EM-482 i EM-482-1 to konwertery protokołów produkowane przez NOVATEK-ELECTRO LTD. Zapewniają komunikację MODBUS między klientami i serwerami w sieciach TCP oraz między urządzeniami z interfejsem RS-485 przez Wi-Fi.
Mount your EM-482 on a standard 35mm DIN rail in a well-ventilated location. The device operates from -35°C to +45°C, but avoid areas with excessive vibration, humidity, or corrosive atmospheres.
Before making any electrical connections, ensure all devices are powered off.
Tighten terminal screws to 0.4 N·m — enough for solid contact without damage.
Antenna connection: If it is EM-482-1 model, place the antenna in reach of the Wi-Fi access point (e.g. outside the metal case where the device is mounted). Connect the antenna cable to the ANT connector of the EM-482-1, then tighten it.
RS-485 wiring: Connect twisted-pair cable to EM-482’s RS-485 terminals: terminal A for non-inverted signal, terminal B for inverted signal (your devices might label these as A/D+/+ and B/D-/- respectively). Run the cable to your Modbus devices and connect accordingly. Use shielded twisted-pair cable (Category 1 or better) for reliable communication over distance.
Power: Connect 12V DC power to the 7÷30V terminals. For safety, install a 0.5A fuse in the power circuit. Use stranded wire with ferrules, stripped 5mm. Wire cross-section should be 0.5-3 mm².
When you apply power, all LEDs light up briefly during the 2-second initialization, then the device spends 10-30 seconds establishing Wi-Fi connection.
The PWR LED stays green to confirm power. The WI-FI LED blinks rarely (every 3 seconds) when establishing the connection and turns on when Wi-Fi connects (blinking afterwards during data transfers).
The WI-FI and SRV indicators flashing alternately indicate that the Wi-Fi setup mode (access point) is enabled.
Connect to EM-482 access point: Open your device Wi-Fi list and select the «EM482_xxxxxx» network (where xxxxxx are the last 6 characters of the Product’s MAC address indicated on the product label).
Open EM-482 web interface: Open your browser and enter the http://em.com or http://192.168.4.1 address.
Configure Wi-Fi network: Select the EM-482 future access point, enter its password, enable/disable DHCP, set static IP if needed, adjust subnet mask and gateway.
Configure Modbus RTU/ASCII: This can be done at the cloud server later. Consult the manual of your Modbus devices for their parameters (baud rate, parity and stop bits settings), then match these exactly in EM-482. If no manual is available, start with common values: 9600 or 19200 baud, Modbus RTU protocol, and AUTO-STOP parity (which automatically detects the correct stop bits setting).
Check additional parameters: Set the remote Modbus TCP server connection, configure cloud server address, set the password, select product hostname to distinguish it in the router lists.
Overvis Cloud provides remote monitoring and control through a web dashboard. The device label includes a QR code and PIN for quick setup.
Access Overvis server: Scan the QR code on the device label or manually enter the link from the label (format: https://c.overvis.com/ABCD1234 where the last part is your PIN). The link redirects to Overvis server’s login page. Optionally follow the Overvis link on the Cloud tab.
Login or create account: Enter your credentials if you have an account. New users should create an account first.
Create Network: After login, Overvis shows the “Create Network” page. If you came from the QR code/link, the PIN is pre-filled. Otherwise, enter the PIN from the device label and click “Check connection.”
Verify connection status: Overvis displays the connection status — either “Connected” or “Device is not connected to the server.” If not connected, check that EM-482 has Internet access. The SRV LED should turn on shortly after the WI-FI LED.
Configure your network: Give your network a descriptive name (a “network” represents your EM-482 plus all connected Modbus devices). EM-482 itself (unit ID 111) is added automatically.
Add connected devices: Select your RS-485 device models from the dropdown menus and enter their Modbus addresses. Overvis creates device instances from templates matching your selections.
Test communication: Open a device page in Overvis and read its parameters to confirm real-time communication is working.
Troubleshooting cloud connection:
Device is not connected at the server → Check Internet connectivity, review Cloud address in web interface settings
PIN not accepted at the server → Verify you entered the exact PIN from this device label
Can’t create account → Ensure email address entered is valid, check email for verification link
The PWR indicator is constantly red or blinking fast in red: This may be due to device malfunction. Contact the seller or manufacturer of the product.
The WI-FI indicator does not remain on, but is blinking rarely (every 3 seconds, for more than 2 minutes): The Wi-Fi access point is unavailable. Normal during first 30 seconds while the connection is established. If it persists, check the Wi-Fi settings, access point distance and that it is powered.
The SRV indicator remains off (for more than 2 minutes): EM-482 is not connected to the Internet. Verify the server connection address in the web interface. Your network firewall may be blocking outgoing connections. If the issue persists, check the router Internet access.
The WI-FI and SRV indicators keep blinking alternately: The EM-482 is in setup mode. Either complete the configuration, or exit the mode by pressing the R button on the front panel for about 3 seconds.
Cannot access EM-482 web interface: Check the EM-482 is in setup access point mode (the LEDs are blinking alternately). Check your device is connected to EM-482 access point. Use http://em.com or http://192.168.4.1 address to access the web interface.
Device already registered error at server: The device is bound to another Overvis account. Use the Unbind button (if it is in one of your accounts), or contact the server administration (or the previous owner) to remove the device from their account.
Intermittent connection drops: Check that the power supply voltage is within the required range (7-30V DC) and can provide sufficient current (up to 110mA). Look for electrical noise or interference sources near the device. Update EM-482 firmware to the latest version.
RS-485 devices not responding: Verify the RS-485 wiring is correct (A and B terminals). Check that the RS-485 bus termination is properly configured. Verify Modbus RTU/ASCII settings match the connected devices. See the Modbus Interface documentation for detailed communication settings.
This Operating Manual explains the design, safety requirements, operating rules, and maintenance procedures for the EM-482 and EM-482-1 Protocol Converters (hereinafter referred to as “Protocol Converter”, “Product”, or “EM-482”; the name “EM-482-1” is used when the characteristics differ).
