Modbus

The Modbus Device Driver allows Iotellect Server to communicate with devices supporting Modbus Protocol. These devices may be connected to the system and, like with all other types of devices, their data is converted into a unified form, so they can be accessed from different Iotellect facilities. See Devices article for more information about the "normalized" representation of devices in Iotellect.

The Modbus driver supports both network versions (Modbus TCP and Modbus UDP) and serial versions (Modbus RTU, Modbus ASCII and Modbus BIN) of the protocol. Modbus serial devices should be connected to the COM ports of the PC running Iotellect Server.

If multiple Modbus devices reside on a serial bus (e.g. RS-485 bus), all devices will be connected to Iotellect through a single device account. Registers that belong to different devices should be added to a common Registers table (see below) with different Unit ID values.

There are two principal ways of connecting a serial Modbus device to Iotellect via an IP network:

In this case, the converter changes physical protocol (from Serial to Ethernet or Wi-Fi), but doesn't change application-level protocol. Therefore, Modbus ASCII or Modbus RTU data is transferred through an IP network "as is". On the server side, a Virtual Serial Port Driver is required to "catch" the IP traffic and expose it through a classic serial port. On the Iotellect Server side, a device account should be configured to work in Modbus Serial mode, communicating through the above virtual serial port.

Iotellect offers a wide range of Serial-over-IP converters (such as a DS1206 programmable controller running Serial-over-IP firmware), as well as Virtual Serial Port Driver for Windows and Linux operating systems.

Third-party converters paired by third-party virtual serial port drivers can be used for serial-over-IP conversion as well.

In this case, the converter changes both physical protocol (from Serial to Ethernet or Wi-Fi) and application-level protocol (Modbus ASCII or RTU to Modbus TCP). Thus, Modbus TCP data is transferred through an IP network. On the server side, Iotellect's Modbus Device Driver should be configured to work in Modbus TCP mode and directly connect to the device (or multiple devices on a bus) via an IP network.

Any of Tibbo's programmable controllers (such as a DS1206) that can run Modbus Converter application performing conversion physical and application protocol.

Third-party converters can be used for Modbus Serial to Modbus TCP conversion as well.

See Enabling Serial Communications if you have troubles connecting to Modbus Serial devices.

None defined.

None defined.

Connection settings define how Iotellect Server communicates with a certain Modbus device. These settings may be accessed using the Edit Device Properties action of Device Context. The following connection properties are available:

This property contains a list of Modbus device registers that are accessed and managed by Iotellect. Once a new Modbus device is added, one or more registers have to be configured to make device data available for the system. Each Modbus register is represented by a single variable of Device Context.

Modbus devices do not provide metadata, so Iotellect Server cannot learn about available Modbus registers of a particular device. That is why it's necessary to configure Device Registers manually.

Here is a list of properties of each Modbus register:

Property	Description
Name	Register name. This will be used as a Device Context variable used to access the register, so it may contain only letters, digits and underscore.
Description	Register textual description. Will be used as the description of the Device Context variable.
Type	Modbus register type. Possible values are Coil, Discrete Input, Input Register and Holding Register.
Format	Defines how to interpret value of one or more adjacent Input or Holding Registers. See type conversion section for details.
Register Address (decimal)	Address (offset) of the Modbus register in decimal form.
		This address is not an absolute address of a Modbus register. It indicates register offset from the beginning of the address space for registers of selected Type. For example, Address (offset) 1 for a register of a Holding Register type will match to: Protocol address 40000 Data model address 40001
Size	Number of registers to read by a single Modbus I/O operation and store in one Iotellect Server context variable. It may be useful to read multiple registers at once in the following cases: If they logically represent an array If they logically represent a string If they logically represent different parts of a complex data item that should be read in one atomic operation This setting has the default value of 1. The default should not be changed in most cases.
		The actual number of registers read in a single I/O operation will be N * M, where N is the number of registers required to hold one Iotellect Server-side value depending on Type and Format M is the value of Size parameter For example: if Type is Input Register, Format is 8-byte Float, and Size is 4, server will read 32 registers and represent them as a 4-element array (single-column Data Table) with Floating point numbers if Type is Holding Register, Format is Varchar, and Size is 64, server will read 64 registers and as a single-cell Data Table containing String value.
Unit ID	Modbus Unit ID. Identification (address) of a remote slave connected on a serial line or on other buses (e.g. RS485).

You can import the list of registers from a file (e.g. CSV file) by using Import function of Data Table Editor component.

If you wish to connect several similar Modbus devices to Iotellect, you could fill in the Device Registers table only once and then copy it to other devices using the Replicate action.

Assets are not supported by the driver.

Modbus device driver creates one Device setting variable per device register.

The following table shows how Modbus Registers are converted to Device context variables. Note that number of rows in each variable depends on the value of Size parameter. By default, all variables are single-row, i.e. scalar.

No operations provided by the driver.

No events provided by the driver.

This driver makes the device Online if:

• Serial port was opened successfully (for Modbus Serial devices)

• TCP connection with the device was successfully established (for Modbus TCP devices)

• Always (for Modbus UDP devices)

Synchronization between Iotellect Server and Modbus device includes the following steps:

• Creating a Settings Cache according to the Device Registers list. Each variable is used to access a single Modbus device register.

• Reading Modbus register values and storing these values in settings cache.

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