Modbus defines registers and a master/slave model: that is common to both variants. What differs is the transport. Modbus RTU runs over a serial link (RS485, sometimes RS232); Modbus TCP runs over Ethernet/IP. The functions and data are identical — a meter exposes the same registers either way.
Modbus RTU vs Modbus TCP
Two variants of the same protocol — which one, for which use?
One protocol, two transports
Side by side
| Modbus RTU | Modbus TCP | |
|---|---|---|
| Medium | Serial RS485 / RS232 | Ethernet / IP |
| Model | Master / slave | Client / server |
| Addressing | Slave address (1–247) | IP + Unit ID |
| Speed | 9600–115200 baud | 10/100 Mbit/s and up |
| Distance | up to ~1200 m (RS485) | IP network (LAN/WAN) |
| Wiring | 2-wire twisted pair | Ethernet |
| Best for | field, local meters/sensors | network integration, multi-site |
Which to choose
RTU still rules in the field: cost-effective, multidrop on a single RS485 bus, ideal for nearby meters and sensors. TCP takes over as soon as you integrate with the network, cross IP distances or link several sites. The two often coexist. The WBox gateway handles both via the Modbus driver, and even acts as a serial ⇄ TCP gateway. You can then route Modbus to BACnet or MQTT.
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