Figure 1 – Overall and mounting dimensions and controls
The + and - terminals are designed for power supply connection (from 7 to 30 VDC).
Terminals A, ⊥ and B are used for connecting to the RS-485 network connection.
Terminals are not used.
SMA-F ANT connector (only for EM-482-1) is used for connecting a Wi-Fi antenna (included).
The WI-FI indicator is lit while Wi-Fi is connected, blinks every three seconds when searching for a Wi-Fi network, and blinks alternately with the «SRV» indicator in the Wi-Fi setup mode.
The 485 indicator lights up when waiting for transmission over RS-485 and blinks when data are being exchanged over RS-485.
The SRV indicator lit while the data collection server is connected, blinks when data is being exchanged with the server, and blinks alternately with the «WI-FI» indicator in the Wi-Fi setup mode.
The PWR indicator is green during normal operation and flashes red when a communication error occurs.
Reset Button R may be used for: entering the Wi-Fi setup mode; restarting the Product; and resetting the parameters to the manufacturer’s defaults.
If the temperature of EM-482 after transportation or storage differs from the ambient operating temperature, keep EM-482 under operating conditions for at least two hours before connecting it to the power supply. This prevents condensation on internal components.
To ensure reliable electrical connections, use flexible (stranded) wires. Strip the insulation from the wire ends by 5±0.5 mm and crimp with suitable ferrules. It is recommended to use wire with a cross-section of at least 1 mm².
When connecting to the RS-485 bus, use twisted-pair cable of category 1 or higher. A shielded cable is recommended; in that case, ground the shield according to “ANSI/TIA/EIA-485-A-1998”.
Route and fasten wires so as to avoid mechanical damage, twisting, or abrasion of the insulation.
For a reliable contact, tighten the terminal screws with the force indicated in Technical specifications.
To improve safety and reliability, it is recommended to install the fuse F1 (or its equivalent) in the EM-482 supply circuit, rated for a current of no more than 0.5 A.
After power is turned on, all indicators light up, and EM-482 performs initialization.
After approximately 2 seconds, the indicators (except for the PWR indicator, which turns green) go out, and the Product proceeds to start the Wi-Fi network interface.
Startup can take up to 30 seconds.
If the WI-FI indicator lights up, the connection to the network was successful.
The WI-FI indicator blinking every three seconds indicates the process of connecting to the network.
The WI-FI and SRV indicators flashing alternately indicate that the Wi-Fi setup mode (access point) is enabled.
After this, if enabled in settings, EM-482 establishes a connection with the cloud server.
By default, cloud connection is enabled.
If configured, EM-482 establishes TCP connections and waits for incoming TCP connections.
The EM-482 is a protocol converter that bridges RS-485 Modbus RTU/ASCII networks with Modbus TCP networks. It operates in multiple communication modes simultaneously, providing flexible connectivity through Wi-Fi networks, and RS-485 interface. Each mode serves a distinct purpose and can be used independently or in combination to meet your application requirements.
EM-482 can establish and maintain a persistent outbound connection to a cloud server (using Modbus TCP protocol).
EM-482 initiates the outbound connection to the server, bypassing firewall issues
After connection is established, EM-482 sends its MAC address for identification as a first Modbus TCP packet (response for function 3)
After that it operates in slave mode, waiting for and processing server requests
The server sends Modbus requests through this connection
EM-482 forwards these requests to RS-485 devices or responds with its own register values
Returns responses back to the server
If the SRV LED is on, the connection to the server or VPN has been successfully established
If the SRV LED blinks, data is being exchanged via this connection
Use case: Centralized monitoring and control of distributed equipment through cloud platforms like Overvis Cloud, enabling remote access from anywhere without configuring firewall port forwarding or static IP addresses.
Pair two EM-482 units to extend RS-485 networks beyond physical distance limitations by converting to/from TCP.
One EM-482 operates in master mode on its RS-485 interface, while the other is in slave mode
First EM-482 receives RS-485 signals and converts them to TCP packets
Data is transmitted over any distance via TCP/IP networks
Second EM-482 receives TCP packets and converts them back to RS-485 signals
Creates a transparent Modbus bridge between two RS-485 networks or segments
Each EM-482 can operate in master or slave mode on its RS-485 interface as needed
Use case: Connecting RS-485 networks in separate buildings without running long cable runs, extending RS-485 beyond the 1200m distance limit, or accessing remote sites via Internet.
EM-482 configuration can be performed in two ways:
via the web interface, using a browser to configure the most important parameters in the Wi-Fi setup mode (see Quick Start Guide);
via the Modbus protocol, using cloud server or any Modbus client software that works with EM-482’s own registers (see Modbus interface).
Use the service R button on the front panel to get into Wi-Fi setup mode, restart the controller, or reset factory settings.
To reset the device to factory settings:
Press and hold the R button for at least 8 seconds. After 2 seconds, the PWR indicator will light up red. After 8 seconds, the settings are reset, and the device restarts; all the indicators blink once.
Release the R button.
To switch Wi-Fi setup mode on or off:
Press and hold the R button for 2 to 8 seconds.
When the PWR indicator lights up red, release the R button.
All the indicators blink once, and the device restarts.
To reset the device (while preserving the settings):
Briefly press and release the R button.
All the indicators blink once, and the device restarts.
You may transport and store EM-482 in the original package at temperatures from minus 45 to +60 °C and relative humidity of no more than 80%. When transporting EM-482, protect it against mechanical damage.
The EM-482 uses standard TCP/IPv4 addressing for Wi-Fi communication. DHCP is enabled by default, allowing the device to automatically obtain network settings from your router. Without DHCP the factory default IP address is 192.168.0.111.
IP Addressing Fundamentals
When devices communicate over a network using the TCP/IPv4 protocol, each device uses IP addressing settings to identify the sender and receiver of data. EM-482 stores the following in its memory:
IP Address: A unique address within the subnet (four bytes written as integers 0-255, separated by dots)
Subnet Mask: Identical for all devices within the subnet (written similar to IP address)
Gateway Address: Used to communicate with other networks
Requirements for Proper Communication:
Devices within a subnet communicate properly when these conditions are met:
Common Subnet Mask: All devices in the subnet must use the same mask. Most small LANs use 255.255.255.0.
