What is Modbus?

Modbus is a simple, royalty-free serial protocol introduced by Modicon in 1979. It survives because it's easy to implement and supported by almost every industrial vendor. The modern variants — Modbus RTU and Modbus TCP — cover both serial and IP deployments.

How it works. Modbus uses a client/server model (historically called master/slave). A client polls a device for the contents of numbered registers: coils and discrete inputs for on/off states, holding and input registers for values like a temperature or a kWh reading. There's no built-in security and no self-description — you need the device's register map to know what each address actually means.

Modbus RTU vs Modbus TCP. RTU is the original serial form, over RS-485 or RS-232, with compact binary frames; it's common on meters and legacy equipment. TCP wraps the same data model in TCP/IP over Ethernet, which is easier to integrate and needs no serial wiring. A serial RTU device reaches an IP network through a Modbus gateway.

Where you find it in buildings. Energy meters, submeters, water meters, variable-speed drives, and any older equipment whose vendor never moved up to BACnet or OPC UA. It's also common across industrial sites and energy infrastructure.

Modbus vs BACnet. BACnet is purpose-built for building automation and describes itself; Modbus is simpler and faster to implement but carries no context — just numbers at addresses. Plenty of buildings run both: BACnet for the BMS, Modbus for the meters.

How FrostLogic reads Modbus. FrostLogic Explore reads Modbus TCP natively; serial RTU is supported through a gateway. As with all our ingest, the connection is read-only by default, and we map each register to a physical meaning — so a number at an address becomes a sensor you can reason about.