The reason for TAC dummy nodes and the logic behind the number of dummy nodes created.
- TAC Vista System Plug-In
TAC dummy nodes are added to Xenta groups automatically in the LNS network. The dummies are made after group bindings have been created.
The TAC dummy nodes are created when group bindings are made. For more information about group bindings see Verifying Xenta Group Bindings in an LNS system.
Vista requires that the TAC Group and the TAC Xenta group differ in the number of devices. If you only have one Xenta group in your system, TAC Vista System Plug-In will create a dummy device and use its tag_0 (also first row of the address table) in the group binding for the TAC Group. This will allow Vista to differentiate between the TAC and Xenta groups. Notice that in both LonMaker and NL220, this dummy node that is created to represent a second Xenta group appears to be located in the same Xenta Group as the rest of the controllers. This is fine, the system plug-in is not going to create a new group to put it in, just realize why the dummy node is there. Modules do not count in the group bindings therefore the example below only has three devices in Xenta group 1.
Xenta Groups must consist of at least three Xenta devices. If you only have two Xentas in a Xenta group, TAC Vista System Plug-In will also use a dummy device, since a binding between just two devices is not considered a group binding. To create a group binding, a third device is needed. Consequently, you will need two dummy devices if you only have one Xenta in your Xenta group. Thus, if just one Xenta device exists in a single Xenta group, three dummy devices will be needed: one to separate the TAC group binding from the Xenta group binding and two more to form a Xenta group.