Valid Mask Format: The mask starts with consecutive 1 bits, followed by consecutive 0 bits.
Subnet Address: All IP address bits corresponding to the mask’s 1 bits must be identical across all devices. Common LANs use 192.168 as the address prefix with mask 255.255.255.0. The third byte can serve as a subnet number in complex LANs; in smaller LANs, it’s typically 0.
Unique Host Address: The IP address bits corresponding to the mask’s 0 bits must be unique to each device within the subnet.
Gateway Configuration: A router or gateway device that communicates with other networks typically uses an address like 192.168.0.1, 192.168.0.100, or 192.168.0.101. Other devices can use this address as their gateway. The gateway address is not required for intra-subnet communication—only for connecting to external networks (such as the Internet).
EM-482 supports three connection methods via Wi-Fi.
Method 1: Wi-Fi setup access point mode
This mode is only used to configure EM-482 essential communication parameters. It is not intended for Modbus communication.
Press the R button on the front panel for about 3 seconds.
After the button is released, on entering this mode the WI-FI and SRV LEDs would start blinking.
The Wi-Fi access point EM482_XXXXXX would become available, where XXXXXX are the last symbols of the device MAC address (shown on its label).
Connect to this access point with your device, open the browser and enter em.com (or 192.168.4.1) in its address line.
Select the Wi-Fi access point for EM-482 to connect to.
Save settings then restart the device.
Method 2: Network with DHCP Server
If your network access point has DHCP server that assigns IP addresses to new devices:
Enter EM-482 configuration mode (see method 1)
Select Wi-Fi access point for EM-482 to connect to
Enable DHCP server addressing
Save settings and reboot EM-482
EM-482 would connect to the cloud server, and can be managed there (if the access point provides Internet access)
To access EM-482 locally, check its local IP address in the access point router DHCP table, or fix the EM-482 address as static in the access point router settings
Method 3: Network Without DHCP
If DHCP is unavailable, or a static address should be used outside the DHCP range:
Enter EM-482 configuration mode (see method 1)
Select Wi-Fi access point for EM-482 to connect to
Disable DHCP server addressing
Set the static IP address, mask and gateway address according to your access point network setup. The EM-482 address should be unique in the network. The gateway is needed only for Internet access (cloud server and firmware updates)
Save settings and reboot EM-482
EM-482 may connect to the cloud server, and can be managed there (if the manual IP settings are correct and the gateway provides Internet access)
To access EM-482 locally, use its manually configured address
Connect EM-482 to a router using one of the methods above
Ensure the router is connected to your Internet service provider (ISP)
This setup enables outgoing connections (e.g., active-mode connection to cloud servers, connections to other servers using their static IP addresses).
graph LR
A[EM-482] -->|Wi-Fi| B[Router]
B -->|WAN| C[Internet/ISP]
B -->|LAN| D[Local Network]
C --> E[Cloud Server / Remote Modbus TCP Devices]
D --> F[Modbus TCP Devices]
Fig. 3 – EM-482 Internet connection topology via Wi-Fi with DHCP
To access the device from the Internet via incoming connections (direct TCP connection or web interface):
Acquire a Static IP: Get a dedicated line with a static IP address from your ISP
Connect the ISP cable to the router’s uplink port (usually color-coded, see router documentation)
Connect EM-482 to the router
Configure Router: Following your ISP’s recommendations, configure the router for Internet access using the router documentation.
Set Up Port Forwarding: Configure the router to redirect queries from your static public IP address to EM-482’s local IP address. For Modbus TCP access: redirect to the incoming connections port (register 450, factory default: 502). See Modbus Interface for register configuration details.
graph LR
A[Internet Client] -->|Public IP:Port| B[Router]
B -->|Port Forward| C[EM-482]
C -->|RS-485| D[Modbus Devices]
Fig. 4 – EM-482 incoming connections via port forwarding
Configure DHCP Reservation: Either:
Configure the router to always assign the same IP address to EM-482 via DHCP, OR
Disable DHCP in EM-482 settings and use a static IP
This ensures port forwarding works correctly.
Verify Security: Confirm that EM-482’s Internet connection is protected by standard security measures (see Connection Security). Specifically set the setup password and write access password to some unique values. It is also recommended to set the read access password.
Access the Device: When accessing EM-482 from the Internet, use the static IP address provided by your ISP and the public port specified in your port forwarding configuration
EM-482 has basic protection against unauthorized access via network. Access for writing and/or reading via Modbus can be deactivated in settings.
Device settings can be changed remotely by entering a password (minimum 5 characters). Access passwords can be set for restriction of writing and/or reading via Modbus.
When entering the password, all settings are only available to the specific client. In case of no requests from the client over a long period, the access returns to locked mode.
EM-482 supports constant communication with data collection and management servers, for example, Overvis Cloud.
EM-482 factory settings are preconfigured for Overvis connection, once the Internet access is provided, EM-482 would connect to the cloud server. The Overvis system uses MAC address-based authentication — the device’s unique MAC address is sent to the server at each connection session.
There are two ways to connect EM-482 to Overvis Cloud:
Using PIN/QR Code from Label (Recommended for first-time setup) — The fastest method using reverse connection where EM-482 connects to Overvis. Simply scan the QR code on your device label. Detailed in Quick Start Guide.
Direct Connection from Overvis (For advanced users) — Overvis connects directly to EM-482 through router port forwarding, requiring a static public IP address. Used rarely due to complexity and security considerations.
