Buildings and HVAC
The language of HVAC and building plant. Read the BACnet page
Reference
Protocol Reference
The standards, ports, addresses and limits behind the eight protocols IoTServa reads, in one place. Public-standard facts only, with sources.
Specifications at a Glance
| Protocol | Standard | Medium | Topology | Range | Data Model |
|---|---|---|---|---|---|
| BACnet | ASHRAE 135 / ISO 16484-5 | IP networks (BACnet/IP over UDP, BACnet/SC over secure WebSocket) or RS-485 (MS/TP) | Peer to peer, routed between networks | Building and campus LAN | Objects with properties: Analog Input, Analog Value, Binary, Multi-state, Schedule, Trend Log |
| Modbus | Modbus Application Protocol (Modbus Organization) | RS-485 or RS-232 (RTU), Ethernet port 502 (TCP) | Client and server (master and slave) | Plant floor and switch room | Four tables: coils, discrete inputs, input registers, holding registers |
| KNX | ISO/IEC 14543-3, EN 50090 | Twisted pair (TP), KNX IP, KNX RF | Line and area bus, linked by couplers | A building or campus, with areas and lines linked over KNX IP | Group addresses (for example 1/2/5) carrying typed datapoints (DPT) |
| DALI | IEC 62386 (DALI Alliance, with DALI-2 and D4i certification) | Two-wire bus carrying power and data, read through a DALI gateway or controller | Bus, star or mixed wiring (loops not allowed), one bus power supply per line | Up to 300 m between the furthest devices on 1.5 mm2 cable, per DALI line | Control gear (drivers) and control devices (sensors, buttons), addressed by short address, group and scene |
| Serial Bus | TIA/EIA-485 and TIA/EIA-232 electrical layers, carrying protocols such as Modbus RTU and BACnet MS/TP | Serial cable: shielded twisted pair for RS-485, point-to-point for RS-232 | RS-485: multidrop daisy chain with termination at both ends. RS-232: one device per port | RS-485: about 1200 m at 100 kbit/s or lower, shorter at higher speeds. RS-232: about 15 m by the standard, longer at low baud rates on good cable | A master polls devices by address, one request at a time; the electrical layer carries the bytes, a protocol on top gives them meaning |
| MQTT | OASIS MQTT 3.1.1 (ISO/IEC 20922) and MQTT 5 | TCP and TLS (port 8883), WebSocket | Publish and subscribe through a broker | Anywhere with IP reachability | Topic strings with free-form payloads, optionally Sparkplug B |
| LoRa | LoRaWAN (LoRa Alliance) on LoRa modulation, AS923 plan in Malaysia | Sub-GHz radio to a gateway, then IP backhaul | Star of stars: devices, gateways, network server | Kilometres in open terrain, less indoors | Small uplink frames on a port, decoded by a payload decoder |
| BLE | Bluetooth Low Energy (Bluetooth SIG) | 2.4 GHz radio to a BLE gateway, then IP backhaul | Advertisers and scanners, or connected peripherals | Metres to tens of metres indoors (Bluetooth 5 Coded PHY reaches further in open line of sight) | Advertising data, or GATT services and characteristics |
Key Numbers and Where They Come From
| Protocol | Item | Value | Source |
|---|---|---|---|
| BACnet/IP | Default UDP port | 47808 (0xBAC0) | ASHRAE 135 |
| BACnet | Cross-subnet broadcasts | Need a BBMD, or a BACnet router between BACnet networks | ASHRAE 135 |
| Modbus TCP | Default TCP port | 502 | Modbus Organization |
| Modbus RTU | Device addresses | 1 to 247, one master per line | Modbus over Serial Line |
| Modbus RTU | Character frame | 11 bits: start, 8 data, even parity, stop (default) | Modbus over Serial Line |
| Modbus RTU | Frame separation | Silence of at least 3.5 character times | Modbus over Serial Line |
| RS-485 | Loads per line | 32 unit loads, up to 256 nodes with one-eighth unit load parts | Texas Instruments |
| RS-485 | Cable length | About 1200 m (4000 ft) at 100 kbit/s or lower | Texas Instruments |
| RS-485 | Termination | 120 ohm at each end of the trunk | Texas Instruments |
| RS-485 | Common-mode range | -7 V to +12 V | Texas Instruments |
| RS-232 | Typical limit | Point to point, about 15 m (2500 pF cable capacitance) | TIA/EIA-232, Modbus over Serial Line |
| DALI | Bus speed | 1200 bit/s | DALI Alliance |
| DALI | Devices per line | 64 control gear and 64 control devices | DALI Alliance |
| DALI | Control gear addresses | Short addresses 0 to 63, plus groups and scenes | DALI Alliance |
| DALI | Standard | IEC 62386, with DALI-2 and D4i certification programs | DALI Alliance |
| KNX | Group address | Written main/middle/sub such as 1/2/5, named in the ETS project | KNX Association |
| MQTT | Default ports | 1883 plain, 8883 over TLS | OASIS MQTT 3.1.1 |
| MQTT | QoS levels | 0 at most once, 1 at least once, 2 exactly once | OASIS MQTT 3.1.1 |
| LoRaWAN | Malaysia regional plan | AS923, listed as AS923-1 (confirm with the supplier) | LoRa Alliance |
| LoRaWAN | Device classes | Class A, B and C | LoRa Alliance |
| BLE | Band | 2.4 GHz, short range through gateways | Bluetooth SIG |
Limits are the standard's figures. Real installations are set by cable, devices and the manufacturer, so always check the device manual.
Serial Settings You Will Meet Most
| Baud Rate | Data Bits | Parity | Stop Bits | Where You See It |
|---|---|---|---|---|
| 9600 | 8 | Even | 1 | Modbus RTU default and the most common starting point |
| 19200 | 8 | Even | 1 | Common on meters and drives, and the highest speed that still uses 3.5 character times |
| 9600 | 8 | None | 2 | A frequent vendor variant, because no parity needs two stop bits for 11-bit frames |
| 38400 | 8 | None | 1 | Used by some newer meters and sensors, check the manual |
Both ends must match exactly. A wrong setting looks like a dead device.
Go Deeper
Meters, Drives and PLCs
Meters, drives and PLCs, finally on one map. Read the Modbus page
Lighting
Luminaire-level lighting data, read through the DALI gateway. Read the DALI page
Serial Lines
RS-485 and RS-232 devices, read at the edge and sent upstream as clean tags. Read the Serial Bus page
Have Devices on These Protocols? Request a Pilot.
Tell us which protocols are on site. We will scope a pilot that reads your real devices.