Project Overview
A UK-based water treatment company needed to connect hundreds of legacy Modbus RTU flow meters and pressure sensors to their new cloud-based SCADA system. InnovChip designed a high-performance Modbus RTU to TCP gateway that transparently bridged serial and Ethernet networks with sub-millisecond latency.
Client
Industry: UK Water Treatment & Utility Company
Project Duration: 8 weeks
Budget: £28,000
Industry
Water & Wastewater Treatment / Industrial SCADA
Challenge
- 350+ legacy Modbus RTU devices (flow meters, pressure sensors, valve actuators) spread across 8 pumping stations
- Devices used mixed baud rates (9,600 to 115,200 bps) and multiple parity settings
- Maximum gateway latency under 10ms required for real-time pressure control loops
- Must support simultaneous connections from up to 5 Modbus TCP masters (SCADA, local HMI, backup systems)
- Transparent mode required — no configuration changes on existing RTU devices
- Built-in diagnostics for field troubleshooting
- Industrial temperature range (-20°C to 70°C) and DIN-rail mounting
Solution
- MCU: STM32F767 (Cortex-M7 at 216MHz) with dual Ethernet MAC
- Serial: 4 independent RS-485 channels, each with dedicated UART + DMA
- Ethernet: 2x 100Base-TX ports (for daisy-chain topology)
- Firmware:
- Low-latency RTU frame parsing using hardware UART idle-line detection
- Multi-master TCP arbitration with round-robin fairness
- Configurable address mapping and RTU slave routing
- Protocol debugging mode with timestamped packet capture
- Configuration: Web-based management interface (HTTP server on-device)
- Management: SNMP v2c for integration with client’s network monitoring system
- Power: 12-48V DC wide input with galvanic isolation (2.5kV)
- Certification: CE, UKCA, and EN 61000-6-2 (industrial immunity)
Technical Details
| MCU | STM32F767ZI (Cortex-M7 @ 216MHz) |
| RAM | 512KB SRAM + 32MB SDRAM |
| Flash | 2MB internal + 8MB external NOR |
| RS-485 Channels | 4x isolated (2.5kV), up to 115,200 bps |
| Ethernet Ports | 2x 100Base-TX, auto MDIX |
| Forwarding Latency | < 1ms (RTU → TCP), < 3ms (TCP → RTU with 5 masters) |
| Max TCP Connections | 10 simultaneous (configurable) |
| Max RTU Nodes per Channel | 32 (RS-485, multi-drop) |
| RTU Buffer | 2KB dedicated per channel |
Result
- 120 gateways deployed across 8 pumping stations, connecting 350+ RTU devices
- Average forwarding latency: 0.4ms RTU→TCP, 1.1ms TCP→RTU (well under 10ms requirement)
- 100% compatibility with all existing Modbus RTU devices — zero field changes needed
- Web-based diagnostics reduced field troubleshooting time by 70%
- SNMP integration reduced unplanned downtime through proactive alerts
- All 120 units passed CE/UKCA certification on first submission
- Daisy-chain topology saved £15,000 in Ethernet switch hardware costs