This is the recommended method for first-time setup, using the registration information from your EM-482 label.
sequenceDiagram
participant EM-482
participant Overvis
participant User
EM-482->>Overvis: Connect & send handshake (MAC address)
Overvis->>EM-482: Confirm handshake
Note over EM-482,Overvis: Connection established, waiting for binding
User->>Overvis: Scan QR code / Enter PIN URL
User->>Overvis: Login to account
User->>Overvis: Submit PIN in "Create Network" page
Overvis->>Overvis: Link PIN to MAC address
Overvis->>Overvis: Find matching connection by MAC
Overvis->>User: Create network under user's account
loop Data Communication
User->>Overvis: Request device data
Overvis->>EM-482: Read registers (via established connection)
EM-482->>Overvis: Return data
Overvis->>User: Display data
end
Connection Flow: EM-482 initiates outbound connection to Overvis and maintains it. User registers by linking the PIN to this existing connection. No port forwarding required.
Prerequisites:
EM-482 connected to Internet
QR code label on device (or PIN code from label)
Overvis Cloud account (or create during setup)
Connection Steps:
Verify Internet Connection
Ensure EM-482 is connected to the Internet. Check the Wi-Fi and SRV LEDs are both on.
Access Overvis Server
Scan the QR code on the device label with your phone or tablet, OR manually enter the URL from the label (format: https://c.overvis.com/ABCD1234). The link automatically redirects to Overvis server login page with the PIN embedded in the URL.
Login or Create Account
If you have an account, enter your credentials. New users should register for a free account first.
Create Network
After login, Overvis displays the “Create Network” page. If you came from the QR code/link, the PIN is pre-filled automatically. Otherwise, manually enter the PIN from the device label. Click “Check connection” to verify EM-482 is online.
Configure Network
Give your network a descriptive name (a “network” represents your EM-482 plus all connected Modbus devices). EM-482 itself (Modbus unit ID 111) is added automatically. Add your RS-485 devices by selecting models and entering their Modbus addresses.
Verify Operation
Open a device page in Overvis and read parameters to confirm real-time communication.
This method allows Overvis to connect directly to your EM-482 using its public IP address. It requires more advanced network configuration.
sequenceDiagram
participant User
participant EM-482
participant Router
participant Overvis
User->>Router: Configure port forwarding<br/>(Public IP:Port → EM-482:502)
User->>EM-482: Set static/reserved IP
User->>Overvis: Add network with direct connection method
User->>Overvis: Enter public IP & port
Overvis->>Router: Connect to Public IP:Port
Router->>EM-482: Forward to EM-482:502
EM-482->>Router: Modbus TCP response
Router->>Overvis: Forward response
Overvis->>User: Show device online
loop Data Communication
User->>Overvis: Request device data
Overvis->>Router: Read registers request
Router->>EM-482: Forward request to EM-482:502
EM-482->>Router: Return data
Router->>Overvis: Forward response
Overvis->>User: Display data
end
Fig. 11 – Connection sequence for direct connection method (incoming connection)
Connection Flow: Overvis initiates inbound connection to EM-482 through router port forwarding. Requires static public IP.
Prerequisites:
Static public IP address from your ISP
Router with port forwarding capability
EM-482 connected to your LAN
Overvis Cloud account
Basic understanding of router configuration and network security
Connection Steps:
Obtain Static Public IP
Contact your Internet Service Provider to obtain a static public IP address for your location. Dynamic IP addresses are not recommended as they may change. Some ISPs offer static IP as a paid add-on service.
Configure Router Port Forwarding
Access your router’s configuration interface and set up port forwarding to redirect external connections to EM-482. Forward to EM-482’s Modbus TCP port (default: 502). External port can be the same (502) or different for security. Forward to EM-482’s internal IP address (e.g., 192.168.0.111).
graph LR
A[Overvis Cloud] -->|Public IP:Port| B[Router]
B -->|Port Forward to 192.168.0.111:502| C[EM-482]
C -->|RS-485| D[Modbus Devices]
Fig. 12 – Direct connection port forwarding configuration
Configure DHCP Reservation or Static IP
Ensure EM-482 always has the same internal IP address:
Option A: Configure your router to assign EM-482 a reserved IP via DHCP (recommended)
Option B: Disable DHCP on EM-482 and manually configure a static IP address in the web interface
Verify EM-482 Accessibility
Test the connection from outside your network. Use a Modbus TCP client from a different network (e.g., mobile hotspot), connect to your public IP address on the forwarded port, and try reading a register from EM-482 (unit ID 111, register 1 for firmware version).
Configure Security (Strongly Recommended)
Set the strong Modbus TCP password in EM-482 settings. Consider changing the external port to a non-standard number. Configure your router’s firewall to restrict access by IP range if possible. See Connection Security for additional recommendations.
Create Network in Overvis
Log in to your Overvis Cloud account at www.overvis.com. On the “Create Network” page, select the direct connection method. Enter your static public IP address and the external port number (as configured in router). Enter EM-482’s Modbus address (default: 111) and Modbus password if configured.
Configure Network
Give your network a descriptive name (a “network” represents your EM-482 plus all connected Modbus devices). EM-482 itself (Modbus unit ID 111) is added automatically. Add your RS-485 devices by selecting models and entering their Modbus addresses.
Verify Operation
Open a device page in Overvis and read parameters to confirm real-time communication. Monitor connection stability over 24-48 hours.
The only method of connection EM-482 to other cloud servers and SCADA systems is the direct connection method via Modbus TCP.
Configure EM-482 in the monitoring system as a remote Modbus TCP device. This requires setting up port forwarding on your router to redirect external connections to EM-482’s local IP address and Modbus TCP port (default: 502). Your server will initiate connections to EM-482 through your router, similar to Method 2 described above. You’ll need a static public IP address from your ISP.
Since EM-482 uses the standard Modbus TCP protocol for direct connections, no special server software is required—any Modbus TCP client can communicate with the device. See the Modbus Interface documentation for complete register mappings and communication protocols.
Problem: EM-482 WI-FI LED does not remain on, but is blinking rarely (every 3 seconds, for more than 2 minutes).
EM-482 is not connected to your Wi-Fi access point. Either Wi-Fi access point is misconfigured, or the access point is unavailable. If the issue persists, verify the Wi-Fi access point is properly configured in EM-482 settings.
Problem: EM-482 SRV LED remains off (for more than 2 minutes).
