Description
3Wire Dual-Master Isolated RS485 Hub
3Wire RS2M2 Dual Master Isolated RS485 Hub
3Wire RS2M2 is a two-channel isolated RS485 hub designed to allow two RS485 master devices to communicate with one or more RS485 slave devices without cross-interference. It ensures that slave responses are routed only to the corresponding master that initiated the request.
RS2M2 is useful when two independent systems need to read the same RS485 device network, such as when a PLC, SCADA system, BMS, energy monitoring gateway or IoTWatt 4.0 gateway must share access to power meters, controllers, sensors or Modbus RTU devices.
Master Ports Two RS485 master interfaces: MA1 and MA2
Slave Port One RS485 slave-device network interface: SLA
Protection 15kV ESD and 5kA lightning surge protection
Power Supply DC 9–30V with reverse polarity protection
Product Overview
Standard RS485 networks normally operate with one master polling one or more slave devices. When two masters are connected directly to the same RS485 bus, communication collision and response confusion may occur. RS2M2 solves this problem by managing communication between two RS485 masters and the shared RS485 slave network.
The RS2M2 provides transparent data transmission and supports master-slave protocols such as Modbus. Each communication port can be configured independently for baud rate and communication format, making the device flexible for different RS485 system requirements.
Positioning: Dual-master RS485 hub for safe sharing of one RS485 slave network by two independent master systems.
Typical Communication Flow
Two RS485 masters connect to the MA1 and MA2 ports. The shared RS485 slave network connects to the SLA port. The RS2M2 manages the communication so that slave responses are returned to the correct master.
1 Master #1
2 Master #2
3 RS2M2 Hub
4 RS485 Bus
5 Slave Devices
Key Features
Dual RS485 Master Support
Allows two RS485 master devices to communicate with one or more slave devices without direct cross-interference.
Correct Response Routing
Slave responses are sent only to the corresponding master that initiated the request.
Modbus Compatible
Supports master-slave communication protocols such as Modbus RTU.
Independent Port Configuration
Each of the three communication ports can be configured independently for baud rate and communication format.
Transparent Data Transmission
Designed for transparent RS485 data transfer without requiring application-level protocol conversion.
High Slave Node Capacity
Supports large RS485 slave networks; up to 175 nodes depending on configuration and application design.
Electrical Isolation
Provides complete electrical isolation between communication and power, plus isolation between master and slave interfaces.
Robust Protection
Includes anti-static, anti-lightning and anti-surge protection for industrial communication environments.
Real-Time LED Monitoring
Each communication port includes LED indication for quick status and activity checking.
Typical Applications
Shared Meter Reading
Allow both a local PLC / BMS and an IoTWatt 4.0 gateway to read the same RS485 Modbus meters.
SCADA + Energy Monitoring
Use one master port for SCADA and the second master port for EMS, energy dashboard or cloud monitoring.
Industrial Automation
Share access to RS485 devices between PLCs, HMIs, data loggers and remote monitoring systems.
Remote Monitoring
Connect an additional monitoring gateway without disturbing the existing RS485 master system.
Alarm and Access Control
Suitable for RS485-based alarm, security, access control and control-system applications.
Retrofit Projects
Add a second master to an existing RS485 network without major rewiring or system replacement.
Interface and Function
RS2M2 has three communication interfaces. MA1 and MA2 are used for the two RS485 master devices, while SLA is used for the RS485 slave-device network. The device is designed so both masters can access the slave network while reducing communication interference.
| Interface |
Terminal / Identification |
Function |
| Power Input |
VCC |
Connect to positive (+) terminal of DC power supply, DC 9–30V. |
| Power Negative |
GND |
Connect to negative (–) terminal of DC power supply. |
| RS485 Slave Network |
485A / 485B |
Connect to the RS485 A and B terminals of the slave-device network. |
| RS485 Master 1 |
485A1 / 485B1 |
Connect to the RS485 A and B terminals of Master #1. |
| RS485 Master 2 |
485A2 / 485B2 |
Connect to the RS485 A and B terminals of Master #2. |
| Signal Ground |
GND |
RS485 ground reference / grounding port, where required by installation design. |
| Setting Button |
SET |
Used for device setting / configuration function. |
Wiring note: Connect “A” to “A”, “B” to “B” and GND to the grounding / reference terminal as required. Always confirm the A/B labelling convention of each connected device because some manufacturers label RS485 polarity differently.
