M2MB Session Slave / Gateway
The M2MB Session Slave / Gateway connects the high-speed M2MB backbone to standard Modbus RTU slave devices or complete RTU slave networks.
It receives session-wrapped Modbus requests from the backbone, removes the session layer, and forwards the original Modbus RTU frame to the connected slave device or slave segment.
When the RTU slave replies, the gateway remembers which session master initiated the request and routes the response back to the correct originator.
The Session Slave / Gateway provides the session-aware bridge between M2MB and conventional RTU slave equipment. The connected RTU slaves do not need to understand M2MB.
What the Session Slave / Gateway does
In a normal RTU network, only one master can safely control the bus. M2MB changes this by moving the multi-master handling onto the backbone while keeping the local slave side compatible with standard Modbus RTU devices.
Receives session traffic
Accepts requests from many Session Masters over the shared M2MB backbone.
Forwards standard RTU
Removes the session header and sends the original Modbus frame to the target RTU slave network.
Routes replies correctly
Remembers each request origin so replies return automatically to the correct master.
Shared or dedicated slave connections
A Session Slave / Gateway can be used in different ways depending on the existing installation.
- Shared RTU segment: one gateway connects to a complete multi-drop RTU slave network.
- Dedicated RTU slave: one gateway connects to an individual RTU slave device.
- Mixed architecture: some slaves can be grouped, while others use individual gateways.
Flexible baudrate structure
Each slave segment connected to a Session Slave / Gateway uses its own local Modbus RTU baudrate. Slaves connected to the same shared RTU segment must use the same baudrate, as in any normal RTU network. However, a slave connected through its own individual Session Slave / Gateway can run at a different local baudrate.
- Example: three RTU slaves on one shared Session Slave all run at 9600 baud
- A fourth RTU slave on an individual Session Slave can run at 115.2 kbit/s
- All of them communicate through the same high-speed M2MB backbone
Live device access
M2MB is designed to transport live Modbus transactions rather than forcing all data through copied or shadow registers inside a gateway. The Session Slave forwards requests to the real RTU device and routes the actual reply back to the requesting master.
This keeps the system behaviour close to normal Modbus RTU while allowing many independent masters to share the same infrastructure.
Many conventional “multi-master” Modbus solutions operate by polling, caching, or multiplexing traffic between masters and slaves.
M2MB instead transports live Modbus RTU transactions over a deterministic session-aware backbone, allowing independent masters to access real slave devices dynamically rather than through copied gateway data.
In many ways, the Session Slave / Gateway behaves more like a transparent transport bridge than a traditional protocol gateway.
Deterministic arbitration
The M2MB backbone uses a field-proven arbitration system that prevents packet loss when multiple masters or slaves attempt to start transmitting at the same time. One transmitter wins the bus, while others withdraw and retry without corrupting the active packet.
Typical applications
- Connecting a group of VFDs to multiple HMIs or controllers
- Sharing a Modbus I/O network between a PLC, logger, and service tool
- Adding remote access to an existing RTU slave network without replacing devices
- Separating slow legacy RTU devices from faster modern devices while using one backbone
- Building modular machine networks using standard twisted pair cable
Beyond tablet counting equipment
XIAC Australia's core product range is focused on tablet and capsule counting machines, but the M2MB communication system was designed for general industrial Modbus RTU networks that need more than one master.
This includes systems with local and remote HMIs, data loggers, service laptops, SCADA systems, and distributed controllers. These requirements are common in pharmaceutical machinery, but they are equally valid in many other Modbus RTU installations.