Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
Supercedes Publication 1756-PM005J-EN-P - March 2022
Programming Manual
Original Instructions
Logix 5000 Controllers
Tasks, Programs, and
Routines
1756 ControlLogix, 1756 GuardLogix, 1769 CompactLogix,
1769 Compact GuardLogix, 1789 SoftLogix, 5069
CompactLogix, 5069 Compact GuardLogix, Studio 5000
Logix Emulate
Logix 5000 Controllers Tasks, Programs, and Routines
2 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
Important User Information
Read this document and the documents listed in the additional resources section about installation, configuration, and
operation of this equipment before you install, configure, operate, or maintain this product. Users are required to familiarize
themselves with installation and wiring instructions in addition to requirements of all applicable codes, laws, and standards.
Activities including installation, adjustments, putting into service, use, assembly, disassembly, and maintenance are required to
be carried out by suitably trained personnel in accordance with applicable code of practice.
If this equipment is used in a manner not specified by the manufacturer, the protection provided by the equipment may be
impaired.
In no event will Rockwell Automation, Inc. be responsible or liable for indirect or consequential damages resulting from the use
or application of this equipment.
The examples and diagrams in this manual are included solely for illustrative purposes. Because of the many variables and
requirements associated with any particular installation, Rockwell Automation, Inc. cannot assume responsibility or liability for
actual use based on the examples and diagrams.
No patent liability is assumed by Rockwell Automation, Inc. with respect to use of information, circuits, equipment, or software
described in this manual.
Reproduction of the contents of this manual, in whole or in part, without written permission of Rockwell Automation, Inc., is
prohibited.
Throughout this manual, when necessary, we use notes to make you aware of safety considerations.
WARNING:
Identifies information about practices or circumstances that can cause an explosion in a hazardous environment, which may lead to
personal injury or death, property damage, or economic loss.
ATTENTION:
Identifies information about practices or circumstances that can lead to personal injury or death, property damage, or economic loss.
Attentions help you identify a hazard, avoid a hazard, and recognize the consequence.
IMPORTANT
Identifies information that is critical for successful application and understanding of the product.
Labels may also be on or inside the equipment to provide specific precautions.
SHOCK HAZARD:
Labels may be on or inside the equipment, for example, a drive or motor, to alert people that dangerous voltage may be present.
BURN HAZARD:
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temperatures.
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cause severe injury or death. Wear proper Personal Protective Equipment (PPE). Follow ALL Regulatory requirements for safe work practices and for
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Rockwell Automation recognizes that some of the terms that are currently used in our industry and in this publication are not in
alignment with the movement toward inclusive language in technology. We are proactively collaborating with industry peers to
find alternatives to such terms and making changes to our products and content. Please excuse the use of such terms in our
content while we implement these changes.
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 3
Summary of changes
This manual includes new and updated information. Use these reference
tables to locate changed information.
Grammatical and editorial style changes are not included in this summary.
Global changes
This table identifies changes that apply to all information about a subject in
the manual and the reason for the change. For example, the addition of new
supported hardware, a software design change, or additional reference
material would result in changes to all the topics that deal with that subject.
Change
Topic
Added inclusive language notice
Preface on page 7
New or enhanced features
None in this release.
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 5
Table of Contents
Studio 5000 environment ........................................................................... 7
Additional resources .................................................................................... 8
Legal Notices ................................................................................................ 8
Chapter 1
Introduction ................................................................................................. 9
Select Controller Tasks ................................................................................ 9
Use Caution in the Number of Tasks That You Use .......................... 11
Prioritize Periodic and Event tasks ........................................................... 11
Additional Considerations .................................................................. 12
Example ................................................................................................ 12
Leave Enough Time for Unscheduled Communication .......................... 13
Avoid Overlaps ............................................................................................ 14
Manually Check for Overlaps .............................................................. 15
Programmatically Check for Overlaps................................................ 16
Configure Output Processing for a Task .................................................. 17
Manually Configure Output Processing............................................ 20
Programmatically Configure Output Processing .............................. 21
Inhibit a Task .............................................................................................. 21
Manually Inhibit or Uninhibit a Task ................................................ 22
Programmatically Inhibit or Uninhibit a Task ..................................23
Create a Task .............................................................................................. 24
Create a Periodic Task ........................................................................ 25
Language Switching ........................................................................... 27
Adjust the System-overhead Time Slice .................................................. 27
Configure the System-overhead Time Slice ...................................... 29
Adjust the System Watchdog Time .......................................................... 30
Adjust the Watchdog Timer for a Task .............................................. 30
Chapter 2
Introduction ............................................................................................... 33
Choose the trigger for an event task ........................................................ 33
Module Input Data State Change Trigger ................................................ 35
How an I/O Module Triggers an Event Task ...................................... 36
Make Sure Your Module Can Trigger an Event Task ........................ 37
Checklist for an Input Event Task ..................................................... 38
Example – Input Event Task................................................................ 39
Estimate Throughput.......................................................................... 40
Example - Estimate Throughput........................................................ 42
Additional Considerations .................................................................. 43
Motion Group Trigger ................................................................................ 43
Summary of changes
Preface
Manage Tasks
Manage Event Tasks
Table of Contents
6 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
Checklist for a Motion Group Task .................................................... 44
Axis Registration Trigger ...........................................................................45
Checklist for an Axis Registration Task............................................. 46
Example - Axis Registration Trigger .................................................. 47
Axis Watch Trigger .................................................................................... 49
Checklist for an Axis Watch Task....................................................... 50
Example - Axis Watch Trigger............................................................ 50
Consumed Tag Trigger .............................................................................. 53
Maintain the Integrity of Data ............................................................ 55
Synchronize multiple controllers ....................................................... 55
Checklist for the Producer Controller ................................................ 57
Checklist for the Consumer Controller ............................................. 58
Example - Producer Controller and Consumer Controller .............. 58
EVENT Instruction Trigger ...................................................................... 60
Programmatically Determine if EVENT Instruction Triggered Task
............................................................................................................... 61
Checklist for an EVENT Instruction Task ......................................... 62
Example – EVENT Instruction Trigger ............................................. 62
Define a Timeout Value for an Event Task ............................................... 63
Assign a Timeout Value to an Event Task .......................................... 63
Programmatically Configure a Timeout ........................................... 64
Programmatically determine if a timeout occurs .............................65
Index
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 7
Preface
This manual is one of a set of related manuals that show common procedures
for programming and operating Logix 5000 controllers.
For a complete list of common procedures manuals, refer to the Logix 5000
Controllers Common Procedures Programming Manual, publication
1756-PM001.
The term Logix 5000 controller refers to any controller based on the Logix
5000 operating system.
Rockwell Automation recognizes that some of the terms that are currently
used in our industry and in this publication are not in alignment with the
movement toward inclusive language in technology. We are proactively
collaborating with industry peers to find alternatives to such terms and
making changes to our products and content. Please excuse the use of such
terms in our content while we implement these changes.
The Studio 5000 Automation Engineering & Design Environment® combines
engineering and design elements into a common environment. The first
element is the Studio 5000 Logix Designer® application. The Logix Designer
application is the rebranding of RSLogix 5000® software and will continue to
be the product to program Logix 5000™ controllers for discrete, process,
batch, motion, safety, and drive-based solutions.
The Studio 5000® environment is the foundation for the future of
Rockwell Automation® engineering design tools and capabilities. The Studio
5000 environment is the one place for design engineers to develop all
elements of their control system.
Studio 5000 environment
Preface
8 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
These documents contain additional information concerning related
Rockwell Automation products.
Resource
Description
Industrial Automation Wiring and Grounding
Guidelines, publication 1770-4.1
Provides general guidelines for installing a Rockwell
Automation industrial system.
Product Certifications webpage, available at
http://ab.rockwellautomation.com
Provides declarations of conformity, certificates, and
other certification details.
View or download publications at
http://www.rockwellautomation.com/literature. To order paper copies of
technical documentation, contact the local Rockwell Automation distributor
or sales representative.
Rockwell Automation publishes legal notices, such as privacy policies, license
agreements, trademark disclosures, and other terms and conditions on the
Legal Notices page of the Rockwell Automation website.
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You can view the Rockwell Automation End-User License Agreement ("EULA")
by opening the License.rtf file located in your product's install folder on your
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licensed under one or more open source licenses. Copies of those licenses are
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Alternately, obtain complete Corresponding Source code by contacting
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Please include "Open Source" as part of the request text.
A full list of all open source software used in this product and their
corresponding licenses can be found in the OPENSOURCE folder. The default
installed location of these licenses is
C:\Program Files (x86)\Common
Files\Rockwell\Help\<Product Name>\Release
Notes\OPENSOURCE\index.htm
.
Additional resources
Legal Notices
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 9
Chapter 1
Manage Tasks
The default project provides one task for all your logic. Although this is
sufficient for many applications, some situations may require multiple tasks.
