KNX

KNX is the open standard for home and building control that KNX Association maintains and that more than 500 manufacturers build devices for. A KNX installation is a network of small devices, each with an individual address such as 1.1.10: wall switches, push-buttons, dimmers, blind actuators, heating valves, presence detectors, weather stations and meters. They do not poll each other. A device sends a group telegram to a group address such as 1/2/3, and every device whose group objects listen to that address acts on it: the push-button writes “on”, the light switches on, and the visualization updates. The value is encoded by a datapoint type (DPT), for example 1.001 for on and off or 9.001 for a temperature in °C, and ETS, KNX Association’s engineering tool, links group objects to group addresses when a project is commissioned.

Most devices sit on twisted pair (TP1), a two-wire bus that also powers them, and some on radio. KNXnet/IP (ISO 22510) connects the bus to IP networks: IP interfaces give clients a tunnelling connection to a line, IP routers route telegrams between lines over multicast, and KNX IP Secure and KNX Data Secure add authentication and encryption. Visualizations, home automation servers, building management systems and gateways all reach KNX through KNXnet/IP.

Where you meet it

• Homes, offices, hotels, schools and hospitals: lighting, blinds and shading, heating and cooling per room, presence and scenes
• Building management and smart home platforms such as Home Assistant and openHAB, which talk to KNX through an IP interface
• Energy in buildings: meters, heat pumps, charging points and load control, next to BACnet and Modbus in the same plant room
• Commissioning and service: finding IP interfaces, watching group telegrams, checking values and secure installations on site

Quickstart

From the command line

Download knxctl from GitHub Releases, or go install github.com/otfabric/knxctl@latest:

# Which KNXnet/IP interfaces and routers are on the network?
knxctl discover
knxctl describe 192.168.1.10

# Watch every group telegram, passively, decoding two groups
knxctl monitor -g 192.168.1.10 --map 1/2/4=9.001 --map 1/2/3=1.001

# Read a temperature, then switch a light
knxctl group read 1/2/4 --dpt 9.001 -g 192.168.1.10
knxctl group write 1/2/3 on -g 192.168.1.10

# Encode and decode datapoint types and frames, offline
knxctl dpt encode 9.001 21.5
knxctl decode 061004200015040100001100bce0110a0a03010081

# A simulated KNXnet/IP interface to try all of this against
knxctl serve --object 1/2/3:1.001=off --object 1/2/4:9.001:CRT=21.5

knxctl sends nothing to the KNX network unless the command says so: discovery talks only to the IP interface, monitoring only listens, and only the group write, respond, answer and read commands send telegrams, after they validate the address, type and value. Output is text, a table or JSON with stable exit codes.

From Go

go get github.com/otfabric/go-knx

Group communication through a KNXnet/IP interface (abridged from the go-knx README):

c, err := client.DialTunnel(ctx, "192.168.1.10", nil)
if err != nil {
  return err
}
defer c.Close()

// Switch on (DPT 1.001), then write a temperature (DPT 9.001).
err = c.GroupWrite(ctx, knx.MustParseGroupAddress("1/2/3"), true)
err = c.GroupWrite(ctx, knx.MustParseGroupAddress("1/2/4"), 21.5, client.WithDPT("9.001"))

// Watch group telegrams.
sub := c.Subscribe(64, knx.MustParseGroupAddress("1/2/3"))
for t := range sub.C() {
  fmt.Println(t.Source, t.Group, t.Service, t.Value.Data)
}

The same library runs the other side: a KNXnet/IP server with virtual devices whose group objects store written values and answer reads, which ETS-style tools, Home Assistant through xknx, Calimero and knxd connect to like to an IP interface.

What go-knx and knxctl support