Product manual

TAC Xenta Server – Gateway, Technical Manual B Protocols
Schneider Electric Buildings AB, June 2011 179 (184)
04-00124-06-en
allow group control to be cooperatively shared with other control
devices.
• Group Ramp Rate – Optional parameter that is normally left
blank or set to Instant to cause lighting state changes to occur
immediately. However, if dimming is available then some other
rate may be selected to cause the light level to ramp gradually if
preferred. The C-Bus allows the ramp rate to be achieved with a
single message, so there is no overhead when electing not to
switch instantly.
• I/O Signal Direction – Most C-Bus Group Variable signals are
used to control a lighting group’s level, in which case the I/O col-
umn parameter should be set to Write-only (W). Where it is neces-
sary to monitor the state of a group variable the I/O direction
should be set to Read-only (R).
• Coefficient Gain and Offset – The conversion coefficient gain is
automatically set based on the group variable type selection. The
gain is 1 for every ON/OFF, ON Only or OFF Only type, or
100/255 for every LEVEL type so that the C-Bus level is
expressed as a percentage between 0 and 100.
• Signal DataType – The signal data type is automatically set based
on the group variable type selection. Each ON/OFF, ON Only or
OFF Only value is a 2-state BOOL, whereas each LEVEL value
is expressed as a REAL percentage number.
• Signal Measurement System – The measurement system units
are automatically set based on the group variable type selection.
Each ON/OFF, ON Only or OFF Only is an ON/OFF enumera-
tion, whereas each LEVEL type has percentage units (%).
B.8.5 Multiple Write-Only Signals Per Group Variable
Normally only one write-only signal is used to control a Group Vari-
able. However, with care, multiple signals can share control if required.
This is because a group control message is only sent onto the C-Bus net-
work when an signal changes state, so conflicting control requests do
not cause problems if the state changes occur at sufficiently separate
times.
As an example, it could be useful to have 2 write-only signals control-
ling one group so that a warning of shutdown could be issued. In this
case, one signal could request a ramp down to a 50% lighting level 5
minutes before a 2nd signal turned off the lights completely.
Note
• ON Only and OFF Only types are NOT applicable to read-only
values.