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Modbus

The Modbus projects are comprised of a library, a console application, a test project, and two web applications.

ModbusLib

The Modbus library provides a set of helper classes to facilitate data access to a Modbus slave. This library is using the NModbus library (found at GitHub (https://github.com/NModbus/NModbus) and has been recompiled as a .NET Standard 2.0 library.

NModbus

NModbus is a fork of NModbus4 which itself is a fork of the original NModbus (https://code.google.com/p/nmodbus) and supports serial ASCII, serial RTU, TCP, and UDP protocols. NModbus is a C# implementation of the Modbus protocol. Here only the Modbus TCP master is used to communicate with the Modbus TCP slaves.

The APIs used are:

Function Function Code
Read Discrete Inputs (fc 2)
Read Coils (fc 1)
Write Single Coil (fc 5)
Write Multiple Coils (fc 15)
Read Input Registers (fc 4)
Read Multiple Registers (fc 3)
Write Single Register (fc 6)
Write Multiple Registers (fc 16)

Modbus Conversion

The additional datatypes supported are:

  • BitArray
  • Short
  • UShort
  • Int32
  • UInt32
  • Float
  • Double
  • Long
  • ULong
  • ASCII
  • Hex

Conversion routines from and to Modbus registers are provided.

NModbus Extensions

Additonal data types (using read/write coils and holding registers) are supported:

Function Description
ReadString Reads an ASCII string (multiple holding registers)
ReadHexString Reads an HEX string (multiple holding registers)
ReadBool Reads a boolean value (single coil)
ReadBits Reads a 16 bit array (single holding register)
ReadShort Reads a 16 bit integer (single holding register)
ReadUShort Reads an unsigned 16 bit integer (single holding register)
ReadInt32 Reads a 32 bit integer (two holding registers)
ReadUInt32 Reads an unsigned 32 bit integer (two holding registers)
ReadFloat Reads a 32 bit IEEE floating point number (two holding registers)
ReadDouble Reads a 64 bit IEEE floating point number (four holding registers)
ReadLong Reads a 64 bit integer (four holding registers)
ReadULong Reads an unsigned 64 bit integer (four holding registers)
ReadBoolArray Reads an array of boolean values (multiple coils)
ReadBytes Reads 8 bit values (multiple holding register)
ReadShortArray Reads an array of 16 bit integers (multiple holding register)
ReadUShortArray Reads an array of unsigned 16 bit integer (multiple holding register)
ReadInt32Array Reads an array of 32 bit integers (multiple holding registers)
ReadUInt32Array Reads an array of unsigned 32 bit integers (multiple holding registers)
ReadFloatArray Reads an array of 32 bit IEEE floating point numbers (multiple holding registers)
ReadDoubleArray Reads an array of 64 bit IEEE floating point numbers (multiple holding registers)
ReadLongArray Reads an array of 64 bit integers (multiple holding registers)
ReadULongArray Reads an array of unsigned 64 bit integers (multiple holding registers)
WriteString Writes an ASCII string (multiple holding registers)
WriteHexString Writes an HEX string (multiple holding registers)
WriteBool Writes a boolean value (single coil)
WriteBits Writes a 16 bit array (single holding register)
WriteShort Writes a 16 bit integer (single holding register)
WriteUShort Writes an unsigned 16 bit integer (single holding register)
WriteInt32 Writes a 32 bit integer (two holding registers)
WriteUInt32 Writes an unsigned 32 bit integer (two holding registers)
WriteFloat Writes a 32 bit IEEE floating point number (two holding registers)
WriteDouble Writes a 64 bit IEEE floating point number (four holding registers)
WriteLong Writes a 64 bit integer (four holding registers)
WriteULong Writes an unsigned 64 bit integer (four holding registers)
WriteBoolArray Writes an array of boolean values (multiple coils)
WriteBytes Writes 8 bit values (multiple holding register)
WriteShortArray Writes an array of 16 bit integers (multiple holding register)
WriteUShortArray Writes an array of unsigned 16 bit integer (multiple holding register)
WriteInt32Array Writes an array of 32 bit integers (multiple holding registers)
WriteUInt32Array Writes an array of unsigned 32 bit integers (multiple holding registers)
WriteFloatArray Writes an array of 32 bit IEEE floating point numbers (multiple holding registers)
WriteDoubleArray Writes an array of 64 bit IEEE floating point numbers (multiple holding registers)
WriteLongArray Writes an array of 64 bit integers (multiple holding registers)
WriteULongArray Writes an array of unsigned 64 bit integers (multiple holding registers)