Technical Specifications
| Category |
Specification |
| Product Type |
Dual-master isolated RS485 hub |
| Communication Type |
Isolated RS485, master-slave communication |
| Communication Protocol |
Modbus protocol and other similar master-slave protocols |
| Data Transmission |
Transparent transmission |
| Master Interfaces |
Two RS485 master ports: MA1 and MA2 |
| Slave Interface |
One RS485 slave-device network port: SLA |
| Slave Node Capacity |
Up to 175 nodes depending on configuration and application design |
| Communication Distance |
Up to 1000m under suitable RS485 wiring and installation conditions |
| Baud Rate |
1200bps to 115200bps; default 9600bps |
| Data Format |
8 data bits, no parity, 1 stop bit by default; stop bit and parity can be set |
| Processor Architecture |
32-bit microcontroller with high-speed optocouplers |
| Isolation |
RS485 isolation voltage 2500V; complete isolation between communication and power; full isolation between master and slave interfaces |
| Protection Level |
RS485 anti-static, anti-lightning and anti-surge protection; each wire with 600W lightning / surge protection and ±15kV ESD protection |
| Power Input |
DC 9–30V |
| Minimum Required Current |
≥ 100mA |
| Maximum Voltage Limit |
Do not exceed 35VDC; exceeding this may damage the circuit |
| Power Protection |
Built-in overcurrent and reverse polarity protection; reverse connection will not damage the module |
| LED Indicators |
LED indicators for each communication port and operating status |
Specification note: The overview page states slave communication support up to 175 nodes, while the interface section states a maximum of 120 slaves. For project design, confirm the final node count based on baud rate, cable length, termination, device loading and actual site conditions.
Why Use RS2M2?
RS2M2 is useful when an existing RS485 network already has one master, but a second master must also read data from the same slave devices. Directly connecting two masters to the same RS485 bus can create collisions and unreliable communication. RS2M2 provides a controlled, isolated way to share access.
- Allows two independent RS485 masters to read the same slave network.
- Reduces cross-interference between master devices.
- Routes slave responses to the correct requesting master.
- Supports Modbus RTU and other master-slave protocol applications.
- Useful for adding energy monitoring without disturbing existing PLC / SCADA communication.
- Provides isolation and surge / ESD protection for industrial environments.
- Supports retrofit projects where existing RS485 devices must be shared.
Integration with IoTWatt 4.0
RS2M2 is useful in IoTWatt 4.0 deployments where existing Modbus meters are already connected to a PLC, SCADA or BMS master. Instead of disconnecting or reworking the existing communication system, RS2M2 can allow IoTWatt 4.0 to become the second master for data collection.
- Use MA1 for the existing PLC, SCADA or BMS master.
- Use MA2 for IoTWatt 4.0 gateway, RS2LAN, RS2MQTT, RS2WLAN or another data collector.
- Connect the existing Modbus meters or slave devices to the SLA port.
- Collect energy, demand, power quality or equipment data without replacing the existing RS485 system.
- Support digital energy audit, EECA reporting, equipment dashboards and energy analytics.
Recommended Deployment Checklist
- Confirm the existing RS485 master and the proposed second master.
- Confirm slave-device protocol, normally Modbus RTU or similar master-slave protocol.
- Confirm baud rate, parity, stop bit, slave IDs and register map.
- Confirm RS485 A/B polarity for every connected device.
- Confirm RS485 cable length, shielding, termination and grounding approach.
- Confirm the number of slave devices and total bus loading.
- Confirm polling intervals so both masters do not overload the slave network.
- Confirm DC 9–30V power supply with minimum 100mA available current.
- Do not exceed 35VDC power input.
- Test each master independently before enabling simultaneous operation.
RS2M2 Supply, Configuration and IoTWatt 4.0 Integration
Saturn Pyro supports 3Wire RS2M2 dual-master isolated RS485 hubs for Modbus RTU meter sharing, PLC / SCADA / BMS integration, energy monitoring, RS485 retrofit projects, remote monitoring and IoTWatt 4.0 deployments in Malaysia.
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