EM-482 is not connected to the Internet. Verify the server connection is enabled in the web interface. Check that the server address and port are correct in settings. Your network firewall may be blocking outgoing connections. If the issue persists, check the router internet access.
Problem: EM-482 WI-FI and SRV LEDs keep blinking alternately.
The EM-482 is in setup access point mode. Either complete the configuration, or exit the mode by pressing the R button on the front panel for about 3 seconds.
Problem: Cannot access EM-482 web interface
Check the EM-482 is in setup access point mode (the LEDs are blinking alternately). Check your device is connected to EM-482 access point. Use em.com or 192.168.4.1 address to access the web interface.
Problem: “Device already registered” error
The device is bound to another Overvis account. Use the Restart Activation button in the Cloud settings page to unbind it, or contact the server administration (or the previous owner) to remove the device from their account.
Problem: Intermittent connection drops
Check that the power supply voltage is within the required range (7-30V DC) and can provide sufficient current (up to 110mA). Look for electrical noise or interference sources near the device. Update EM-482 firmware to the latest version.
Problem: RS-485 devices not responding
Verify the RS-485 wiring is correct (A and B terminals). Check that the RS-485 bus termination is properly configured. Verify Modbus RTU/ASCII settings match the connected devices. See the Modbus Interface documentation for detailed communication settings.
Community: Check the user forums for solutions from other EM-482 users
For warranty service or hardware issues, please contact your authorized distributor or the manufacturer directly.
Novatek-Electro EM-482 Documentation
Modbus Interface Reference
The EM-482 operates as a Modbus gateway, listening for Modbus TCP connections on port 502 (configurable). It supports connections from standard Modbus TCP client applications. Windows client software for basic testing is available for download here.
Upon receiving a connection request, the EM-482 checks its list of active clients. If the maximum list size (as per technical specifications) has not been reached, the new client is accepted.
Once connected, the EM-482 processes Modbus requests from the client. In RS-485 Slave Mode, it also accepts requests from a Modbus Master on the RS-485 bus.
The device analyzes each request based on the requested function and the client’s access rights (determined by passwords entered).
Blocked Requests: If a request is blocked due to insufficient rights, the EM-482 sends back a Modbus exception (default code 1).
Internal Requests: If the request addresses the EM-482 itself, it is processed internally, and a reply is sent back.
Redirection:
RS-485 Master Mode: Requests for other devices are converted (Modbus TCP/RTU/ASCII) and redirected to the RS-485 bus. The RS-485 indicator lights up while waiting for a response.
Remote Server: If configured, requests can be redirected to a remote Modbus TCP server via Ethernet or GSM/LTE.
If a valid response is received, the EM-482 forwards it back to the client.
Exception Illegal Function (Code 1) is returned for a request: Sent either by EM-482 (if insufficient rights for the request) or by the target device (if the request unsupported). Check the EM-482 settings (Protection group) for protection settings. Send the correct password to the EM-482 before using this request. Try allowing these requests, or try some other request.
Exception Gateway Path Unavailable (Code 10 or 0x0A) is returned for a request: Sent if the request cannot be redirected. Check the connection to the remote is configured and established (if the target should be requested using Modbus TCP). Check the Modbus Master mode is configured (if the target should be requested using Modbus RTU/ASCII). Check the Modbus address ranges in EM-482 settings for the redirection destinations.
Exception Target Device Failed to Respond (Code 11 or 0x0B) is returned: Sent if no response is received from the target device. Check the device settings match the EM-482 configuration for RS-485 (baudrate and parity in particular). Check the target device is powered on.
Some exception (not 1, 10 or 11) is returned: Sent by the target device if it could not perform the request or produce the response data. Check the device manual. Try some other request.
The data has been acquired, but the values seem wrong: Check the device manual. Ensure the Modbus device address and Modbus register address in the request are correct. Check the data formatting in the Modbus client software (which is sending this request). Try dividing the acquired value by 10, 100 or 1000.
Table 1 - Standard Modbus Exception Codes
Code
Exception
Description
1
ILLEGAL FUNCTION
The received function code cannot be processed
2
ILLEGAL DATA ADDRESS
The data address specified in the request is not available
3
ILLEGAL DATA VALUE
The value contained in the request data field is invalid value
4
DEVICE FAILURE
Unrecoverable error has occurred when the addressee has tried to perform the requested action
5
ACKNOWLEDGE
The addressee accepted the request and processed it, but it takes a long time
6
DEVICE BUSY
The addressee is busy processing the command. The client can retry the request later
8
MEMORY PARITY ERROR
The parity error was detected when the addressee has tried to read the extended memory
10
GATEWAY PATHS NOT AVAILABLE
The gateway cannot redirect the request, since there is no path (connection) to the addressee
11
TARGET DEVICE FAILED TO RESPOND TO GATEWAY
The gateway did not receive a response to the forwarded request, because the addressee did not respond in time
The EM-482 can be configured using any Modbus TCP client.
Connect: Use the EM-482’s IP address (configured manually or provided by the Wi-Fi access point, see its corresponding manual on how to check the address) and Modbus ID (default 111).
Enter Password: Write the password (default setup access password is in the parameter list, Protection group ) into the password registers (see Current Mode Parameters).
Verify Mode: If the password is correct, the Mode register will read 1 (Setup Mode).
Integer number (16 bit) in standard range of Modbus register values
1
Number
0 – 4294967295 in two registers, MSB part – first
Integer number, which value can exceed the limit for Modbus register (65535)
2
Character string
In every register – number of 0 to 255 - ASCII character code or 0 (the end of string)
A set of values, each of which is equal to the code of one character in the ASCII encoding. If the string is shorter than the maximum length, the code 0 is placed after the last character.
