Rockwell Automation 1756-IH16ISOE ControlLogix Sequence of Events Module - Manual (Page 78)

Publication 1756-UM528A-EN-P - April 2004
6-6 Using The Sequence of Events Module in CST Per Point Mode
Using Latch CST in CST Per Point Mode
When enabled, Latch CST prevents the Sequence of Events module
from overwriting recorded timestamp data once a transition occurs.
This feature is set on a module-wide basis and is enabled by
default. Table 6.2 describes how Latch CST affects the module in CST
Per Point mode.
Use the Configuration tab in RSLogix 5000 to enable Latch CST, as
shown in the example below.
Table 6.2
If Latch CST is the following occurs (1)
:
Enabled The Sequence of Events module timestamps two transitions for each input–one for OFF to ON and one for ON to OFF. If
similar transitions occur on inputs where a transition has already been timestamped and the data was not yet
acknowledged (for more information on acknowledging data, see page 6-12), the module does not timestamp the new
transition.
When transitions occur that the Sequence of Events module does not timestamp, the module sets the I.EventOverflow
tag for that point to inform the controller that an input transitioned but a timestamp was not produced for the transition.
Typically, Latch CST is enabled in CST Per Point mode.
Disabled The Sequence of Events module timestamps each transition for each input as it occurs. In this case, when multiple
transitions occur in the same direction on the same input, the module records the new timestamp data, overwriting any
previously-recorded data which had yet to be acknowledged (for more information on acknowledging data, see
page 6-12).
When the Sequence of Events module overwrites data, it sets the I.EventOverflow tag for that point to inform the
controller that events have been overwritten.
(1) This table assumes the transition occurs on inputs that have Enable CST Capture enabled. If Enable CST Capture is disabled, the module does not timestamp transitions on
that input and, therefore, Latch CST does not affect module behavior.
IMPORTANT
We suggest you monitor the I.EventOverflow bits to
make sure you are aware of when transitions were
either not timestamped or when timestamp data
was overwritten.
Click this box to enable the
Latch CST feature.
Clear the box to disable
the feature.