A Logix 5000 controller supports multiple tasks to schedule and prioritize the
running of your programs based on specific criteria. This balances the
processing time of the controller.
• The controller runs only one task at one time.
• Another task can interrupt a task that is running and take control.
• In any given task, only one program runs at one time.
A Logix 5000 controller supports the following types of tasks.
If you want to run a section
of your logic
Then use this
type of task
Description
All the time Continuous Task The continuous task runs in the background. Any CPU time not allocated to other
operations (such as motion, communication, and periodic or event tasks) is used to
run the programs within the continuous task.
• The continuous task runs all the time. When the continuous task completes a full
scan, it restarts immediately.
• A project does not require a continuous task. If used, there can be only one
continuous task.
• At a constant period (for
example, every 100 ms)
• Multiple times within the scan
of your other logic
Periodic Task A periodic task performs a function at a specific period. When the time for the
periodic task expires, the periodic task:
• Interrupts any lower priority tasks.
• Runs one time.
• Returns control to where the previous task left off.
You can configure the time period from 0.1 ms…2000 s. The default is 10 ms.
Immediately when an event
occurs
Event Task An event task performs a function only when a specific event (trigger) occurs.
When the trigger for the event task occurs, the event task:
• Interrupts any lower priority tasks.
• Runs one time.
• Returns control to where the previous task left off.
The trigger can be a:
• Change of a digital input.
• New sample of analog data.
• Certain motion operations.
• Consumed tag.
• EVENT instruction.
Important: Some Logix 5000 controllers do not support all triggers.
Introduction
Select Controller Tasks
Chapter 1 Manage Tasks
10 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
The following table lists example situations for the tasks.
For this example situation
Use this type of task
Fill a tank to its maximum level and then open a drain valve. Continuous task
Collect and process system parameters and send them to a display.
Continuous task
Complete step 3 in a control sequence—reposition the bin diverter.
Continuous task
Your system must check the position of a field arm each 0.1 s and calculate the average
rate of change in its position. This is used to determine braking pressure.
Periodic task
Read the thickness of a paper roll every 20 ms. Periodic task
A packaging line glues boxes closed. When a box arrives at the gluing position, the
controller must immediately run the gluing routine.
Event task
In a high-speed assembly operation, an optical sensor detects a certain type of reject.
When the sensor detects a reject, the machine must immediately divert the reject.
Event task
In an engine test stand, you want to capture and archive each analog data immediately
after each sample of data.
Event task
Immediately after receiving new production data, load the data into the station.
Event task
In a line that packages candy bars, you have to make sure that the perforation occurs in
the correct location on each bar. Each time the registration sensor detects the
registration mark, check the accuracy of an axis and perform any required adjustment.
Event task
A gluing station must adjust the amount of glue it applies to compensate for changes in
the speed of the axis. After the motion planner runs, check the command speed of the
axis and vary the amount of glue, if needed.
Event task
In a production line, if any of the programs detect an unsafe condition the entire line
must shut down. The shutdown procedure is the same regardless of the unsafe
condition.
Event task
The number of tasks supported depends on the controller.
This controller
Supports this number of
tasks
Notes
ControlLogix
1756-L71
1756-L72
1756-L73
1756-L74
1756-L75
GuardLogix
1756-L71S
1756-L72S
1756-L73S
SoftLogix5800
1756-L7SP
32
32
32
Only one task can be
continuous.
Chapter 1 Manage Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 11
This controller
Supports this number of
tasks
Notes
CompactLogix
1769-L2x
1769-L31
1769-L32x
1769-L35x
1768-L43
1768-L45
1769-L16x
1769-L18x
1769-L19x
1769-L24x
1769-L27x
1769-L30x
1769-L33x
1769-L36x
1769-L37x
3
4
6
8
16
32
Typically, each task takes controller time away from the other tasks. If you
have too many tasks, then:
• The continuous task may take too long to complete.
• Another task may overlap. If a task is interrupted too frequently or too
long, it may not finish running before it is triggered again.
Although a project can contain multiple tasks, the controller runs only one
task at a time. If a periodic or event task is triggered while another task is
running, the priority of each task indicates what the controller should do.
The number of priority levels depends on the controller.
This Logix 5000 controller
Has this many priority levels
CompactLogix 15
ControlLogix
15
DriveLogix
15
FlexLogix
15
SoftLogix5800
3
To assign a priority to a task, use the following guidelines.
If you want
Then
Notes
This task to interrupt
another task
Assign a priority number that is less than
(higher priority) the priority number of the
other task.
• A higher priority task interrupts all
lower priority tasks.
• A higher priority task can
interrupt a lower priority task
multiple times.
Another task to interrupt
this task
Assign a priority number that is greater than
(lower priority) the priority number of the
other task.
This task to share
controller time with
another task
Assign the same priority number to both
tasks.
The controller switches back and
forth between each task and runs
each task for 1 ms.
Use Caution in the Number
of Tasks That You Use
Prioritize Periodic and
Event tasks
Chapter 1 Manage Tasks
12 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
As you estimate the execution interrupts for a task, consider the following.
Consideration
Description
Motion planner
The motion planner interrupts all user tasks, regardless of their priority.
• The number of axes and coarse update period for the motion group affect how long
and how often the motion planner runs.
• If the motion planner is running when a task is triggered, the task waits until the
motion planner is done.
• If the coarse update period occurs while a task is running, the task pauses to let the
motion planner run.
I/O task
Tip:
CompactLogix controllers do not have I/O tasks.
FlexLogix, and DriveLogix controllers use a dedicated periodic task to process I/O data.
This I/O task:
• Does not show up in the Tasks folder of the controller.
• Does not count toward the task limits for the controller.
• Operates at priority 6.
• Runs at the fastest RPI you have scheduled for the system.
• Runs for as long as it takes to scan the configured I/O modules.
As you assign priorities to your tasks, consider the I/O task.
If you want a task to
Then assign one of these priorities
Interrupt or delay I/O processing 1…5
Share controller time with I/O processing 6
Let I/O processing interrupt or delay the
task
7…15
System overhead System overhead is the time that the controller spends on unscheduled communication.
• Unscheduled communication is any communication that you do not configure
through the I/O configuration folder of the project, such as Message (MSG)
instructions and communication with HMIs or workstations.
• System overhead interrupts only the continuous task.
• The system overhead time slice specifies the percentage of time (excluding the time
for periodic or event tasks) that the controller devotes to unscheduled
communication.
• The controller performs unscheduled communication for up to 1 ms at a time and
then resumes the continuous task.
Continuous task You do not assign a priority to the continuous task. It always runs at the lowest priority.
All other tasks interrupt the continuous task.
The following example shows the execution of a project with three user tasks.
Task
Priority
Period
Execution time
Duration
Motion planner N/A 8 ms (base update
rate)
1 ms 1 ms
Event task 1
1
N/A
1 ms
1…2 ms
Periodic task 1
2
12 ms
2 ms
2…4 ms
I/O task—n/a to CompactLogix,
ControlLogix and SoftLogix
controllers. See
Additional
Considerations
.
7 5 ms (fastest RPI) 1 ms 1…5 ms
System overhead N/A Time slice = 20% 1 ms 1…6 ms
Continuous task
N/A
N/A
20 ms
48 ms
Additional Considerations
Example
Chapter 1 Manage Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 13
Description
Initially, the controller runs the motion planner and the I/O task (if one exists).
After running the continuous task for 4 ms, the controller triggers the system overhead.
The period for periodic task 1 expires (12 ms), so the task interrupts the continuous task.
After running the continuous task again for 4 ms, the controller triggers the system overhead.
The trigger occurs for event task 1.
Event task 1 waits until the motion planner is done.
Lower priority tasks are delayed.
The continuous task automatically restarts.
The Studio 5000 environment includes a task monitor tool on the distribution
CD. You can use this tool to analyze how tasks are running.
See also
Additional Considerations on page 12
Unscheduled communication occurs only when a periodic or event task is not
running. If you use multiple tasks, make sure that the scan times and
execution intervals leave enough time for unscheduled communication. Use
the following methods to plan enough unscheduled communication time.
1. Verify that the execution time of a highest priority task is significantly
less than its specified period.
Leave Enough Time for
Unscheduled
Communication
Chapter 1 Manage Tasks
14 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
2. Verify that the total execution time of all your tasks is significantly less
than the period of the lowest priority tasks.
For example, the following is true in this configuration.
Task
Priority
Execution Time
Period Specified
1 Higher 20 ms 80 ms
2
Lower
30 ms
100 ms
Total execution time: 50 ms
• The execution time of the highest priority task (Task 1) is significantly
less than its specified period (20 ms is less than 80 ms).
• The total execution time of all tasks is significantly less than the
specified period of the lowest priority task (50 ms is less than 100 ms).
The following guidelines generally leave enough time for unscheduled
communication.