Max. length of string for this parameter
IP-address (IP-mask)
In every register – one byte (0 – 255)
Set of four byte of address IPv4, from left to right
4
MAC-address
In every register – one byte (0 – 255)
Set of six byte of address MAC-48, from left to right
6
Table 3 - Parameter Groups
Group
Description
Access
Address
Device description
Device and firmware identification
Any mode, read only
0 – 3
Current mode
Access and general commands controls
Password entry is available in any mode, command entry - only in setup mode (after password entry)
100 – 120
Current status
Interfaces and software modules operation, current time and statistics
Any mode, read only
121 – 177, 2000–2005
Changeable settings
Interfaces and features selection and configuration
Only in setup mode, reading or writing
300 – 899, 5250 – 5499
Active settings
The configuration being used by the device at the moment
In any mode, read only
2300 – 2899, 5500 – 5749
Saved settings
This set is saved regardless the power of the device and is used at restart
If the dynamic addressing is switched off, IP-address of the device in Wi-Fi network is equal to this value
300 – 303
Subnetwork mask*
IP-mask
255.255.255.0
It is used only with static IP-address
304 – 307
Gateway*
IP-address
192.168.0.1
It is used only together with static IP-address for communication with other networks
308 – 311
Switch on the dynamic addressing with a help of DHCP*
0 – 1
1
0 – for addressing on Wi-Fi access point network, the specified values of the IP address, mask and gateway are used;
312
1 – If DHCP server is available in the network, then IP address, mask and gateway are received from the server
Unused parameter
0
0
Should be 0 for compatibility
313
Switch on the use of server gateway DNS
0 – 1
1
0 – DNS of gateway is not used;
314
1 – The gateway DNS is used to determine the IP addresses of other servers, if they are specified by host names
IP-address of DNS server
IP-address
8.8.8.8
It sets IP-address of a DNS server
315 – 318
IP-address of additional DNS server
IP-address
0.0.0.0
0.0.0.0 – it is not used
319 – 322
Unused parameter
0
0
Should be 0 for compatibility
323 – 339
SSID – Wi-Fi access point*
Character string
EM-482 is connected to the given access point. Up to 32 characters
340 – 371
Wi-Fi access point password*
Character string
Up to 24 characters
372 – 395
Unused parameter
0
0
Should be 0 for compatibility
396 – 449
Modbus TCP Server
TCP connection port for Modbus TCP
1 – 65535
502
It is used for external connection to EM-482 via Ethernet for exchange via Modbus TCP protocol
450
Disconnect inactive clients
0 – 1
1
0 – incoming TCP connection is kept regardless of the time between requests from the client;
451
1 – disconnect clients that did not send requests for longer than a specified time
Max. request waiting time, s
0 – 600 000
90
Used if disconnection of inactive clients is selected
452 – 453
Unused parameter
0
0
Should be 0 for compatibility
454 - 456
Own Modbus-identifier of EM-482
0 – 247
111
0 – all queries are sent via Modbus to the Modbus network, the device registers are unavailable by Modbus;
457
1 - 247 – the device responds Modbus queries with this Modbus identifier without forwarding them on
RS-485 network
Bit rate via RS-485, bit/sec*
75 – 230 400
9 600
It is used in case of data exchange between the devices via RS-485, the same value for the devices on the same RS-485 bus cable
458 – 459
Unused parameter
1
1
Should be 1 for compatibility
460
Byte format when transmitting via RS-485*
0 – 5
5
It is used in case of data exchange between the devices via RS-485. See Table 7.1 for formats.
461
Waiting time for starting the Modbus RTU response, ms
0 – 60 000
200
It is used for transmissions via RS-485 in Modbus RTU mode. After transmission of query, if the first byte of the response was not received within this time interval, the waiting for the response is terminated. The response is always waited for at least the silence time between frames
462
Enable ASCII exchange mode in Modbus network
0 – 1
0
Exchange mode via RS-485, the same value for all units on the same RS-485 bus cable.
463
0 – RTU exchange mode (format: 1 start bit, 8 data bits, 2 stop-bits, parity bit, and stop bit or only 1 stop bit – total from 10 to11 bits);
1 – ASCII exchange mode (format: 1 start bit, 7 data bits, 2 stop-bits or parity bit and stop bit - total is 10 bits). The non-standard byte formats (register 461, values 4 and 5) are not available in this case, format 3 (2 stop bits) is used instead
Response time for subsequent Modbus ASCII character, ms
0 – 60 000
1 000
It is used in case of data transfer via RS-485 in Modbus ASCII mode. If you receive a response, if the next byte of the response was not received within this time interval, then the response waiting is stopped. Waiting is always not less than the transmission time of one character (depends on the transmission speed)
464
Connection to the cloud server
Mode of connection to the cloud server*
0 – 1
1
0: connection to the server is not used;
465
1: establish and maintain a connection to the data collection server
Cloud server connection port
0 – 65535
20502
The port to which the party is addressed, making connection between EM-482 and the server (see reg. 465)
466
Time of waiting for response from the cloud server, s
0 – 3 600
120
0 – the server silence time is not limited;
467
1–3600 – max. time of server silence after which the connection will be stopped and must be remade again
Delay time before reconnecting to the cloud server, s
0 – 30 000
15
It is used when connecting to the server. After losing connection to the server, the reconnection will be performed after the specified waiting time
468
Unused parameter
0
0
Should be 0 for compatibility
469 - 473
Enable setting the server address with a text string
0 – 1
1
This is used when connecting to the server.
469
0: the connection is made to a server with a fixed IP address specified in registers 470-473;
1: the connection is made to the server with the name specified in registers 474-509
Server’s IP address
IP address
0.0.0.0
This is used when connecting to the server, if setting the server’s address with a text string is disabled. IP address of a remote server, with which the connection is maintained
470 – 473
Cloud server address
Character string
modbus.overvis.com
It is used when connecting to the server, if the server address setting is turned on with text string. Address of the remote server with which the connection is supported.
