Easy BACnet
BACnet vs Modbus — what is the difference?
Updated 11 October 2026
Both move data to and from building and industrial equipment, but they work at different levels. BACnet is object-oriented and self-describing: devices can be discovered on the network, and every point carries a type, a name and units. Modbus is a simple register protocol: it gives you numbered registers and nothing else — no discovery, no names, no units. As a rule of thumb, BACnet runs the HVAC controls and the building management system; Modbus is common on meters, VFDs, generators, PLCs and packaged equipment.
Discovery: ask the network vs sweep it
BACnet has discovery built in. A tool broadcasts a Who-Is and each device that receives it answers with an I-Am, so you can build a device list in seconds without knowing what is out there. Modbus has nothing like it: you must already know a device's IP address and unit ID (or its slave address on an RS-485 bus), or poll address by address until something answers.
Meaning: named points vs bare registers
A BACnet point is an object such as Analog Input 3 with an
Object_Name (say AHU-1 SA-T), a Present_Value,
engineering units and status flags, so the device tells you what the number means. A
Modbus holding register is just address 40007 containing 685; whether that is
68.5 °F, 685 kPa or half of a 32-bit value split across two registers is
something you work out from the vendor's register map.
Addressing
| BACnet | Modbus | |
|---|---|---|
| Identity | Device instance (must be unique across the whole BACnet internetwork) | IP + unit ID (TCP), or slave address 1–247 (RTU) |
| A point | Object type + instance (e.g. AI 3) | Register type + number (e.g. holding register 40007) |
| Self-describing | Yes — name, units, status | No — just a number |
| Discovery | Who-Is / I-Am | None |
| Wiring | BACnet/IP on Ethernet, MS/TP on RS-485 | Modbus TCP on Ethernet, Modbus RTU on RS-485 |
Where you meet each
BACnet dominates air handlers, VAV boxes, rooftop units, chillers and the BAS head-end (Niagara, Metasys, Desigo CC, WebCTRL and the rest). Modbus is everywhere on power and BTU meters, generators, PV inverters and OEM skids; many VFDs and boilers offer both. Plenty of buildings run both, with the head-end or a protocol gateway mapping Modbus registers onto BACnet objects.
Which app do I use?
Use Easy BACnet for BACnet IP equipment. For Modbus gear there is a sister app, Easy Modbus, built the same way — and its own write-up of Modbus vs BACnet covers the same ground from the Modbus side.
Check it on your own network. Easy BACnet is a free Android app that finds BACnet IP devices and reads their points in a couple of taps.
Get it on Google Play