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Chapter 10
Use the Sequence of Events Input and Scheduled Output Modules
64
Use the Sequence of Events Module in FIFO Mode
In First In First Out (FIFO) mode, the Sequence of Events module timestamps
multiple input transitions on any CIP Sync/PTP Capture-enabled inputs. The
module stores the timestamp data in on-board buffers that hold 256
timestamp events per channel. Each of the 8 inputs has its own buffer.
When an input transitions, the module timestamps the event and records
specific input data related to the transition. The owner-controller must
retrieve the data from the Sequence of Events module using one of the two
methods described later in this chapter.
IMPORTANT Keep in mind that, although the Sequence of Events module can store up to
256 events per input, if you manage the buffer effectively (that is, retrieve
data in a timely fashion), the module can timestamp an infinite number of
input transitions and the controller will be able to retrieve and use the data.
How Does the On-Board Buffer Work in FIFO Mode?
The module stores up to 256 events per input. Once data is stored on the
module, the controller must retrieve it. Typically, the controller retrieves data
from the first slot in the on-board buffer; the data in the first slot is also known
as the current event.
IMPORTANT The current event is the event for which the Sequence of Events module is
currently producing data. The current event is NOT the most recently-
timestamped input transition.
After the controller retrieves the current event data, it acknowledges the data
and clears it from the Sequence of Events module's on-board buffers, and the
data from the next slot in the buffer becomes the current event (that is, the
module produces this data for the controller).
In FIFO mode, generally the following occurs:
1. You configure the Sequence of Events module to operate in FIFO mode
via the Communication Format selection.
2. The Sequence of Events module timestamps each transition and stores
the data in its on-board buffer. The module can timestamp each
transition with a unique CIP Sync/PTP as long as the transitions occur 25
μs apart.
3. The controller retrieves data from the Sequence of Events module as
described in the following steps:
a. Immediately after the Sequence of Events module timestamps an
input transition, it records data in the first slot of its on-board buffer
and produces the data for the controller; the data is the current event.
The module produces the data from the current event at every
subsequent RPI until the controller clears it (as described in step C).
b. The controller copies the data from the controller tags to a separate
data structure for later use.
c. The controller acknowledges the current event in the Sequence of
Events module's buffer by I.EventNumber to O.EventNumber.
Rockwell Automation Publication 1732E-UM003D-EN-E - November 2021
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