• Adjust the period of the tasks as needed to get the best balance
between running your logic and servicing unscheduled
communication.
• If your project has a continuous task, unscheduled communication
occurs as a percentage of controller time (excluding the time for
periodic or event tasks).
An overlap is a condition where a task (periodic or event) is triggered while
the task is still running from the previous trigger.
IMPORTANT
If an overlap occurs, the controller disregards the trigger that caused the overlap. In
other words, you might miss an important execution of the task.
Description
Task trigger occurs.
Task runs.
Task trigger occurs.
Task runs.
Task trigger occurs.
Task runs.
Avoid Overlaps
Chapter 1 Manage Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 15
Description
Overlap occurs. Task is triggered while it is still running.
The trigger does not restart the task. The trigger is ignored.
Each task requires enough time to finish before it is triggered again. Make
sure that the scan time of the task is significantly less than the rate at which
the trigger occurs. If an overlap occurs, reduce the frequency at which you
trigger the task.
If the type of task is
Then
Periodic Increase the period of the task.
Event Adjust the configuration of your system to trigger the task less
frequently.
Follow these steps to manually see if overlaps are occurring for a task.
To manually check for overlaps
1. In the Controller Organizer, right-click MainTask and choose
Properties.
Manually Check for
Overlaps
Chapter 1 Manage Tasks
16 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
2. On the Task Properties dialog box, select the Monitor tab.
The Task Overlap Count shows the number of overlaps since the
counter was last reset.
3. Select OK.
See also
Manually Configure Output Processing on page 19
Manually Inhibit or Uninhibit a Task on page 22
When an overlap occurs, the controller:
• Logs a minor fault to the FAULTLOG object.
• Stores overlap information in the Task object for the task.
To write logic to check for an overlap, use a Get System Value (GSV)
instruction to monitor either of these objects.
If you want to
Then access the object and attribute
Object
Attribute
Data Type
Description
Determine if an overlap occurred for any
task
FaultLog MinorFaultBits DINT Individual bits that indicate a minor fault:
To determine if
Examine this bit
An instruction produced a minor fault. 4
An overlap occurred for a task. 6
The serial port produced a minor fault. 9
The battery/ESM is not present or needs
replacement.(1)
10
Programmatically Check
for Overlaps
Chapter 1 Manage Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 17
If you want to
Then access the object and attribute
Object
Attribute
Data Type
Description
Determine if an overlap occurred for a
specific task
Task Status DINT Status information about the task. Once the controller sets one of
these bits, you must manually clear the bit.
To determine if
Examine this bit
An EVENT instruction triggered the task
(event task only).
0
A timeout triggered the task (event task
only).
1
An overlap occurred for this task. 2
Determine the number of times that an
overlap occurred.
Task OverlapCount DINT Valid for an event or a periodic task.
To clear the count, set the attribute to 0.
1. Battery for 1756-L6X, 1769-L2X, and 1769-L3X controllers. ESM for 1756-L7X and CompactLogix 5370 series controllers.
Example
1. The GSV instruction sets Task_2_Status = Status attribute for Task_2
(DINT value).
2. If Task_2_Status.2 = 1, then an overlap occurred, so get the count of
overlaps:
The GSV instruction sets Task_2_Overlap_Count (DINT tag) =
OverlapCount attribute of Task_2.
3. If Condition_1 = 1, then clear the bits of the Status attribute for Task_2:
The SSV instruction sets the Status attribute of Task_2 = Zero. Zero is a
DINT tag with a value of 0.
At the end of a task, the controller performs overhead operations (output
processing) for the I/O modules in your system. Although these operations
are not the same as updating the modules, the output processing may affect
the update of the I/O modules in your system.
Configure Output
Processing for a Task
Chapter 1 Manage Tasks
18 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
As an option, you can turn off this output processing for a specific task, which
reduces the elapsed time of that task.
Select Disable Automatic Output Processing To Reduce Task Overhead to
disable the processing of outputs at the end of the task.
Chapter 1 Manage Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 19
Choose how to configure output processing for a task.
Chapter 1 Manage Tasks
20 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
Follow these steps to manually configure output processing.
1. In the Controller Organizer, right-click MainTask and choose
Properties.
2. On the Task Properties dialog box, click the Configuration tab.
3. Configure output processing for the task.
If you want to
Then
Enable the processing of outputs at
the end of the task
Clear
Disable Automatic Output Processing To Reduce
Task Overhead (default).
Disable the processing of outputs at
the end of the task
Check
Disable Automatic Output Processing To Reduce
Task Overhead.
4. Click OK.
Manually Configure
Output Processing
Chapter 1 Manage Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 21
To write logic to configure output processing for a task, use a
Set System Value (SSV) instruction. Access the attribute of the Task object for
the task.
If You Want to
Access This Attribute
Data Type
Instruction
Description
Enable or disable the
processing of outputs at the
end of a task
DisableUpdateOutputs
DINT
GSV
SSV
To
Set the attribute to
Enable the processing
of outputs at the end of
the task
0
Disable the processing
of outputs at the end of
the task
1 (or any non-zero value)
Example
If Condition_1 = 0 then let Task_2 process outputs when it is done.
1. The ONS instruction limits the true run of the SSV instruction to one
scan.
2. The SSV instruction sets the DisableUpdateOutputs attribute of
Task_2 = 0. This lets the task automatically process outputs when it
finishes its run.
If Condition_1 = 1 then do not let Task_2 process outputs when it is done.
1. The ONS instruction limits the true run of the SSV instruction to one
scan.
2. The SSV instruction sets the DisableUpdateOutputs attribute of
Task_2 = 1. This prevents the task from automatically processing
outputs when it finishes its run.
By default, each task runs based on its trigger (event, periodic, or
continuous). As an option, you can prevent a task from running when its
trigger occurs (that is, inhibit the task). This is useful when you test, diagnose,
or start up your project.
Programmatically Configure
Output Processing
Inhibit a Task
Chapter 1 Manage Tasks
22 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
If You Want to
Then
Let the task run when its trigger occurs
Uninhibit the task (default).
Prevent the task from running when its trigger
occurs
Inhibit the task.
EXAMPLE
During the commissioning of a system that uses several tasks, you can first test each task
individually.
• Inhibit all the tasks except one, and then test that task.
• Once the task meets your requirements, inhibit it and uninhibit a different task.
Continue this process until you have tested all your tasks.
If a task is inhibited, the controller still prescans the task when the controller
transitions from Program to Run or Test mode.
Follow these steps to manually inhibit or uninhibit the running of a task.
1. In the Controller Organizer, right-click MainTask and choose
Properties.
Manually Inhibit or
Uninhibit a Task
Chapter 1 Manage Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 23
2. On the Task Properties dialog box, click the Configuration tab.
3. Do one of these steps to inhibit or uninhibit the task.
If You Want to
Then
Let the task run when its trigger occurs Clear
Inhibit Task
(default).
Prevent the task from running when its trigger
occurs
Check
Inhibit Task
.
4. Click OK.
To write logic to inhibit or uninhibit a task, use a Set System Value (SSV)
instruction to access the attribute of the Task object for the task.
Attribute
Data Type
Instruction
Description
InhibitTask
DINT
GSV
SSV
Prevents the task from running.
To
Set the attribute to
Enable the task 0 (default)
Inhibit (disable) the task
1 (or any non-zero value)
Example
If Condition_1 = 0 then let Task_2 run.
1. The ONS instruction limits the true run of the SSV instruction to one
scan.
2. The SSV instruction sets the InhibitTask attribute of Task_2 = 0. This
uninhibits the task.
Programmatically Inhibit or
Uninhibit a Task
Chapter 1 Manage Tasks
24 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
If Condition_1 = 1 then do not let Task_2 run.
1. The ONS instruction limits the true run of the SSV instruction to one
scan.
2. The SSV instruction sets the InhibitTask attribute of Task_2 = 1. This
inhibits the task.
Follow these steps to create an event task.
1. In the Controller Organizer, right-click the Tasks folder and choose
New Task.
Create a Task
Chapter 1 Manage Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 25
2. Enter task information in the New Task dialog box.
Topic
Description
Name Type a name for the task.
Description Type an optional description for the task.
Type
Choose Event for the task type.
Trigger
Choose a trigger for the task.
Tag Choose a tag if the field is active for the selected trigger.
Execute Task If No Event Occurs Within Check the box and type a time period that must elapse
before a task can run.
Priority Enter the task priority value.
Watchdog
Type the watchdog time for the task.
3. Click OK.
A periodic task performs a function or functions at a specific rate.
IMPORTANT
Be sure that the time period is longer than the sum of the run times of all the programs
assigned to the task.
• If the controller detects that a periodic task trigger occurs for a task that is already
operating, a minor fault occurs (overlap).
• Priorities and run times of other tasks may also cause an overlap.
Create a Periodic Task
Chapter 1 Manage Tasks
26 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
1. In the Controller Organizer, right-click the MainTask folder and
choose Properties.