474 - 509
The string of up to 36 characters can be indicated as address. This string should not have any spaces
Protection
Password for setup mode access
Character string
11111
It is used to access the configuration mode. The string of 5 to 10 characters in length can be indicated as password. This string should not have any spaces
510 – 519
Unused parameter
0
0
Should be 0 for compatibility
520 – 549
Password for writing permission via Modbus to the other devices
Character string
It is used to access devices connected to the EM-482, to request write or control functions that can change the status of these devices. The string up to 10 characters in length can be specified as password. This string should not have any spaces
550 – 559
Password for reading permission via Modbus
Character string
It is used to access devices connected to the EM-482, to request read functions, or to access the EM-482 registers, except for registers of version, password, mode and flags. The string up to 10 characters in length can be indicated as password. This string should not have any spaces
560 – 569
Unused parameter
0
0
Should be 0 for compatibility
570 – 571
Enable the protection mode against writing via Modbus
0 – 1
0
0 – Protection against recording is regulated with help of other parameters (password) or deactivated;
572
1 - Blocking of any queries for functions, excepting functions of Modbus 1, 2, 3, 4, 7, 17, 20
Enable the protection mode against reading via Modbus
0 – 1
0
0 – Protection against reading is regulated with help of other parameters (password) or deactivated;
573
1 – Blocking of queries for functions of Modbus 1, 2, 3, 4, 7, 17, 20, excepting reading using function 3 of registers of version, mode and tabs
Unused parameter
0
0
Should be 0 for compatibility
574
Miscellaneous
Unused parameter
0
0
Should be 0 for compatibility
575 - 629
Enable automatic restart of the Product
0 – 1
1
0: periodic restart is disabled;
630
1: the Product is restarted after a specified period of time
Restart time, min
5 – 7 200
120
Used when automatic restart is enabled.
631
Enable restart mode automatically only in the absence of connections
0 – 1
1
This is used if automatic restart is enabled.
632
0: the Product is restarted after a specified period of time since the start;
1: the Product is restarted after a specified period of time since the last MODBUS transmission
Modbus exception code generated when access is denied
0 – 255
1
0 – if the access to Modbus registers is denied, the response to the client is not returned;
633
1 – 255 – if you deny access to the client who sent the request, this exception code is returned
Modbus exception code generated when there is no response
0 – 255
11
0 – if there is no response from the addressee (Gateway Timeout), the response to the client is not returned;
634
1 - 255 – if there is no response from the request recipient, this exception code is returned to the client
Unused parameter
0
0
Should be 0 for compatibility
635
Modbus exception code generated if there is no connection to query addressee
0 – 255
10
0 – If there is no connection to the query addressee (Gateway Path Unavailable), response is not returned to the client;
636
1 – 255 – if there is no connection to the query addressee, this exception code is returned to the client
RS-485 transmission mode
0 – 1
0
0 – Master mode (Modbus Master): RS-485 is used to send queries;
637
1 – Slave mode (Modbus Slave): RS-485 is used to receive queries from additional client;
First Modbus-identifier of RS-485
1 – 255
1
Two parameters define a range of Modbus identifiers used for RS-485.
638
In the master mode the queries with addresses in this range (and also the broadcast ones with address 0) are sent via RS-485.
In the slave mode the queries with addresses in this range (and also the broadcast ones and the queries to EMC-482 address) are received via RS-485
Last Modbus-identifier of RS-485
1 – 255
255
same as above
639
Connection to the remote Modbus TCP server
IP-address of the remote server*
IP-address
192.168.0.112
It is used with enabled redirection of queries to a remote Modbus TCP server. IP-address of the remote server wherewith connection is maintained
640 – 643
Port of the remote server connection
0 – 65535
502
Port of the remote server to which the TCP connection will be established
644
Time to wait for response from remote server, ms
0 – 60 000
1 000
It is used during redirection of queries to the remote server. After the query transfer, if the correct response has failed to be received within this time interval, response waiting is stopped
645
Standby time to repeated connection to the remote server, s
0 – 240
20
It is used during redirection of queries to the remote server. After connection with the server is lost, the repeated connection will be performed after preset standby time
646
Remote server connection mode*
0 – 1
0
0: remote MODBUS TCP server is not used;
647
1: the connection to the remote MODBUS TCP server is established and automatically maintained
First Modbus-identifier of the remote server
1 – 255
1
It is used during redirection of queries to the remote server.
648
Two parameters define the range of Modbus identifiers used on the remote server.
Queries with addresses in this range (and also the broadcast ones with address 0) are sent to the remote Modbus TCP server
Last Modbus-identifier of the remote server
1 – 255
255
same as above
649
Unused parameter
0
0
Should be 0 for compatibility
650 – 729
Wi-Fi services
Period of search for the best Wi-Fi hotspot
0 − 72
4
0: do not search for access points with a better signal and don’t switch between them until the connection is lost; Other values: the number of hours until the search for the access point of the same name with better signal
730
Unused parameter
0
0
Should be 0 for compatibility
731 – 739
Product Name
Character string
Name to distinguish products from each other
740 – 779
The string of up to 36 characters can be indicated as address.
Unused parameter
0
0
Should be 0 for compatibility
780 – 799
User’s Settings
User’s settings and saved values
0–65535
0
They can be used for storing any product identification data, or filled in by MODBUS clients for storing and transmitting data to the server
Q: What is the default Modbus TCP port and device address?
A: EM-482 listens on TCP port 502 (configurable in register 450) and uses Modbus address 111 by default (configurable in register 457). The current IP address can be usually checked at the network router which provides the Wi-Fi access point for EM-482.
Q: How do I enter Setup Mode to change configuration?
A: Write the password (found on the device label) to registers 100-119. If correct, register 121 will read 1 (Setup Mode). You can then modify settings in the Changeable Settings registers (300-799).
Q: How do I save my configuration changes?
A: Write command 2 to register 120 to save (then restart EM-482 for the changes to take effect), or 4 to save and apply immediately (only for Modbus and user’s settings). Write 9 to cancel unsaved changes.
Q: I have saved the new settings, how do I restart EM-482 remotely?
A: Write command 1 to register 120 to restart. EM-482 will reboot and usually be available again in half a minute. You may need to reconnect then.
Q: How do I configure RS-485 communication parameters?
A: Key registers are:
458-459: Baud rate (default 9600)
461: Byte format/parity (see Table 7.1)
463: Protocol mode (0=Modbus RTU, 1=Modbus ASCII)
637: Transmission mode (0=Master, 1=Slave)
Q: What is the difference between Master and Slave RS-485 modes?
