KNX

KNX is the field bus of building automation: lighting, blinds, heating, ventilation. inSCADA supports KNXnet/IP natively — no separate gateway application is involved.

Addressing

A KNX group address is not a byte offset, so start address is not used. The hierarchy sits like this:

Level	What it carries
Connection	An IP interface, or the routing backbone
Device	A logical container — KNX has no device address
Frame	A main/middle group from ETS
Variable	A group address and its DPT

Device is not an address here

On other protocols a device corresponds to a station address; on KNX it does not. What is addressed on the bus is the group address, so a device only groups variables together and carries the polling interval.

Connection modes

Mode	What it does
TUNNEL_UDP	A UDP tunnel to a KNXnet/IP interface (the default)
TUNNEL_TCP	The same over TCP
ROUTING	Joins the routing backbone by multicast

In routing mode, with no address given, the standard multicast group 224.0.23.12 is used; the default port is 3671.

Connection fields

Field	Default	Description
Individual Address	—	inSCADA’s own address on the bus
Requested Address	—	The address to ask the interface for on a tunnel
Local Address	—	Which adapter to go out of, on a host with several
NAT Mode	off	For connections behind NAT
Min Send Interval (ms)	50	The shortest gap between two telegrams
Read Timeout (ms)	2000	How long a read response is waited for
Initial Read Interval (ms)	250	The gap between the initial reads at startup
Router Check Interval (s)	30	The poll interval in routing mode
Heartbeat Interval / Timeout / Retries	60 s / 10 s / 3	The tunnel’s liveness check

Think before lowering Min Send Interval

The KNX bus is a narrow line. The default 50 ms stops consecutive writes from swamping it. In a scenario that drives many points at once, lowering this can make telegrams drop.

Variable fields

Field	Description
Group Address	Where a write goes
Status Group Address	The actuator’s feedback address — this is what is read
Listen Group Addresses	Further addresses carrying the same value
DPT	The data point type
DPT Field	Which field of a composite DPT
Type	FLOAT, INTEGER, BOOLEAN or STRING
Status Only	Read-only
Expire (s)	How long before the value is considered stale

A group address is accepted in all three of KNX’s spellings: 1/2/3, 1/515 and 2563 are the same address.

The write and read addresses are usually different

A command to an actuator goes to one address and its state comes back on another. Group Address is where the command goes; Status Group Address is where the truth is read. Assuming they are the same and defining only the first leaves a value on screen that never updates — the most common KNX mistake.

The address and the DPT are checked at the save: a mistyped address would be a variable no telegram ever reaches, and a DPT the library does not know one that is never decoded. Both are refused then rather than found later by silence.

Discovering interfaces

inSCADA can find the KNXnet/IP interfaces and routers on the network, so a connection’s mode, address and port are picked from a list rather than typed. The search does not leave the local network.

Importing from an ETS project

Uploading an ETS project file reads its group addresses and DPTs. There are three steps:

Step	What it does
Read	Extracts the project’s group structure and addresses
Audit	Lists the problems before anything is imported
Plan	Shows which frames and variables would be created

The file is not kept

None of the three steps stores or logs anything from the ETS file. The plan you pick is applied by the wizard through the ordinary batch endpoints — so what gets created is decided where it always is.

Related

• Connections — defining a connection
• BACnet — the other building automation protocol