Additonal data types (read discrete inputs and input registers) are supported:

Function Description
ReadOnlyString Reads an ASCII string (multiple input registers)
ReadOnlyHexString Reads an HEX string (multiple input registers)
ReadOnlyBool Reads a boolean value (single discrete input)
ReadOnlyBits Reads a 16 bit array (single holding register)
ReadOnlyShort Reads a 16 bit integer (single holding register)
ReadOnlyUShort Reads an unsigned 16 bit integer (single input register)
ReadOnlyInt32 Reads a 32 bit integer (two input registers)
ReadOnlyUInt32 Reads an unsigned 32 bit integer (two input registers)
ReadOnlyFloat Reads a 32 bit IEEE floating point number (two input registers)
ReadOnlyDouble Reads a 64 bit IEEE floating point number (four input registers)
ReadOnlyLong Reads a 64 bit integer (four input registers)
ReadOnlyULong Reads an unsigned 64 bit integer (four input registers)
ReadOnlyBoolArray Reads an array of boolean values (multiple discrete inputs)
ReadOnlyBytes Reads 8 bit values (multiple input register)
ReadOnlyShortArray Reads an array of 16 bit integers (multiple input register)
ReadOnlyUShortArray Reads an array of unsigned 16 bit integer (multiple input register)
ReadOnlyInt32Array Reads an array of 32 bit integers (multiple input registers)
ReadOnlyUInt32Array Reads an array of unsigned 32 bit integers (multiple input registers)
ReadOnlyFloatArray Reads an array of 32 bit IEEE floating point numbers (multiple input registers)
ReadOnlyDoubleArray Reads an array of 64 bit IEEE floating point numbers (multiple input registers)
ReadOnlyLongArray Reads an array of 64 bit integers (multiple input registers)
ReadOnlyULongArray Reads an array of unsigned 64 bit integers (multiple input registers)

Modbus Attribute

This attribute allows to mark a property with a Modbus specific offset, length, and access mode.

    [Modbus(1)]
    public ushort Value { get; set; }

    [Modbus(1, AccessModes.ReadOnly)]
    public ushort Value { get; set; }

    [Modbus(1, AccessModes.ReadOnly, 4)]
    public long Value { get; set; }

    [Modbus(offset: 1, access: AccessModes.ReadOnly, length: 4)]
    public double Value { get; set; }

Those attributes can be used to access the actual modbus registers (at the specified offset, using the specified numbers).

ModbusApp

The NModbus console application is used to access Modbus slave devices over ethernet (TCP) or serial lines (RTU). Several commandline options are provided to facilitate the device access and optionally to override settings from the JSON configuration file ("appsettings.json"). All commands have -? and --help options to display usage information.

Root Command

Option Description
--verbose Shows the current settings (typically from "appsettings.json")
--config Shows the all configuration items (environment, settings, etc.)

The root command option --verbose can also be used in all sub commands.

Command Description
rtu Supporting standard Modbus RTU operations
tcp Supporting standard Modbus TCP operations

rtu Command

Option Description
--com <string> Sets the Modbus master COM port
--baudrate <number> Sets the Modbus COM port baud rate
--parity <string> Sets the Modbus COM port parity
--databits <number> Sets the Modbus COM port data bits
--stopbits <string> Sets the Modbus COM port stop bits
--slaveid <number> Sets the Modbus slave ID
--read-timeout <number> Sets the timeout in msec (hidden)
--write-timeout <number> Sets the timeout in msec (hidden)

The rtu command options can also be used in the following sub commands.

