveAddress 寄存器地址(16位) ushort registerAddress 写入值(16位) ushort value |
无返回值 | 06 |
| WriteMultipleCoils | 写多线圈寄存器 | 从站地址(8位) byte slaveAddress 起始地址(16位) ushort startAddress 写入值(布尔型数组) bool[] data |
无返回值 | 15 |
| WriteMultipleRegisters | 写多个保持寄存器 | 从站地址(8位) byte slaveAddress
起始地址(16位) ushort startAddress, 寄存器值(16位整型数组) ushort[] data |
无返回值 | 16 |
| ReadWriteMultipleRegisters | 读写多个保持寄存器 | 从站地址(8位) byte slaveAddress 读起始地址(16位) ushort startReadAddress
读取数量(16位) ushort numberOfPointsToRead, 写入起始地址(16位) ushort startWriteAddress, 写入值(16位整型数组) ushort[] writeData |
ushort[] | 23 |
每个方法都有各自的异步方法实现。
三、NModBus Master 示例
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private
static
void
Main(
string
[] args)
{
try
{
ModbusSerialRtuMasterWriteRegisters();
ModbusTcpMasterReadInputs();
}
catch
(Exception e)
{
Console.WriteLine(e.Message);
}
Console.WriteLine(
"Press any key to continue..."
);
Console.ReadKey();
}
/// <summary>
/// Simple Modbus serial RTU master write holding registers example.
/// </summary>
public
static
void
ModbusSerialRtuMasterWriteRegisters()
{
using
(SerialPort port =
new
SerialPort(
"COM3"
))
{
// configure serial port
port.BaudRate = 9600;
port.DataBits = 8;
port.Parity = Parity.None;
port.StopBits = StopBits.One;
port.Open();
var
factory =
new
ModbusFactory();
IModbusMaster master = factory.CreateRtuMaster(port);
byte
slaveId = 1;
ushort
startAddress = 100;
ushort
[] registers =
new
ushort
[] { 1, 2, 3 };
// write three registers
master.WriteMultipleRegisters(slaveId, startAddress, registers);
}
}
/// <summary>
/// Simple Modbus TCP master read inputs example.
/// </summary>
public
static
void
ModbusTcpMasterReadInputs()
{
using
(TcpClient client =
new
TcpClient(
"127.0.0.1"
, 502))
{
var
factory =
new
ModbusFactory();
IModbusMaster master = factory.CreateMaster(client);
// read five input values
ushort
startAddress = 100;
ushort
numInputs = 5;
bool
[] inputs = master.ReadInputs(0, startAddress, numInputs);
for
(
int
i = 0; i < numInputs; i++)
{
Console.WriteLine($
"Input {(startAddress + i)}={(inputs[i] ? 1 : 0)}"
);
}
}
// output:
// Input 100=0
// Input 101=0
// Input 102=0
// Input 103=0
// Input 104=0
}
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