My KNX items have "???" as value even though my gateway is connected. Only a few show their value. What can I do?

Answer

KNX is an event-/telegram-based protocol. The server needs to receive a value first, before it knows the state of the group address. "Read on reconnect" in the Telegram Definitions can be set to read the value of a group address either on start up of the server or right after reconnecting to an interface. The server will send out READ telegrams to all these group addresses, which do have this flag set. If the actor is programmed that way, it will send a RESPONSE telegram. The value of this one will be held in the server until next data change.

Please note that there are 4 telegrams sent out per second and interface (250ms is default value), so the bus will not be overloaded.