Command Description
read Supporting standard Modbus RTU read operations
write Supporting standard Modbus RTU write operations
monitor Supporting standard Modbus RTU monitor operations

read Command

Option Description
-c --coil Reads coil(s)
-d --discrete Reads discrete input(s)
-h --holding Reads holding register(s)
-i --input Reads input register(s)
-x --hex Displays the register values in HEX
-n --number <number> The number of items to read
-o --offset <number> The offset of the first item to read
-t --type <string> Reads the specified data type

write Command

Option Description
-c --coil <json> Writes coil(s)
-h --holding <json> Writes holding register(s)
-x --hex Writes the HEX values (string)
-o --offset <number> The offset of the first item to write
-t --type <string> Writes the specified data type

monitor Command

Option Description
-c --coil Reads coil(s)
-d --discrete Reads discrete input(s)
-h --holding Reads holding register(s)
-i --input Reads input register(s)
-x --hex Displays the register values in HEX
-n --number <number> The number of items to read
-o --offset <number> The offset of the first item to read
-t --type <string> Reads the specified data type
-r --repeat <number> The number of times to read
-s --seconds <number>> The number of seconds between reads

The monitor command runs for the number of times specified and can be terminated using Control-C.

tcp Command

Option Description
--address <string> Sets the Modbus slave IP address
--port <number> Sets the Modbus slave port number
--slaveid <number> Sets the Modbus slave ID
--receive-timeout <number> Sets the timeout in msec (hidden)
--send-timeout <number> Sets the timeout in msec (hidden)

The tcp command options can also be used in the following sub commands.

Command Description
read Supporting standard Modbus TCP read operations
write Supporting standard Modbus TCP write operations
monitor Supporting standard Modbus TCP monitor operations

read Command

Option Description
-c --coil Reads coil(s)
-d --discrete Reads discrete input(s)
-h --holding Reads holding register(s)
-i --input Reads input register(s)
-x --hex Displays the register values in HEX
-n --number <number> The number of items to read
-o --offset <number> The offset of the first item to read
-t --type <string> Reads the specified data type

write Command

Option Description
-c --coil <json> Writes coil(s)
-h --holding <json> Writes holding register(s)
-x --hex Writes the HEX values (string)
-o --offset <number> The offset of the first item to write
-t --type <string> Writes the specified data type

monitor Command

Option Description
-c --coil Reads coil(s)
-d --discrete Reads discrete input(s)
-h --holding Reads holding register(s)
-i --input Reads input register(s)
-x --hex Displays the register values in HEX
-n --number <number> The number of items to read
-o --offset <number> The offset of the first item to read
-t --type <string> Reads the specified data type
-r --repeat <number> The number of times to read
-s --seconds <number>> The number of seconds between reads

The monitor command runs for the number of times specified and can be terminated using Control-C.

ModbusRTU

The ModbusRTU web application is used to access Modbus RTU slave devices providing a REST based web service. The Web service can act as a HTTP gateway to Modbus slave devices providing a common well known protocol and the use of JSON for the data exchange.

The Web API page provides a common Web interface for the REST web API using Swagger. The configuration is stored in the appsettings.json file.

appsettings.json

The typical configuration file contains application settings, the database connection string and the Serilog logger settings. The TcpSlave settings allow to specifiy the Modbus TCP slave device.

{
  "AppSettings": {
    "RtuMaster": {
      "SerialPort": "COM1",
      "Baudrate": 19200,
      "ReadTimeout": 10000,
      "WriteTimeout": 10000
    },
    "RtuSlave": {
      "ID": 1
    }
  },
  "Serilog": {...}
  },
  "AllowedHosts": "*"
}

ModbusTCP

The ModbusTCP web application is used to access Modbus TCP slave devices providing a REST based web service. The Web service can act as a HTTP gateway to Modbus slave devices providing a common well known protocol and the use of JSON for the data exchange.

The Web API page provides a common Web interface for the REST web API using Swagger. The configuration is stored in the appsettings.json file.

appsettings.json

The typical configuration file contains application settings, the database connection string and the Serilog logger settings. The RtuMaster and RtuSlave settings allow to specifiy the Modbus RTU master and slave device.