2. On the Task Properties dialog box, click the Configuration tab.
Chapter 1 Manage Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 27
3. Enter this information in the Task Properties dialog box.
Topic
Description
Type Choose
Periodic
(default) for the type of task.
Period Type a value for when (or at what time interval) you
want the task to run.
Priority
Enter the task priority value.
Watchdog
Type the watchdog time for the task.
4. Click OK.
In versions 17 and later of the application, you can display project
documentation, such as tag descriptions and rung comments, for any
supported localized language. You can store project documentation for
multiple languages in a single project file rather than in language-specific
project files. You define all the localized languages that the project will
support and set the current, default, and optional custom-localized language.
The software uses the default language if the current language's content is
blank for a particular component of the project. However, you can use a
custom language to tailor documentation to a specific type of project file user.
Enter the localized descriptions in your project, either when programming in
that language or by using the import/export utility to translate the
documentation offline and then import it back into the project. When you
enable language switching, you can dynamically switch between languages as
you use the software.
Project documentation that supports multiple translations within a project
includes the following:
• Component descriptions in tags, routines, programs, user-defined
data types, and Add-On Instructions
• Equipment phases
• Trends
• Controllers
• Alarm Messages (in ALARM_ANALOG and ALARM_DIGITAL
configuration)
• Tasks
• Property descriptions for modules in the Controller Organizer
• Rung comments, SFC text boxes, and FBD text boxes
A Logix 5000 controller communicates with other devices, I/O modules,
controllers, HMI terminals, and so forth, at either a specified rate (scheduled)
or when there is processing time available to service the communication
(unscheduled).
This type of communication
Is
Update I/O data (not including block-transfers)
Scheduled
Communication
Produce or consume tags
Communicate with programming devices (that is, the Logix Designer application)
Service
Communication
Communicate with HMI devices
Run Message (MSG) instructions, including block-transfers
Language Switching
Adjust the
System-overhead
Time Slice
Chapter 1 Manage Tasks
28 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
This type of communication
Is
Respond to messages from other controllers
Synchronize the secondary controller of a redundant system
Re-establish and monitor I/O connections (such as Removal and Insertion Under
Power conditions); this does not include normal I/O updates that occur during the
running of logic
Service communication is any communication that you do not configure
through the I/O configuration folder of the project.
The system-overhead time slice specifies the percentage of time a controller
devotes to service communication. However, if there is no continuous task,
the overhead time slice has no effect. If you have both a periodic and a
continuous task, the value selected on the Advanced tab of the Controller
Properties dialog box determines the ratio of running the continuous task
and service communication.
The following table shows the ratio between the continuous task and service
communication at various system overhead time slices.
At this time slice
The continuous tasks runs
Service communication occurs for up
to
10%
9 ms
1 ms
20%
4 ms
1 ms
25%
3 ms
1 ms
33%
2 ms
1 ms
50% 1 ms 1 ms
66% 1 ms 2 ms
75% 1 ms 3 ms
80% 1 ms 4 ms
90%
1 ms
9 ms
As shown in the table, for version 16 and later of the application, the system
overhead time slice at 50% stays fixed at 1 ms.
The same applies for 66% and higher, except that there are multiple 1 ms
intervals. For example, at 66% there are two 1 ms intervals of consecutive time
and at 90% there are nine 1 ms intervals of consecutive time.
Chapter 1 Manage Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 29
Follow these steps to configure the system-overhead time slice.
To configure the system-overhead time slice
1. On the Online toolbar, select the controller properties icon.
2. On the Controller Properties dialog box, select the Advanced tab.
3. Enter a number in the System Overhead Time Slice box.
4. Use either Run Continuous Task (default) or Reserve for System
Tasks.
• Select the Run Continuous Task radio button when there are no
communication or background tasks to process; the controller
immediately returns to the continuous task.
• Select the Reserve for System Task radio button to allocate the
entire 1 ms of the system-overhead time slice when the controller
has communication or background tasks to perform before
returning to the continuous task. This lets you simulate a
communication load on the controller during design and
Configure the
System-overhead
Time Slice
Chapter 1 Manage Tasks
30 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
programming before HMIs, controller to controller messaging, and
so forth, are set up. Use this setting for testing purposes only.
5. Select OK.
Each task contains a watchdog timer that specifies how long a task can run
before triggering a major fault.
ATTENTION:
If the watchdog timer reaches a configurable preset, a major fault occurs.
Depending on the controller fault handler, the controller might shut down.
• A watchdog time can range from 1…2,000,000 ms (2000 seconds). The
default is 500 ms.
• The watchdog timer begins to run when the task is initiated and stops
when all the programs within the task have run.
• If the task takes longer than the watchdog time, a major fault occurs.
(The time includes interruptions by other tasks.)
• You can use the controller fault handler to clear a watchdog fault. If the
same watchdog fault occurs a second time during the same logic scan,
the controller enters Faulted mode, regardless of whether the
controller fault handler clears the watchdog fault.
Follow these steps to change the watchdog time of a task.
To adjust the watchdog timer for a task
1. In the Controller Organizer, right-click Main Task and choose
Properties.
Adjust the System
Watchdog Time
Adjust the Watchdog Timer
for a Task
Chapter 1 Manage Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 31
2. On the Task Properties dialog box, select the Configuration tab.
3. Type a numeric value for the watchdog timeout for the task.
4. Select OK.
See also
Adjust the System Watchdog Time on page 30
Adjust the System-overhead Time Slice on page 27
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 33
Chapter 2
Manage Event Tasks
An event task, if configured correctly, interrupts all other tasks for the
minimum amount of time required to respond to the event.
This section describes how to set up event tasks and lists considerations, such
as a higher priority task, that can affect the execution of an event task.
Each event task requires a specific trigger that defines when the task is to run.
The table reviews some of these triggers.
To trigger an event task
when
Use this trigger
With these considerations
Digital input turns On or Off Module Input Data
State Change
• Only one input module can trigger a specific event task.
• The input module triggers the event task based on the change of
state (COS) configuration for the module. The COS configuration
defines which points prompt the module to produce data if they
turn On or Off. This production of data (due to COS) triggers the
event task.
• Typically, enable COS for only one point on the module. If you
enable COS for multiple points, a task overlap of the event task
may occur.
Analog module samples
data
Module Input Data
State Change
• Only one input module can trigger a specific event task.
• The analog module triggers the event task after each real time
sample (RTS) of the channels.
•
All the channels of the module use the same RTS.
Controller gets new data via
a consumed tag
Consumed Tag • Only one consumed can trigger a specific event task.
• Typically, use an IOT instruction in the producing controller to
signal the production of new data. The IOT instruction sets an
event trigger in the producing tag. This trigger passes to the
consumed tag and triggers the event task.
• When a consumed tag triggers an event task, the event task waits
for all the data to arrive before the event task runs.
Registration input for an
axis turns On (or Off)
Axis Registration
1 or 2
• For the registration input to trigger the event task, first run a
Motion Arm Registration (MAR) instruction. This lets the axis
detect the registration input and in turn trigger the event task.
• Once the registration input triggers the event task, run the MAR
instruction again to re-arm the axis for the next registration
input.
• If the scan time of your normal logic is
not
fast enough to re-arm
the axis for the next registration input, consider placing the MAR
instruction within the event task.
Introduction
Choose the trigger for an
event task
Chapter 2 Manage Event Tasks
34 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
To trigger an event task
when
Use this trigger
With these considerations
Axis reaches the position
that is defined as the watch
point
Axis Watch • For the registration input to trigger the event task, first run a
Motion Arm Watch (MAW) instruction. This lets the axis detect the
watch position and in turn trigger the event task.
• Once the watch position triggers the event task, run the MAW
instruction again to re-arm the axis for the next watch position.
• If the scan time of your normal logic is
not
fast enough to re-arm
the axis for the next watch position, consider placing the MAW
instruction within the event task.
Motion planner completes
its execution
Motion Group
Execution
• The base update period for the motion group triggers both the
motion planner and the event task.
• Because the motion planner interrupts all other tasks, it runs
first. If you assign the event task as the highest priority task, it
runs after the motion planner.
Specific condition or
conditions occur within the
logic of a program
EVENT instruction Multiple EVENT instructions can trigger the same task. This lets you
run a task from different programs.
The table lists some example situations for event tasks and the corresponding
triggers.
For this example situation
Use an event task with this trigger
A packaging line glues boxes closed. When a box arrives at the gluing position,
the controller must immediately run the gluing routine.
Module Input Data State Change
A production line uses a proximity sensor to detect the presence of a part.
Because the proximity sensor is on for only a very short time (pulse), the
continuous task might miss the off to on transition of the sensor.
Module Input Data State Change
In an engine test stand, you must capture and archive each sample of analog
data.
