Rockwell Automation 1756-IH16ISOE ControlLogix Sequence of Events Module - Manual (Page 92)

Publication 1756-UM528A-EN-P - April 2004
7-6 Using The Sequence of Events Module in FIFO Mode
Using Latch CST in FIFO Mode
When enabled, Latch CST prevents the Sequence of Events module
from overwriting input data once it is timestamped. This feature is
set on a module-wide basis and is enabled by default.
Table 7.2 describes how Latch CST affects the module in FIFO mode.
Table 7.2
If Latch CST is
the following occurs
(1)
:
Enabled The Sequence of Events module timestamps input transitions as they occur, and stores the data for those
transitions in its on-board buffer. If you fail to empty the buffer (as described on page 7-10) faster than it is filled,
after 160 timestamped input transitions, the module ignores additional transitions.
Once the Sequence of Events module buffer is filled, the next input transition is not timestamped and the
I.EventOverflow for the point where the transition occurred is set to one to inform the controller that events
occurred but were not timestamped.
0 1 1 0 0 1 0
1 1 0 0 1 1 0
0 1 0 0 0 1 0
1 1 0 0 1 1 0
1 0 1 0 0 1 0
1 1 0 0 1 1 0
1 0 1 0 0 1 1
0 0 0 0 1 1 0
1 1 0 0 1 0 1
1 0 0 1 1 1 0
1 1 1 0 0 1 1
0 1 1 0 0 1 0
1 1 0 0 1 1 0
0 1 0 0 0 1 0
1 1 0 0 1 1 0
1 0 1 0 0 1 0
1 1 0 0 1 1 0
1 0 1 0 0 1 1
0 0 0 0 1 1 0
1 1 0 0 1 0 1
1 0 0 1 1 1 0
1 1 1 0 0 1 1
1
2
3
4
5
6
7
8
9
159
160
1
2
3
4
5
6
7
8
9
159
160
4
2
8
11
9
1
2
7
10
12
5
4
2
8
11
9
1
2
7
10
12
5
0
1
1
0
0
0
1
1
0
0
1
0
1
1
0
0
0
1
1
0
0
1
The Sequence of Events
module has timestamped and
recorded enough input
transitions since the controller
last retrieved data, that the
on-board buffer is full.
Input 3 transitions for OFF to ON.
Because Latch CST is enabled
and the Sequence of Events
module’s on-board buffer is full, it
does not timestamp the
transition.
All data in the buffer remains the
same, and the module increments
the I.EventOverflow tag.
The data in the
buffer here matches
the data in the
buffer above.
Timestamp data #1
Timestamp data #160
43806
Timestamp Event # Input # Input State
Timestamp Event # Input # Input State