The functionality of the DOMIQ/Base in software version 1.7.5 has been updated with support of the MODBUS/TCP and MODBUS/UDP protocols. The Base module plays the role of the master device. It enables integration with many commonly used automation devices like PLCs or usage of the protocol converters from MODBUS/TCP to MODBUS RTU using a standard Ethernet network.
In this tutorial you can find:
- basic information about the MODBUS/TCP protocol
- configuration description of the Base module in order to integrate it using MODBUS/
- TCP
- integration description of the Base module with a modular Beckhoff PLC.
1. MODBUS/TCP Protocol #
MODBUS/TCP is a modification of a standard MODBUS RTU protocol, in which the transport layer based on RS-485 was replaced by the TCP/IP protocol. Some devices use a non-standard variant, in which the connectionless UDP protocol was used instead of TCP.
TCP and IP protocols play only the transport role – they enable the exchange of data between devices. The exchanged data are interpreted exactly the same, as in the case of MODBUS RTU, including the requirement of a single response after each query. The main task of the TCP protocol is to monitor that all data packets are transmitted correctly between devices in the order of sending, while the IP protocol (Internet Protocol) is responsible for sending the data to the recipients through many indirect devices-routers. The encapsulation of the MODBUS packet was shown in the below scheme:
MODBUS/TCP and MODBUS/UDP packets are sent to the port 502, which is reserved for this purpose.
MODBUS/TCP has several features which surpass the MODBUS communication using the serial port:
- easy connection of many controllers; any distance
- faster data transmission
- using the already existing network structure (routers, switches, wiring etc.)
- reliability of the data transmission thanks to correctness control mechanisms in the TCP protocol and automatic repetitions in case of errors or lost packets. This function is not available in the UDP variant.
2. Configuration of the Base module #
In this chapter we present how to prepare the Base module for the communication using MODBUS/TCP.
- Choose the MODBUS tab.
- Add a new interface and click on it in order to fill in its properties.
- Enter the name (without spaces). The name of the interface is used while creating the names of identifiers (see below).
- Set TCP as Type.
- In the IP Address field enter the IP address of the slave device.
- The Port field is filled in by default with the value of 502. However there are devices which use another TCP port. In such case enter the port number in this field.
- Add a new device:
- Enter the name (without spaces). The name of the device is used while creating the names of identifiers (see below).
- In the Description field you can add any description of the device
- In the Address field enter the address of the slave device.
- Add the registers that you want to read/save and then set their parameters: type, address and name.
If the devices are connected and set correctly, then the value of the read/saved registers are displayed in the State tab.
The identifiers have the following syntax:
MODBUS.<inerface>.<device>.<register>, np. MODBUS.bk.dev.temp.
The values of the MODBUS registers can be displayed on the visualizations or Remote application and connected with events, timers etc.
The example configuration used in the integration of the Base module with the Beckhoff controller was presented in the picture below:
3. Integration with the modular Beckhoff controllers #
MODBUS/TCP protocol enables integration of the DOMIQ system with any device which supports this protocol. One of the available options is the integration of the DOMIQ system with the modular Beckhoff controllers.
Beckhoff offers a wide range of devices which are commonly used in automation installations, on the basis of which you can create an intelligent installation:
- dimmers (e.g. KL2751);
- relays (e.g. KL2641 lub KM2604);
- modules to control the engines (e.g. KL2552 lub KL2791) – to control recuperation;
- digital outputs (e.g. KL2408) and analog outputs (e.g. KL4408);
- digital input modules (e.g. KL1408) and analog input modules (e.g. KL3408);
- sensors (temperature, humidity, pressure);
- devices monitoring the energy network;
- and many other.
A device which controls the inputs and outputs directly can be a network coupler which also plays the role of MODBUS/TCP interface, e.g. Beckhoff BK9050 or one of the available PLCs, e.g. BC9050. It is recommended to use the PLC when there is the need of creating logical relationships or faster reaction times than it is possible using the Base module.
An important feature of the Beckhoff controllers is the fact, that they can be easily extended. You can connect 64 extension modules by default or 255 if the bus is extended. The example configuration of the controller is shown on the next page.
Extension modules can be exchanged for other ones anytime, without the need to reconfigure the controller.
The Base module has function of the master device in relation to the Beckhoff controllers. It means, that when you integrate the DOMIQ system with the Beckhoff controller, you can use all its functionalities. The data from the Beckhoff controller can be visualized or used in events, timers, lua scripts etc. The outputs can be freely controlled from the DOMIQ user interface.
3.1. Additional configuration remarks #
During the configuration of the Beckhoff controller, in addition to the way of initialization of the IP address, it is also necessary to set the periodic reset of the register No. 4384 – communication watchdog. When the controller receives the first message, restart the register with a set frequency, max. every second. Otherwise the controller stops the communication itself.
The periodic reset can be performed as follows:
- Add the read-out from the register No. 4384 in the MODBUS tab. Set the type uint16 and enter wd.
- Add an event:
- In the Channel field enter: E.MODBUS.<interface>.<device>.<register> e.g. .MODBUS.bk.dev.wd.
- In the field Data enter: 1000.
- Add a command:
- In the field Name enter: E.MODBUS.<interface>.<device>.<register> in this case .MODBUS.bk.dev.wd.
- In the field Value enter: 1000.
4. Reading the inputs and controlling the outputs #
The implementation of the MODBUS protocol in the Base module allows you not only to read the registers (all available types) and inputs, but also save the values in the registers (only uint16 and int16) and control the outputs (coil). The registers, inputs and outputs are read after adding them in the MODBUS tab and filling in its parameters (type, name, address).
In the Beckhoff controllers the extension modules are counted from the left and the numbers of the inputs and outputs are given in this order. If you connect two modules of the digital outputs, e.g. KL2408, then the outputs of the first module have the numbers from 1 to 8 and the second from 9 to 16 etc.
The registers from 0x0000 to 0x00FF are assigned to the inputs and 0x0800 to 0x08FF to the outputs. For example, if there are eight digital inputs connected to the BK9050 module, e.g. KL1408, the input states are stored in the registers from 0 to 7.
There are standard commands which are used to save the values of the registers/outputs. In order to save the value in the register just send the following command: C.MODBUS.<interface>.<device>.<register>=value e.g. C.MODBUS.dev.bk.temp=25.
The output values are saved similarly. The difference is that the output accepts one of four commands: on, off, 1 or 0. For example: C.MODBUS.dev.bk.light=on or C.MODBUS.dev.bk.light=0.
It is also possible to control MODBUS/TCP from the Display visualization or Remote menu using channel elements. In such case use the following channel identifiers: MODBUS.<interface>.<device>.<register>, e.g. MODBUS.dev.bk.light
Using the described functionality you can create the building automation installation based on the DOMIQ modules and a single Beckhoff controller or use it to complete the installation functionalities based on the LCN system.