{
  "AppSettings": {
    "TcpSlave": {
      "Address": "10.0.1.77",
      "Port": 502,
      "ID": 1
    }
  },
  "Serilog": {...}
  },
  "AllowedHosts": "*"
}

REST Web API

Coils & Discrete Inputs

HTTP Address Description
GET /Coil/{offset} Reading a single coil from a Modbus slave.
PUT /Coil/{offset} Writing a single coil to a Modbus slave.
GET /Coils/{offset} Reading multiple coils from a Modbus slave.
PUT /Coils/{offset} Writing multiple coils to a Modbus slave.
GET /DiscreteInput/{offset} Reading a single discrete input from a Modbus slave.
GET /DiscreteInputs/{offset} Reading multiple discrete inputs from a Modbus slave.

Holding & Input Registers

HTTP Address Description
GET /HoldingRegister/{offset} Reading a single holding register from a Modbus slave.
PUT /HoldingRegister/{offset} Writing a single holding registers to a Modbus slave.
GET /HoldingRegisters/{offset} Reading multiple holding registers from a Modbus slave.
PUT /HoldingRegisters/{offset} Writing multiple holding registers to a Modbus slave.
GET /InputRegister/{offset} Reading a single input register from a Modbus slave.
GET /InputRegisters/{offset} Reading multiple input registers from a Modbus slave.

Boolean Data Values

HTTP Address Description
GET /ROArray/Bool/{offset} Reads an array of boolean values from a Modbus slave.
GET /ROSingle/Bool/{offset} Reads a boolean value from a Modbus slave.
GET /RWArray/Bool/{offset} Reads an array of boolean values from a Modbus slave.
PUT /RWArray/Bool/{offset} Writes an array of boolean values to a Modbus slave.
GET /RWSingle/Bool/{offset} Reads a boolean value from a Modbus slave.
PUT /RWSingle/Bool/{offset} Writes a boolean value to a Modbus slave.

8-Bit Data Values

HTTP Address Description
GET /ROArray/Bytes/{offset} Reads 8-bit values from a Modbus slave.
GET /RWArray/Bytes/{offset} Reads 8-bit values from a Modbus slave.
PUT /RWArray/Bytes/{offset} Writes 8-bit values to a Modbus slave.

Short Data Values

HTTP Address Description
GET /ROArray/Short/{offset} Reads an array of 16 bit integers from a Modbus slave.
GET /ROSingle/Short/{offset} Reads a 16 bit integer from a Modbus slave.
GET /RWArray/Short/{offset} Reads an array of 16 bit integers from a Modbus slave.
PUT /RWArray/Short/{offset} Writes an array of 16 bit integers to a Modbus slave.
GET /RWSingle/Short/{offset} Reads a 16 bit integer from a Modbus slave.
PUT /RWSingle/Short/{offset} Writes a 16 bit integer to a Modbus slave.

Note that this writes a single holding register.

UShort Data Values

HTTP Address Description
GET /ROArray/UShort/{offset} Reads an array of unsigned 16 bit integers from a Modbus slave.
GET /ROSingle/UShort/{offset} Reads an unsigned 16 bit integer from a Modbus slave.
GET /RWArray/UShort/{offset} Reads an array of unsigned 16 bit integer from a Modbus slave.
PUT /RWArray/UShort/{offset} Writes an array of unsigned 16 bit integer to a Modbus slave.
GET /RWSingle/UShort/{offset} Reads an unsigned 16 bit integer from a Modbus slave.
PUT /RWSingle/UShort/{offset} Writes an unsigned 16 bit integer (single holding register) to a Modbus slave.

Int32 Data Values

HTTP Address Description
GET /ROArray/Int32/{offset} Reads an array of 32 bit integers from a Modbus slave.
GET /ROSingle/Int32/{offset} Reads a 32 bit integer from a Modbus slave.
GET /RWArray/Int32/{offset} Reads an array of 32 bit integers from a Modbus slave.
PUT /RWArray/Int32/{offset} Writes an array of 32 bit integers to a Modbus slave.
GET /RWSingle/Int32/{offset} Reads a 32 bit integer from a Modbus slave.
PUT /RWSingle/Int32/{offset} Writes a 32 bit integer to a Modbus slave.

UInt32 Data Values

HTTP Address Description
GET /ROArray/UInt32/{offset} Reads an array of unsigned 32 bit integers from a Modbus slave.
GET /ROSingle/UInt32/{offset} Reads an unsigned 32 bit integer from a Modbus slave.
GET /RWArray/UInt32/{offset} Reads an array of unsigned 32 bit integers from a Modbus slave.
PUT /RWArray/UInt32/{offset} Writes an array of unsigned 32 bit integers to a Modbus slave.
GET /RWSingle/UInt32/{offset} Reads an unsigned 32 bit integer from a Modbus slave.
PUT /RWSingle/UInt32/{offset} Writes an unsigned 32 bit integer to a Modbus slave.

