The main role of the DM-124 is to act as a IEEE 802.15.4 wireless bridge inside traditional wired RS485 Modbus RTU installations, providing the limited point-to-point RS485 networks with the versatility and ease of installation of wireless sensor networks (WSN).
The DM-124 is auto configurable, which means that each node automatically selects the best route to forward the data packets, effectively disseminating the Modbus commands to all connected devices.
Once installed, the DM-124 are transparent to devices inside the RS485 network, not only maintaining the electric requirements of the bus but also the integrity of Modbus RTU packet frames transmitted.
Its main features are:
- Wireless communication based on IEEE 802.15.4 (2.4 GHz)
- Auto configurable
- Modbus RTU wireless transmission
- 230 VAC power input
- Easy connection (Modbus A- and B+ terminals)
- Configurable pulse counter, with 3 operating modes: Dry-contact, Open-collector, S0 type (gas and water counters)
- Coordinator node - Modbus Bridge within ADVANTICSYS Wireless Sensor Networks
|Power supply||230 Vac|
|Protocols||Modbus RTU, Wireless IEEE 802.15.4|
|RS485 (1 port)||Up to 1.2 km range and 19.2 Kbits/s Baudrate (configurable)|
|Pulse counter (1 port)||3 operating modes: dry contact, open-collector or S0 type|
|Radio||2.4GHz - with External Antenna (SMA connector)|
|Case fixing type||DIN rail|
- Power Supply: The DM-124 must be powered directly from a 220Vac power source.
- Pulse input: The positive pole will be connected to Pulse+ terminal, and the negative to Pulse- terminal.
The DM-124 can be configured to receive different types of electrical pulses: open collector, open emitter and wet contact pulse (up to 30Vdc). For dry contacts, the configuration will be the same as the open collector.
- RS485 bus: The A line is connected to terminal A, and the B line to terminal B. If it is necessary to use the line termination of 120 Ω, the terminal T should be connected to terminal A with a wire. Additionally, if it is necessary to connect the GND of the RS485 line, it should be connected to terminal GND, which is beside the terminal T.
- Antenna: In the SMA connector of the DM-124 any antenna compatible with the 2.4GHz band could be connected.
Pulse input configuration
Important: Pulse counter functionality is available for devices with serial number 65300 onwards.
By default, the DM-124 is configured for wet contact pulses, so, if it is necessary to change the type of pulse input, the DM-124 can be opened as shown below:
Internally, the DM-124 has a pin block (JP1) which configures the type of pulse input depending on the jumper connection. There are three electrical pulses that can be connected to DM-124:
- Open collector. The jumper should be connected on position 1 of block JP1. This configuration is also valid for dry contact pulses.
- Open emitter. The jumper must be positioned in pos 3.
- Wet contact pulse. In this case, the jumper will be connected on position 2.
How to read/write DM-124 Modbus registers
Due to the wireless physical layer, the maximum number of registers that could be read in one request is 16, and the maximum number registers that could be written in one order is also 16. Also, as we already described, the minimum interval between Modbus orders should be at least one second, even for writing orders should be upper. The Modbus timeouts must be complaint with this timing to avoid the collapsing of the wireless communications. The user can change the timing and retries of the radio ACKs to accelerate the communications, but it will be under his/her responsibility. The DM-124 itself has accessible some MODBUS registers for its own configuration and the pulse counter. In the following chapters, specific Modbus registers will be shown.
As we see in previous chapters, the DM-108 configuration can be performed through the use of our WM Config Tool. However, it is also possible to read/write directly on the corresponding registers.
Of them, the most important registers are:
- Register 4224:
- High byte. Represents the Group ID. It has a range between 0 and 255.
- Low byte. Radio channel, range between 11 and 26.
- Register 4226:
- High byte. It has Modbus ID and its range is between 1 and 247. 0 and 255 are forbidden.
- Low byte. Number of slave motes, in case Advanticsys slave motes are used in the network
- Register 4228:
- High byte. Number of slave registers
- Low byte. RS485 port configuration:
Using the DM-124 as pulse counter
As explained before, the pulse counter can be configured by setting the jumper in the adequate position. To read the stored pulse counter value register address 4096 must be read, with a size of 2 (uint32).
Using the DM-124 to map slave devices
It is possible to map additional wireless sensors (such as those provided by advanticsys) as DM-124 slave nodes. To do so it is necessary that the slave node sends messages in a predefined format, so that the DM-124 can recognize it as a potential slave node. Moreover, the specific slave node has to be mapped in the DM-124 as a valid slave to enable the data acquisition.
Theory of Operation
The following diagram shows the interconnection of different Modbus RTU compatible equipments through a wireless network created with the DM-124:
The Modbus master device, which can be a PLC, a PC or an Advanticsys controller, interrogates the Modbus devices within the network. The RS485 serial packets are converted to wireless packet frames by the connected DM-124 (id 10 in the picture) and broadcasted to the rest of the DM-124 in the network. These convert them in turn to RS485 Modbus RTU, forwarding them to the connected Modbus devices. Replies from the devices are transmitted in the same way to the network coordinator.
Since the DM-124 are considered also as Modbus devices within the network, data from the included pulse counter can be read by retrieving the data from the registers of the specific DM-124. This pulse counter is configurable as dry contact, open-collector or S0 type (for water and gas counters).
Configuration of the DM-124 can be done with a dedicated programmer and also through the Modbus network. Among other parameters it is possible to configure:
- The Modbus identifier and their master or slave behaviour
- The IEEE 802.15.4 radio channel, and the radio cluster identifier, allowing different networks to coexist
In order to extend the network and/or the number of devices, groups of DM-124 can be connected in cascade as the following diagram shows: