Product manual

B Protocols TAC Xenta Server – Gateway, Technical Manual
180 (184) Schneider Electric Buildings AB, June 2011
04-00124-06-en
B.8.6 Multiple Read-Only Signals Per Group Variable
During normal operation each read-only signal should reflect the state
of its associated Group Variable on the C-Bus network. However, input
values are only updated in response to C-Bus events, so the value will
be “unknown” for 5 to 10 seconds after startup.
Generally only one read-only signal is assigned to monitor a Group
Variable, and its ON/OFF or LEVEL type is set to match that of the
corresponding group variable. Although it is possible to have more than
one input value monitoring a group variable, there is no real advantage
in doing so.
B.8.7 Read/Write Signal For A Group Variable
One Write-Only and one Read-Only signal can be associated with a sin-
gle Group Variable. In this case the read-only signal should normally
reflect back the state set by the write-only signal. However, if an exter-
nal C-Bus node also controls the Group Variable then the read and write
signals may differ. This can be used by the control system in 2 ways:
1 Propagate the manual switch change throughout the control sys-
tem by changing the write-only signal to correspond to the new
Group Variable state.
2 Cancel the external node change by re-enforcing the required con-
trol state onto the write-only signal. Note, however, that the Xenta
913 only sends messages onto the C-Bus when a signal changes,
so it will be necessary to first set the signal’s value to correspond
to the external node’s state before re-setting it to the required con-
trol state.
Note
• If an ON/OFF input value is incorrectly associated with a “dim-
mer” type group variable then the value will be ON for a
non-zero level, so a change to OFF will be delayed when the
group variable’s level is ramped to 0 over time.