Module Input Data State Change
Controller A produces an array of production data for Controller B. You want to
make sure that Controller B does not use the values while Controller A is
updating the array.
Consumed Tag
In a line that packages candy bars, you have to make sure that the perforation
occurs in the correct location on each bar. Each time the registration sensor
detects the registration mark, check the accuracy of an axis and perform any
required adjustment.
Axis Registration 1 or 2
At the labeling station of a bottling line, you want to check the position of the
label on the bottle. When the axis reaches the position that is defined as the
watch point, check the label.
Axis Watch
A gluing station must adjust the amount of glue it applies to compensate for
changes in the speed of the axis. After the motion planner runs, check the
command speed of the axis and vary the amount of glue, if needed.
Motion Group Execution
In a production line, if any of the programs detect an unsafe condition the entire
line must shut down. The shutdown procedure is the same regardless of the
unsafe condition.
EVENT instruction
The triggers that you can use for an event task vary depending on your
controller type.
IMPORTANT
The Logix Designer application may let you configure a trigger for an event task that
your controller does not support. The project verifies and successfully downloads, but
the event task does not run.
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 35
Controller
Applicable event task triggers
Module Input
Data State
Change
Consumed
Tag
Axis
Registration 1
or 2
Axis Watch
Motion Group
Execution
EVENT
instruction
CompactLogix 5370
X X
3
X
3
X
3
X
CompactLogix 5380 X X X
3
X
3
X
3
X
FlexLogix
X
X
ControlLogix
X
X
X
X
X
X
DriveLogix
X X X X X
SoftLogix 5800 X
1
X
2
X
Compact GuardLogix
5370
X X
3
X
3
X
3
X
Compact GuardLogix
5380
X
X
3
X
3
X
3
X
CompactLogix 5480
X
X
X
3
X
3
X
3
X
(1) Requires a 1756 I/O module or a virtual backplane.
(2) A SoftLogix5800 controller produces and consumes tags only over a
ControlNet network.
(3) Motion controller support only.
To trigger an event task based on data from an input module, use the Module
Input Data State Change trigger.
Let an event trigger this task.
Let data from an input module trigger the task.
Let this input tag trigger the task.
Module Input Data State
Change Trigger
Chapter 2 Manage Event Tasks
36 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
Let an event trigger this task.
When the task is done, do not update digital outputs in the local chassis.
These terms apply to the operation of an input module.
Term
Definition
Multicast A mechanism where a module sends data on a network that is simultaneously
received by more than one listener (device). Describes the feature of the Logix 5000
I/O line that supports multiple controllers receiving input data from the same I/O
module at the same time.
Requested packet
interval (RPI)
The RPI specifies the interval that a module multicasts its data. For example, an
input module sends data to a controller at the RPI that you assign to the module.
• The range is 0.2…750 ms.
• When the specified time frame elapses, the module multicasts its data. This is
also called a cyclic update.
Real time sample (RTS) The RTS specifies when an analog module scans its channels and multicasts the
data (update the input data buffer then multicast).
• The RPI specifies when the module multicasts the current contents of the input
data buffer without scanning (updating) the channels.
•
The module resets the RPI timer each time an RTS transfer occurs.
Change of state (COS) The COS parameter instructs a digital input module to multicast data whenever a
specified input point transitions from On → Off or Off → On.
• You enable COS on a per-point basis.
• When any point that is enabled for COS receives the specified change, the module
multicasts the data for all its points.
• By default, COS is enabled for both On → Off and Off → On changes for all points.
• You must specify an RPI regardless of whether you enable COS. If a change does
not occur within the RPI, the module sends its data at the RPI.
The table summarizes when an input module multicasts its data and triggers
an event task within its own chassis.
If the input module is
And
Then it multicasts data
And it triggers an event task
Digital COS is enabled for any point
on the module
• When any point that is enabled for COS receives the
specified change
• At the RPI
When any point that is enabled for COS
receives the specified change
COS is not enabled for any
point on the module
At the RPI Never
Analog RTS ≤ RPI At the RTS (newly updated channel data) At the RTS for the module
RTS > RPI • At the RTS (newly updated channel data)
• At the RPI (does not contain updated data from the
channels)
At the RTS for the module
If the module is in a remote chassis, only the RPI determines when the
controller receives the data and event trigger over the network.
Over this network
Controller receives the data
EtherNet/IP Close to the RPI, on average
ControlNet
At the actual packet interval (≤ RPI)
The examples show COS and RTS configurations.
How an I/O Module Triggers
an Event Task
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 37
IMPORTANT
If you use a digital module to trigger an event task, configure only one point on the
module for COS. If you configure multiple points, a task overlap could occur.
COS and RTS Configuration Examples
If you want this
Then configure the input module like this (Point 0 is an example)
T
o use an input module to trigger an event task, the module must support
event task triggering. If the module is in a remote location, the associated
communication modules must also support event triggering.
Make Sure Your Module Can
Trigger an Event Task
Chapter 2 Manage Event Tasks
38 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
The following table lists Rockwell Automation modules that have been tested
for event task triggering. Some third-party modules may also support event
task triggering. Before you use a third-party module, check with the supplier
to validate the operation of the module.
Category
Modules
Digital I/O modules that support change of state 1756-IA8D
1756-IA16I
1756-IB16
1756-IB16I
1756-IB32
1756-IG16
1756-IH16ISOE
1756-IN16
1756-IV32
1756-IA16
1756-IA32
1756-IB16D
1756-IB16ISOE
1756-IC16
1756-IH16I
1756-IM16I
1756-IV16
Analog I/O modules that support real time sample 1756-IF16
1756-IF6CIS
1756-IF8
1756-IT6I
1756-IF4FXOF2F/A
1756-IF6I
1756-IR6I
1756-IT6I2
Communication modules that provide rack-optimized
connections
1756-CNB/A
1756-CNB/D
1756-CNBR/B
1756-DNB
1756-SYNCH/A
1756-CNB/B
1756-CNBR/A
1756-CNBR/D
1756-ENBT/A
1784-PCIDS/A
Generic I/O modules that conform to CIP event
communication
1756-MODULE
1789-MODULE
Use the following checklist when creating an Input Event Task.
For This
Make Sure You
1. Input module type For the fastest response, use these modules:
• For fastest digital response, use a 1756-IB32/B module.
• For fastest analog response, use a 1756-IF4FXOF2F module.
2. I/O module location Place the module that triggers the event and the modules that respond to the
event (outputs) in the same chassis as the controller.
Remote modules add network communication to the response time.
3. Number of local
modules
Limit the number of modules in the local chassis.
Additional modules increase the potential for backplane delays.
4. Change of state
(COS)
If a digital device triggers the event, enable COS for only the point that triggers
the event task.
• Enable change of state for the type of transition that triggers the task, either
Off → On, On → Off, or both.
• If you configure COS for both Off → On and On → Off, the point triggers an
event task whenever the point turns on or off. Make sure the duration of the
input is longer than the scan time of the task. Otherwise an overlap could
occur.
• Disable (clear) COS for the remaining points on the input module. If you
configure multiple points on a module for COS, each point could trigger the
event task. This could cause an overlap.
Checklist for an Input
Event Task
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 39
5. Task priority Configure the event task as the highest priority task.
If a periodic task has a higher priority, the event task may have to wait until the
periodic task is done.
6. Motion planner The motion planner interrupts all other tasks, regardless of their priority.
• The number of axes and coarse update period for the motion group affect
how long and how often the motion planner executes.
• If the motion planner is executing when a task is triggered, the task waits
until the motion planner is done.
• If the coarse update period occurs while a task is executing, the task pauses
to let the motion planner execute.
7. Number of event
tasks
Limit the number of event tasks.
Each additional task reduces the processing time that is available for other
tasks. This could cause an overlap.
8. Automatic Output
Processing
For an event task, you can typically disable automatic output processing
(default). This reduces the elapsed time of the task.
9. IOT instruction Use an IOT instruction for each output module that you reference in the event
task.
The IOT instruction overrides the RPI for the module and immediately sends the
data.
As parts move past a diverter location, the controller logic determines
whether to turn on the diverter. Once the diverter is on, the controller must
also turn it off before the next part is in that position. Because of the speed of
the line, an event task controls the diverter.
Example – Input Event Task
Chapter 2 Manage Event Tasks
40 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
A photoeye at the diverter position indicates when a part is in the diverter
position. In this example, the input is wired to the module in slot 4 of the local
chassis.
The diverter photoeye (point 0) is configured for change of state for both Off
and On. This lets the photoeye trigger the event task when it turns on and
when it turns off.
The event task uses the following logic to control the diverter.
If Diverter_Photoeye = 1 (part is in the diverter position)
and Divert_Part = 1 (divert this part)
then Diverter = 1 (turn on the diverter)
otherwise Diverter = 0 (turn off the diverter)
Immediately send the output values to the output module in slot 5.