A: In Modbus Master mode (default), EM-482 sends queries to RS-485 devices (these queries come from Modbus TCP clients via Wi-Fi). In Modbus Slave mode, EM-482 receives queries from an external Modbus Master on RS-485 (these queries usually are intended for remote Modbus TCP server accessible via Wi-Fi). Use Slave mode when EM-482 should act as a slave device on an existing RS-485 network.
**Q: I have configured RS-485 and set EM-482 modbus device ID parameter to match my RS-485 device address. But I still get errors like Illegal address.
A: This can happen because EM-482 (configured this way) reads its own Modbus registers instead of redirecting the requests to your RS-485 device. Do not set EM-482 own Modbus ID in the Modbus TCP Server parameters to any of your devices addresses. However, reading registers of any device with ID other than this one (which is 111 by default) should work.
Q: Can I connect the RS-485 device if its protocol differs from Modbus?
A: No, the EM-482 supports only Modbus protocol transfers.
Q: Can I connect EM-482 to multiple remote Modbus TCP servers?
A: EM-482 supports connection to a single remote TCP server. If this server is itself a EM-482 converter, they can be configured as a chain, with each one connecting to the next EM-482 IP address. However, the delays are increased with the chain length. To connect several of the other Modbus TCP devices, a converter supporting multiple remote servers can be used (one from the EM-48x or MC-25x series, e.g. EM-483). Configure each remote connection in devices’s registers 640-649. The main parameters are the connection mode and the server IP address. Also, set Modbus ID range for each remote server to avoid extra traffic and delays.
Q: How do I reset the device to factory defaults?
A: Enter Setup Mode by writing the password, then write command 444 to register 120. All settings will be reset to factory defaults, including passwords. Restart EM-482 for the changes to take effect.
Q: How do I check the current firmware version?
A: Read register 1 for the firmware version number.
This page lists available software utilities for the EM-482 Protocol Converter. These tools are designed to help with device configuration, testing, and Modbus TCP communication.
Windows Modbus TCP Client Software (Novatek-Electro)
The Modbus TCP Client is a Windows application designed for basic communication and testing with network devices that support the Modbus TCP protocol. It enables reading and writing to device holding registers.
This application can also connect to other devices on the network, by using bridge and gateway devices (such as EM-482, EM-483, ET-485 converters, and MC251, MC252, EM-480, EM-481, EM-486 controllers).
Key features include:
Simple Interface: Fast connection to devices for viewing registers and modifying values.
Configuration Management: Save device configurations, including register mappings to a file.
Reusable Write Sets: Save sets of register write operations for repeated use.
Event Logging: Connection logs, data transfers, and errors, which can be exported to a file.
User firmware – the file can be uploaded via the WEB-interface or downloaded from the server;
Manufacturer firmware – the file is written by the Manufacturer and cannot be replaced. If the update fails (for example, due to power failure), this file is used for automatic recovery.
Any of these files can be retrieved from the EM-482 memory (to upload to another Product). Firmware can be updated from these files via the WEB-interface, or remotely by Modbus command.
The update files can be written to the EM-482 memory in 2 ways:
Upload from the client device using WEB interface
1.1 access the device using the browser (see Quick Start Guide);
1.2 open Files page;
1.3 if another file has already been uploaded to EM-482, delete it by clicking the Delete button;
1.4 click the file selection button in the User firmware row;
1.5 select the update file, for example, EM-482-1-1-10.FUS in the window that opens;
1.6 click the Upload button in the User firmware line.
1.7 wait until the file upload finishes.
Download from the server manually using MODBUS commands
2.1 connect to the device via MODBUS and enter the setup mode (see Configuration via Modbus);
2.2 to verify the version of the downloaded update file, read the header line in registers 2030 - 2061;
2.3 check if the file download is in progress by reading register 2004;
2.4 to download the newer version from the cloud server, write the value 64893 into the control command register 120;
2.5 control the file download by reading registers 2004 - 2005;
2.6 after download completion, double-check the version of the downloaded file in registers 2030 - 2061.
EM-482 firmware can be updated from the file in its memory in 2 ways:
Update manually using WEB interface
1.1 access the device using the browser (see Quick Start Guide);
1.2 open Files page;
1.3 press the Program button in the row of the needed firmware update file to start the firmware update from it.
Update manually using MODBUS commands
2.1 connect to the device via MODBUS and enter the setup mode (see Configuration via Modbus);
2.2 to verify the version of the downloaded update file, read the header line in registers 2030 - 2061;
2.3 to start the update from the file, write the value 65397 into the control command register 120.
Q: Will I lose my configuration or data during an update?
A: No, the firmware update to a newer version process is designed to preserve your device configuration, Modbus settings, and historical data. However, downgrading the firmware may revert the settings to factory defaults. In either case, backing up critical data is always recommended.
Q: The “Upload” button is not appearing in the Web Interface.
A: This can happen if some other file is already uploaded. Click the “Delete” button to free the memory.
Q: The firmware does not update automatically.
A: EM-482 does not support automatic updates. However, the firmware can be downloaded and updated from the server using two Modbus commands.
Q: The firmware update does not download at Modbus command.
A: This can happen if:
The device is already running the latest firmware.
The device does not have Internet access. Check your Wi-Fi and DNS settings.
The update server is temporarily unreachable.
Q: The device does not see / does not recognize the uploaded file.
A: This can happen if the file upload was interrupted. Try again, try different browser or use the firmware download from the server.
Q: The update process seems to hang.
A: The update process typically takes 1 minute. If it takes significantly longer:
Do not power off the device immediately.
Check the PWR red signal, if it is continuously blinking for an error, or the device is unresponsive for over 5 minutes, try a manual restart. If the internal firmware is corrupted, the device should enter the emergency update mode automatically.
Q: Can I downgrade the firmware?
A: Yes, you can install an older firmware version by manually uploading the older firmware file and initiating the update. However, the device settings are not always retained and may be reverted to factory defaults after firmware downgrade.
