New Modbus TCP – DALI converter: Domat R090

After the Modbus TCP – DALI converter, M090, has been successfully sold for several years, a new version is being introduced – R090 with similar functionality, yet many improvements. They are described in the following text.

Multimaster functionality according to EN 60929 ed. 4:2011 Annex E, static priority 4

The M090 worked as a single master, i.e. there only could be a single device with the Application controller functionality, namely the M090. To understand the multimaster concept better, let us have a look at some system architecture examples, as described in IEC 62386-101:2014.

This norm primarily defines several device types on the DALI bus:

Bus power supply: Provides power to the other bus participants. In single master topologies it usually is the same product as the application controller, which is the case of the M090.

Application controller: A device which transmits two-byte control commands to the bus to control the Control gear. In the single master architecture, the Application controller needs not to detect collisions, as it is the sole device which sends commands to the bus. (The responses of other bus devices are reactions to these commands, and the Application controller knows that it may not transmit until these responses are received.)

Control gear: Maybe controlled gear would be a better naming, it is a ballast controller or another device which provides modulated power supply for the luminaire.

Input device: A device which transmits three-byte telegrams based on status or value change of inputs. It is a pushbutton, switch, movement or light intensity sensor or any other device which is used to control lighting. The input device telegrams are processed by Application controllers rather than by Control gears.  The Application controllers process the signals according to its internal program, and sends commands to the Control gears.

Example: user pushes the button (input device). The button does not send a command to activate light „light Y to ON“, but the information „button X pushed“. The Application controller receives this signal, and if there is a function that uses this information in its internal application program, the function is activated: e.g. if button X has been pushed, the command „light Y to ON“ is sent to the bus. The complete application is programmed in a single device, namely in the Application controller, and the Input devices and Control gears are only assigned their addresses. However, a pushbutton or switch may also contain the Application controller functionality, which will be shown later.

Now, the architectures as in IEC 62386-101:2014:

Single master architecture


There is only one Application controller on the bus (here combined with the Bus power supply) and several Control gears (ballasts with addresses 0…63). The Application controllr is the only bus participant that is allowed to start communication. If it is sending individual telegrams (such as ballast status queries) rather than group commands, the Control gears respond to the requests. This is the only possible architecture for the older converter M090, however, the R090 can be deployed in the Single master architecture, too.

The Single master architecture does not contain Input devices – switches, presence sensors, etc. The Input devices send spontaneous telegrams on status changes, and a Single master Application controller would not be able to detect collisions when trying to transmit concurrently with an Input device.

Multimaster architecture – with two or more Application controllers


This is the simplest Multimaster architecture, still with no Input devices. The Application controllers may be e.g. 3rd party interfaces (Domat R090), time scheduler controllers, dusk-to-dawn switches, etc. The two-byte commands to the Control gears can be sent by any  Application controllers at any time, and if there is a collision, all Application controllers are able to detect it and retransmit the message according to given priorities.

This topology is typical for control of luminaries in production halls, public spaces, etc. One of the Application controllers may be, for example, dedicated for diagnostics only – it queries the ballast statuses and sends alarms on broken lamps.

Multimaster architecture – with Input devices


In this architecture, Input devices can be found on the bus: buttons, switches, light sensors, etc. Any of the Input devices can send a three-byte signal on status change or periodically, and any of the Application controllers can send a two-byte signal to the Control gear(s). The Application controllers read information provided by the Input devices, process them according to their internal preprogrammed applications, and send the commands to the ballasts on the bus. If two Application controllers send concurrent commands, the last received command is valid.

Architecture with integrated Input devices


An integrated Input device combines funtions of Input device and Application controller in one box.  Typically, it is a programmable light sensor or programmable switch, which sends, apart from the three-byte signal „button X was pushed“ also a two-byte control signal to Control gear(s) – „set the light  Y to ON“, „activate scene Z“ etc. The control functionality must be programmed in the device. This is done using converters and software supplied by the device manufacturer. Simple devices may contain e.g. DIP switches to set the DALI Group or Scene number to be activated.

The R090 thus acts – regarding to EN 62386-101:2014  - as a multimaster application controller (however, without internal algorithm that could be bound to input device signals: all commands are accepted over the Modbus TCP interface or web page), combined with the Bus power supply. In other words, the R090 is not able to accept data from switches or other Input devices and process them, but it can share the bus together with another Application controller that does have this functionality.


The Priority number in DALI multimaster systems defines the importancy of commands the device issues. There are 5 priorities, numbered 0…4:

Priority 0: highest, temporarily assigned to commands that will be repeated
Priority 1: user actions where fast reaction on manual input is required (e.g. dim up with a special fade time)
Priority 2: configuration commands in general
Priority 3: automatic arc power control commands (such as by time scheduler or dusk-to-dawn switch)
Priority 4: lowest, ballast status queries (signalling of errors and broken lamps)

Most of the manufacturers do not mention priorities in their documentation. The R090 uses fixed priority 4 in the current firmware version.

Bus power supply

According to EN 62386-101:2014, one of the devices must provide a power supply to the DALI bus. The power supply may be only one on the bus, and its maximum current must not exceed 250 mA. The R090 is a bus power supply, which means that there may not be any other device with the bus power supply function on the bus. Using the single master topology, up to 64 control devices may be installed. A multimaster bus load shall not exceed the maximum total current for all devices (incl. input devices and application controllers) of 125 mA.

The R090 is powered either by 24 V AC, or over the network cable using the PoE (Power over Ethernet) standard. Power over Ethernet simplifies system design and enables deployment at projects where DALI lights are mounted into an existing installation, and a low-voltage cable can not be pulled. If the R090 is powered by 24 V AC and PoE at the same time, the device switches to 24 V AC.

New box with easy installation and better cooling

The R090 converter belongs to the new Domat I/O module and process stations family which is easy to see because of its  red Elbox housing. Improved mechanical construction protects the PCB better from intrusion of dirt and foreign objects, and provides more efficient cooling at the same time.

Same price as M090

Even when the hardware was redesigned and improved, and is ready for future functional extension, the price of R090 is the same as that of the M090. There is no impact on project under development, except the different box dimensions the R090 is fully backward compatible with the M090.