To estimate the throughput time from input to output (screw to screw), use
the following worksheet.
Consideration Value
1. What is the input filter time of the module that triggers the event task? µs
This is typically shown in milliseconds. Convert it to microseconds (µs).
2.
What is the hardware response time for the input module that triggers the event task?
µs
Make sure you use the appropriate type of transition (Off → On or On → Off). See Nominal hardware response
times for the 1756 I/O modules most commonly used with Event tasks later in this section.
3.
What is the backplane communication time?
µs
If chassis size is
Use this value (worst case)
4 slot 13 µs
7 slot
22
µ
s
10 slot 32 µs
13 slot
42
µ
s
17 slot 54 µs
4.
What is the total execution time of the programs of the event task?
µs
Estimate Throughput
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 41
Consideration
Value
5.
What is the backplane communication time? (Same value as step 3.)
µ
s
6.
What is the hardware response time of the output module?
µs
7. Add steps 1...6. This is the minimum estimated throughput, where execution of the motion planner or other tasks do
not
delay or interrupt the event task.
µs
8.
What is the scan time of the motion group?
µs
9.
What is the total scan time of the tasks that have a higher priority than this event task (if any)?
µs
10. Add steps 7...9. This is the nominal estimated throughput, where execution of the motion planner or other tasks delay or
interrupt the event task.
µs
The following table lists nominal hardware response times for 1756 I/O
modules with event tasks.
Cat. No.
Nominal response time µs
25 °C 60 °C
Off → On
On → Off
Off → On
On → Off
1756-IB16 265 582 265 638
1756-IB16D 303 613 305 673
1756-IB32/B 330 359 345 378
1756-IV16 257 435 254 489
1756-IV32
381
476
319
536
1756-OB16D
48
519
51
573
1756-OB16E
60
290
61
324
1756-OB32
38
160
49
179
1756-OV16E
67
260
65
326
1756-OV32E
65
174
66
210
Chapter 2 Manage Event Tasks
42 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
The following example shows the throughput considerations for the system
shown in the following illustration. In this example, the throughput is the
time from when the input turns on to when the output turns on.
Consideration
Value
1. What is the input filter time of the module that triggers the event task? 0 µs
This is typically shown in milliseconds. Convert it to microseconds (µs).
2.
What is the hardware response time for the input module that triggers the event task?
330 µs
Make sure you use the appropriate type of transition (Off → On or On → Off). See the table, earlier in this
section, that lists nominal hardware response times for the 1756 I/O modules most commonly used with Event
tasks.
3.
What is the backplane communication time?
13
µ
s
If chassis size is
Use this value (worst case)
4 slot 13 µs
7 slot 22 µs
10 slot
32
µ
s
13 slot 42 µs
17 slot 54 µs
4. What is the total run time of the programs of the event task? 400 µs
5. What is the backplane communication time? (Same value as step 3.) 13 µs
6.
What is the hardware response time of the output module?
51 µs
7. Add steps 1...6. This is the minimum estimated throughput, where execution of the motion planner or other tasks do
not
delay or
interrupt the event task.
807 µs
8.
What is the scan time of the motion group?
1130
µ
s
9. What is the total scan time of the tasks that have a higher priority than this event task (if any)? 0 µs
10. Add steps 7...9. This is the nominal estimated throughput, where execution of the motion planner or other tasks delay or interrupt the
event task.
1937 µs
Example - Estimate
Throughput
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 43
The following considerations affect the scan time of the event task, which
affects the speed at which it can respond to the input signal.
Consideration
Description
Amount of code in the event task Each logic element (rung, instruction, Structured Text construct, and so
forth) adds scan time to the task.
Task priority If the event task is not the highest priority task, a higher priority task
may delay or interrupt the execution of the event task.
CPS and UID instructions If one of these instructions are active, the event task cannot interrupt
the currently running task. (The task with the CPS or UID.)
To couple the running of an event task with the running of the motion
planner, use the Motion Group Execution trigger.
Let an event trigger this task.
Let the motion planner trigger the task.
This is the name of the motion group tag.
Interrupt all other tasks.
When the task is done, do not update digital outputs in the local chassis.
The Motion Group Execution trigger works as follows:
• The base update period for the motion group triggers the running of
both the motion planner and the event task.
• Because the motion planner interrupts all other tasks, it runs first. If
you assign the event task as the highest priority task, it runs
immediately after the motion planner.
Additional Considerations
Motion Group Trigger
Chapter 2 Manage Event Tasks
44 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
This timing diagram shows the relationship between the motion planner and
the event task.
The Base Update Period for the motion group triggers both the motion
planner and the event task. See the online help for more information on the
Motion Group Properties dialog box.
The following is the checklist for a motion group task:
For This
Make Sure You
1. Scan time Make sure the scan time of the event task is significantly less than the base
update period of the motion group. Otherwise, a task overlap could occur.
Checklist for a Motion
Group Task
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 45
2. Task priority Configure the event task as the highest priority task.
If a periodic task has a higher priority, the event task may have to wait until the
periodic task is finished.
3. Number of event
tasks
Limit the number of event tasks.
Each additional task reduces the processing time that is available for other
tasks. This could cause an overlap.
4. Automatic output
processing
For an event task, you can typically disable automatic output processing
(default). This reduces the elapsed time of the task.
To let the registration input of an axis trigger an event task, use the Axis
Registration 1 or Axis Registration 2 triggers.
Let an event trigger this task.
Let registration input 1….
…of this axis trigger the task.
Interrupt all other tasks.
When the task is done, do not update digital outputs in the local chassis.
When the specified registration input reaches its trigger condition, it triggers
the event task.
• In the configuration of the event task, specify which registration input
you want to trigger the task. Choose either Axis Registration 1 or Axis
Registration 2.
• You must first arm the registration input using a Motion Arm
Registration (MAR) instruction.
Axis Registration Trigger
Chapter 2 Manage Event Tasks
46 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
• In the MAR instruction, the Trigger Condition operand defines which
transition of the registration input (Off → On or On → Off) triggers
the event task.
• Once the registration input triggers the task, you have to re-arm the
registration input.
This timing diagram shows the relationship between the registration input
and the event task.
The following is a checklist for an axis registration task:
For This
Make Sure You
1. Registration
input
Arm the registration input (MAR instruction). This lets the axis detect the
registration input and trigger the event task.
• Initially, arm the registration input to detect the first trigger condition.
• Re-arm the registration input after each execution of the event task.
•
Re-arm the registration input fast enough to detect each trigger condition.
If your normal logic is Then
Fast enough to re-arm the registration
input between intervals of the trigger
condition
For example, normal logic always
completes at least two scans between
registration inputs.
Arm the registration input within your
normal logic, if desired.
Not fast enough to re-arm the registration
input
Arm the registration input within the
event task.
2. Task priority Configure the event task as the highest priority task.
If a periodic task has a higher priority, the event task may have to wait until the
periodic task is finished.
3. Number of event
tasks
Limit the number of event tasks.
Each additional task reduces the processing time that is available for other tasks.
This could cause an overlap.
4. Automatic
output
processing
For an event task, you can typically disable automatic output processing (default).
This reduces the elapsed time of the task.
Checklist for an Axis
Registration Task
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 47
In a line that packages candy bars, you have to make sure that the perforation
occurs in the correct location on each bar.
• Each time the registration sensor detects the registration mark, check
the accuracy of an axis and perform any required adjustment.
• Due to the speed of the line, you have to arm the registration input
within the event task.
A registration sensor is wired as registration input 1…
…for the axis named
Axis_1
.
This event task interrupts all other tasks.
The following logic arms and re-arms the registration input.
Continuous task
If Arm_Registration = 1 (system is ready to look for the registration mark) then
the ONS instruction limits the EVENT instruction to one scan.
the EVENT instruction triggers Task_1 (event task).
Task_1 (event task)
The GSV instruction sets Task_Status (DINT tag) = Status attribute for the event task. In the Instance Name
attribute, THIS means the TASK object for the task that the instruction is in (that is, Task_1).
If Task_Status.0 = 1 then an EVENT instruction triggered the event task. In the continuous task, the EVENT
runs to arm registration for the first time.
Example - Axis
Registration Trigger
Chapter 2 Manage Event Tasks
48 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
The JMP instruction causes the controller to jump to the Arm LBL instruction. This skips all the logic of the
routine except the rung that arms registration for the axis.
• Other logic
The MAR instruction runs each time the task runs and arms Axis_1 for registration.
The OTU instruction sets the EN bit of the MAR instruction = 0.
• The MAR instruction is a transitional instruction.
• For the MAR instruction to run, its rung-condition-in must go from false to true.
• By first clearing the EN bit, the instruction responds as if its rung-condition-in changed from false to true.
The MAR instruction arms the axis for registration.
The controller does not clear the bits of the Status attribute once they are set. To use a bit for new status
information, you must manually clear the bit.