Float Data Values

HTTP Address Description
GET /ROArray/Float/{offset} Reads an array of 32 bit IEEE floating point numbers from a Modbus slave.
GET /ROSingle/Float/{offset} Reads a 32 bit IEEE floating point number from a Modbus slave.
GET /RWArray/Float/{offset} Reads an array of 32 bit IEEE floating point numbers from a Modbus slave.
PUT /RWArray/Float/{offset} Writes an array of 32 bit IEEE floating point numbers to a Modbus slave.
GET /RWSingle/Float/{offset} Reads a 32 bit IEEE floating point number from a Modbus slave.
PUT /RWSingle/Float/{offset} Writes a 32 bit IEEE floating point number to a Modbus slave.

Double Data Values

HTTP Address Description
GET /ROArray/Double/{offset} Reads an array of 64 bit IEEE floating point numbers from a Modbus slave.
GET /ROSingle/Double/{offset} Reads a 64 bit IEEE floating point number from a Modbus slave.
GET /RWArray/Double/{offset} Reads an array of 64 bit IEEE floating point numbers from a Modbus slave.
PUT /RWArray/Double/{offset} Writes an array of 64 bit IEEE floating point numbers to a Modbus slave.
GET /RWSingle/Double/{offset} Reads a 64 bit IEEE floating point number from a Modbus slave.
PUT /RWSingle/Double/{offset} Writes a 64 bit IEEE floating point number to a Modbus slave.

Long Data Values

HTTP Address Description
GET /ROArray/Long/{offset} Reads an array of 64 bit integers from a Modbus slave.
GET /ROSingle/Long/{offset} Reads a 64 bit integer from a Modbus slave.
GET /RWArray/Long/{offset} Reads an array of 64 bit integers from a Modbus slave.
PUT /RWArray/Long/{offset} Writes an array of 64 bit integers to a Modbus slave.
GET /RWSingle/Long/{offset} Reads a 64 bit integer from a Modbus slave.
PUT /RWSingle/Long/{offset} Writes a 64 bit integer to a Modbus slave.

ULong Data Values

HTTP Address Description
GET /ROArray/ULong/{offset} Reads an array of unsigned 64 bit integers from a Modbus slave.
GET /ROSingle/ULong/{offset} Reads an unsigned 64 bit integer from a Modbus slave.
GET /RWArray/ULong/{offset} Reads an array of unsigned 64 bit integers from a Modbus slave.
PUT /RWArray/ULong/{offset} Writes an array of unsigned 64 bit integers to a Modbus slave.
GET /RWSingle/ULong/{offset} Reads an unsigned 64 bit integer from a Modbus slave.
PUT /RWSingle/ULong/{offset} Writes an unsigned 64 bit integer to a Modbus slave.

String Data Values

HTTP Address Description
GET /ROSingle/String/{offset} Reads an ASCII string from a Modbus slave.
GET /RWSingle/String/{offset} Reads an ASCII string from a Modbus slave.
PUT /RWSingle/String/{offset} Writes an ASCII string to a Modbus slave.

HEX String Data Values

HTTP Address Description
GET /ROSingle/HexString/{offset} Reads an HEX string from a Modbus slave.
GET /RWSingle/HexString/{offset} Reads an HEX string from a Modbus slave.
PUT /RWSingle/HexString/{offset} Writes an HEX string to a Modbus slave.

Bits Data Values

HTTP Address Description
GET /ROSingle/Bits/{offset} Reads a 16-bit bit array value from a Modbus slave.
GET /RWSingle/Bits/{offset} Reads a 16-bit bit array value from a Modbus slave.
PUT /RWSingle/Bits/{offset} Writes a 16-bit bit array value to a Modbus slave.

Settings

HTTP Address Description
GET /Settings Reads the current settings (Modbus Master and Slave).
PUT /Settings Writes the current settings (Modbus Master and Slave).