If Task_Status.0 = 1 then clear that bit.
The OTU instruction sets Task_Status.0 = 0.
The SSV instruction sets the Status attribute of THIS task (Task_1) = Task_Status. This includes the cleared
bit.
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 49
To configure the watch position of an axis to trigger an event task, use the
Axis Watch trigger.
Let an event trigger this task.
Let the watch position….
…of this axis trigger the task.
Interrupt all other tasks.
When the task is done, do not update digital outputs in the local chassis.
When the axis reaches the position that is specified as the watch position, it
triggers the event task.
• You must first arm the axis for the watch position by using a Motion
Arm Watch (MAW) instruction.
• In the MAW instruction, the Trigger Condition operand defines the
direction in which the axis must be moving to trigger the event task.
• Once the axis reaches the watch position and triggers the event task,
you have to re-arm the axis for the next watch position.
Axis Watch Trigger
Chapter 2 Manage Event Tasks
50 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
This timing diagram shows the relationship between the watch position and
the event task.
The following is a checklist for an axis watch task:
For This Make Sure You
1. Watch position Use a MAW instruction to set up a watch position. This lets the axis trigger the
event task when it reaches the watch position.
• Initially, arm the axis to detect the first watch position.
• When the axis reaches the watch position and triggers the event task, re-arm the
axis for the next watch position.
• Re-arm the axis fast enough to detect each watch position.
If your normal logic is
Then
Fast enough to re-arm the axis between
intervals of the watch position
(For example, normal logic always
completes at least two scans between
watch positions.)
Arm the axis within your normal logic, if
desired.
Not fast enough to re-arm the axis Arm the axis within the event task.
2. Task priority Configure the event task as the highest priority task.
If a periodic task has a higher priority, the event task may have to wait until the
periodic task is finished.
3. Number of event
tasks
Limit the number of event tasks.
Each additional task reduces the processing time that is available for other tasks.
This could cause an overlap.
4. Automatic
output
processing
For an event task, you can typically disable automatic output processing (default).
This reduces the elapsed time of the task.
At the labeling station of a bottling line, you want to check the position of the
label on the bottle.
• When the axis reaches the position that is defined as the watch point,
check the label and perform any required adjustment.
Checklist for an Axis
Watch Task
Example - Axis
Watch Trigger
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 51
• Due to the speed of the line, you have to arm axis for the watch
position within the event task.
Let the watch position…
…for the axis named Axis_1 trigger the event task..
This event task interrupts all other tasks.
The following logic arms and re-arms the axis for the watch position.
Continuous task
If Arm_Watch = 1 (system is ready to set up a watch position) then
the ONS instruction limits the EVENT instruction to one scan.
the EVENT instruction triggers Task_1 (event task).
Task_1 (event task)
The GSV instruction sets Task_Status (DINT tag) = Status attribute for the event task. In the Instance Name
attribute, THIS means the Task object for the task that the instruction is in (that is, Task_1).
If Task_Status.0 = 1 then an EVENT instruction triggered the event task. In the continuous task, the EVENT
runs to set up the watch position for the first time.
Chapter 2 Manage Event Tasks
52 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
The JMP instruction causes the controller to jump to the Arm LBL instruction. This skips all the logic of the
routine except the rung that arms the axis for the watch position (MAW instruction).
•
Other logic
The MAW instruction runs each time the task runs and arms Axis_1 for the watch position.
The OTU instruction sets the EN bit of the MAW instruction = 0.
• The MAW instruction is a transitional instruction.
• To run the MAW instruction, its rung-condition-in must go from false to true.
•
By first clearing the EN bit, the instruction responds as if its rung-condition-in changed from false to true.
The MAW instruction arms the axis for the watch position.
The controller does not clear the bits of the Status attribute once they are set. To use a bit for new status
information, you must manually clear the bit.
If Task_Status.0 = 1 then clear that bit.
The OTU instruction sets Task_Status.0 = 0.
The SSV instruction sets the Status attribute of THIS task (Task_1) = Task_Status. This includes the cleared
bit.
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 53
To trigger an event task based on data from a consumed tag, use the
Consumed Tag trigger.
Let an event trigger this task.
Let a consumed tag trigger the task.
Let this consumed tag trigger the task.
A produced/consumed tag relationship can pass an event trigger along with
data to a consumer controller. Typically, you use an Immediate Output (IOT)
instruction to send the event trigger to the consumer controller.
Consumed Tag Trigger
Chapter 2 Manage Event Tasks
54 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
Description
In Controller A, logic updates the values of a produced tag.
Once the update is complete, the Controller A runs an IOT instruction to send the data and an
event trigger to Controller B.
Controller B consumes the new data.
After Controller B updates the consumed tag, it runs the event task.
The type of network between the controllers determines when the consuming
controller receives the new data and event trigger through the IOT
instruction.
The following table lists the times when the consuming device receives the
new data and event trigger.
With this controller
Over this network
The consuming device receives the data and
event trigger
ControlLogix Backplane Immediately
EtherNet/IP network Immediately
ControlNet network Within the actual packet interval (API) of the
consumed tag (connection)
SoftLogix5800 You can produce and consume tags only over a
ControlNet network
Within the actual packet interval (API) of the
consumed tag (connection)
The following diagrams compare the receipt of data via an IOT instruction
over EtherNet/IP and ControlNet networks.
EtherNet/IP Network (ControlLogix controller)
ControlNet Network
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 55
An event task with a consumed tag trigger provides a simple mechanism to
pass data to a controller and make sure that the controller doesn’t use the data
while the data is changing.
Description
RPI occurs for the produced tag.
The produced tag transfers old data to the consuming controller.
The producer controller starts to update the values of the produced tag.
RPI occurs again for the produced tag.
The produced tag transfers a mix of old and new data to the consuming controller.
The producer controller finishes updating the values of the produced tag.
The producer controller runs an Immediate Output (IOT) instruction.
The produced tag immediately transfers all the new data to the consuming controller.
When the consumer controller receives all the data, it runs its event task.
Although the producing controller runs the IOT instruction immediately after
it loads new data, the event task is not triggered (in the consuming controller)
until the consuming controller has received all the new data. This verifies that
the controller operates on a complete packet of new data.
Use the produced/consumed tag relationship to synchronize controllers. In
this case, the produced/consumed tag serves only as a triggering mechanism..
Maintain the Integrity
of Data
Synchronize multiple
controllers
Chapter 2 Manage Event Tasks
56 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
Description
The first controller runs an action with which other controllers need to stay synchronized.
When the action is done, the controller runs an IOT instruction. The IOT instruction uses a
produced tag as its target.
When controller A receives the produced tag, it runs its event task.
When controller B receives the produced tag, it runs its event task.
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 57
The following is a checklist for the producer controller:
Make Sure You
1. Buffer of data If
you want to send a complete image of data at one instance in time, then produce a copy of the data, as shown in
the following illustration.
2.
Produced tag
properties
On the New Tag dialog box for the produced tag, click Connection to open the Produced Tag Connection dialog box.
Check
Send Data State Change Event to Consumer(s)
.
If you leave this checkbox cleared (unchecked), the producing controller triggers the event task at the end of any task
that
automatically updates local outputs. In other words, the task scan triggers the event in addition to the
IOT instruction.
3. IOT
i
nstruction
Use an IOT instruction at the point in your logic where you want to trigger the event task.
The IOT instruction overrides the RPI for the tag and immediately sends the event trigger and the data of the tag.
Checklist for the
Producer
Controller
For This
Chapter 2 Manage Event Tasks
58 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
The following is a checklist for the consumer controller:
For This
Make Sure You
1. B
uffer of data If you want to make sure that the controller does not use data from the consumed tag
while the data is changing, use a copy of the consumed tag. Use the event task to copy
the data, as shown in the Event Task diagram.
2. T
ask priority Configure the event task as the highest priority task.
If a periodic task has a higher priority, the event task may have to wait until the periodic
task is finished.
3. N
umber of event
tasks
Limit the number of event tasks.
Each additional task reduces the processing time that is available for other tasks. This
could cause an overlap.
4. A
utomatic
output
processing
For an event task, you can typically disable automatic output processing (default). This
reduces the elapsed time of the task.
A
s parts move along a production line, each station requires production
specifications for the part at its station. To make sure that a station doesn’t
act on old data, an event task signals the arrival of new data for the next part.
Producer Controller
This controller controls station 24 and produces data for the next station
(station 25). To signal the transmission of new data, the controller uses the
following elements:
• Produced_Tag
• Ladder logic
Produced Tag Properties
Checklist for the Consumer
Controller
Example - Producer
Controller and
Consumer Controller
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 59
Produced_Tag is configured to update its event trigger through an IOT
instruction.
Ladder Logic
If New_Data = on, then this occurs for one scan.
The CPS instruction sets Produced_Tag_1 = Source_Tag_1.
The IOT instruction updates Produced_Tag_1 and sends this update to the consuming controller (station
25). When the consuming controller receives this update, it triggers the associated event task in that
controller.
Consumer Controller
The controller at station 25 uses the data produced by station 24. To determine
when new data has arrived, the controller uses an event task.
Event Task Properties
Chapter 2 Manage Event Tasks
60 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
Let an event trigger this task.
Let a consumed tag trigger the task.
Let this consumed tag trigger the task.
Ladder Diagram in the Event Task
When the event task runs, the CPS instruction sets Destination_Tag_1 = Consumed_Tag_1 (the values from
the producing controller). The remaining logic in this controller uses the values from Destination_Tag_1.
To trigger an event task based on conditions in your logic, use the EVENT
Instruction Only trigger.
Let an event trigger this task.
Let an EVENT instruction trigger the task.
No tag is required.
EVENT Instruction Trigger
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 61
The EVENT Instruction Only trigger requires that you use a Trigger Event
Task (EVENT) instruction to trigger the task. You can use an EVENT
instruction from multiple points in your project. Each time the instruction
runs, it triggers the specified event task.
Description
Program A runs an EVENT instruction.
The event task that is specified by the EVENT instruction runs one time.
Program B runs an EVENT instruction.
The event task that is specified by the EVENT instruction runs one time.
To determine if an EVENT instruction triggered an event task, use a
Get System Value (GSV) instruction to monitor the Status attribute of the
task.
Table 8 - Status Attribute of the TASK Object
Attribute
Data Type
Instruction
Description
Status DINT GSV
SSV
Provides status information about the task. Once the controller sets a bit, you must manually
clear the bit to determine if another fault of that type occurred.
To determine if
Examine this bit
An EVENT instruction triggered the task (event task only). 0
A timeout triggered the task (event task only). 1
An overlap occurred for this task.
2
The controller does not clear the bits of the Status attribute once they are set.
• To use a bit for new status information, you must manually clear the
bit.
• Use a Set System Value (SSV) instruction to set the attribute to a
different value.
Programmatically
Determine if EVENT
Instruction Triggered Task
Chapter 2 Manage Event Tasks
62 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
The following is checklist for an EVENT instruction task:
For This
Make Sure You
1. EVENT instruction Use a
Trigger Event Task (EVENT)
instruction at each point in your logic that
you want to trigger the event task.
2. Task priority Configure the event task as the highest priority task.
If a periodic task has a higher priority, the event task may have to wait until
the periodic task is finished.
3. Number of event tasks Limit the number of event tasks.
Each additional task reduces the processing time that is available for other
tasks. This could cause an overlap.
4. Automatic output
processing
For an event task, you can typically disable automatic output processing
(default). This reduces the elapsed time of the task.
A controller uses multiple programs except for a common shut down
procedure. Each program uses a program-scoped tag named
Shut_Down_Line that turns on if the program detects a condition that
requires a shut down.
Event Task Properties
Let an event trigger this task.
Let an EVENT instruction trigger the task.
No tag is required.
Interrupt all other tasks.
Checklist for an EVENT
Instruction Task
Example – EVENT
Instruction Trigger
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 63
Ladder Diagram in Program_A
If Shut_Down_Line = on (conditions require a shut down) then
run the Shut_Down task one time.
Ladder Diagram in Program_B
If Shut_Down_Line = on (conditions require a shut down) then
run the Shut_Down task one time.
If you want your event task to run automatically, if the trigger fails to occur
within a certain time, assign a timeout value to the task. When the event task
is finished, the timeout timer begins to increment. If the timer reaches its
preset value before the event task is triggered, the event task runs
automatically.
Description
Event task runs.
Timeout time stops incrementing.
Event task is done.
Timeout timer resets and begins incrementing.
Timeout timer reaches the timeout value.
Event task automatically runs.
In the Status attribute of the TASK object, bit 1 turns on.
Follow these steps to assign a timeout value to an event task.
Define a Timeout Value for
an Event Task
Assign a Timeout Value to
an Event Task
Chapter 2 Manage Event Tasks
64 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
To assign a timeout value to an event task
1. In the Controller Organizer, right-click Main Task and
choose Properties.
2. On the Task Properties dialog box, select the Configuration tab.
3. From the Type menu, choose Event.
4. Select Execute Task If No Event Occurs Within.
5. Type the timeout value.
6. Select OK.
To programmatically configure a timeout, use a Get System Value (GSV)
instruction to access the attributes of the task. The following table lists the
status attribute for the TASK object.
Programmatically Configure
a Timeout
Chapter 2 Manage Event Tasks
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 65
Attribute
Data Type
Instruction
Description
Rate
DINT
GSV
SSV
If the task type is
Then the Rate attribute specifies the
Periodic Period for the task. Time is in microseconds.
Event The timeout value for the task. Time is in
microseconds.
EnableTimeOut DINT GSV
SSV
Enables or disables the timeout Function of an event task.
To
Set the attribute to
Disable the timeout function 0 (default)
Enable the timeout function 1 (or any non-zero value)
Example
To make sure that a timeout value is always defined and enabled for an event
task, the logic configures the timeout when the controller enters Run mode.
If S:FS = 1 (first scan) then set the timeout value for Task_2 and enable the
timeout function.
1. The first MOV instruction sets Task_2_Timeout = 10000000 µs (DINT
value). Then the SSV instruction sets the Rate attribute for Task_2 =
Task_2_Timeout. This configures the timeout value for the task.
2. The second MOV instruction sets One = 1 (DINT value). Then the SSV
instruction sets the EnableTimeout attribute for Task_2 = One. This
enables the timeout function for the task.
To determine if an event task ran due to a timeout, use a Get System
Value (GSV) instruction to monitor the Status attribute of the task. The
following table lists the Status attribute for the TASK object.
Attribute
Data
Type
Instruction
Description
Status DINT GSV
SSV
Provides status information about the task. Once the controller sets a bit, you
must manually clear the bit to determine if another fault of that type occurred.
To determine if
Examine this bit
Programmatically
determine if a
timeout occurs
Chapter 2 Manage Event Tasks
66 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
Attribute
Data
Type
Instruction
Description
An EVENT instruction triggered the task
(event task only).
0
A timeout triggered the task (event task
only).
1
An overlap occurred for this task.
2
Example
If a timeout occurs for the event task, communication with the triggering
device might have failed. This requires the process to shut down. To shut
down the controller, the event task calls the fault routine for the program and
supplies a user-defined fault code (999 in this example).
1. The GSV instruction sets Task_2_Status = Status attribute for Task_2
(DINT value).
2. If Task_2_Status.1 = 1, then a timeout occurred so shut down the
controller and set the major fault code to 999.
The JSR instruction calls the fault routine for the program. This
produces a major fault.
The major fault code = 999 (value of the input parameter of 999).
3. If Condition_1 = 1, then clear the bits of the Status attribute for Task_2.
The SSV instruction sets the Status attribute of Task_2 = Zero. Zero is a
DINT tag with a value of 0.
Index
Rockwell Automation Publication 1756-PM005K-EN-P - November 2022 67
Index
C
change of state
configure for I/O module 36
communication
impact on execution 12
configure
output processing for a task 17
consumed tag
maintain data integrity 55
synchronize controllers 55
controller
number of tasks 9
synchronize 55
COS. See change of state 36
create
periodic task 25
E
event task
axis registration trigger 45
axis watch trigger 49
checklist for consumed tag event 57,
58
checklist for input event 38
checklist for motion group event 44
checklist for registration event 46
checklist for watch position event 50
choose trigger 33
consumed tag trigger 53
estimate throughput 40
EVENT trigger 60
input data trigger 35
motion group trigger 43
timeout 63
execute
event task 33
I
I/O
impact on execution 12
output processing 17
throughput for event task 40
I/O module
choose for event task 37
configure change of state 36
trigger event task 36
inhibit
task 21
M
monitor
task 15
motion planner
impact on execution 12
trigger event task 43
O
output processing
manually configure 20
overview 17
programmatically configure 21
overlap
manually check for 15
overview 14
programmaticlly check for 16
overrun. See overlap 14
P
periodic task
create 25
project
number of tasks 9
R
registration
trigger event task 45
S
synchronize
controllers 55
system overhead time slice
impact on executon 12
T
tag
trigger event task 53
Index
68 Rockwell Automation Publication 1756-PM005K-EN-P - November 2022
task
avoid overlap 14
choose event trigger 33
create periodic 25
define timeout 63
inhibit 21
manually check for overlap 15
manually configure output processing
20
monitor 15, 16
number supported 9
output processing 17
overlap 14
programmatically check for overlap 16
programmatically configure output
processing 21
trigger via EVENT instruction 60
throughput
estimate for event task 40
timeout
define for event task 63
trigger
axis registration 45
axis watch 49
choose for event task 33
consumed tag 53
EVENT instruction 60
module input data 35
motion group 43
W
watch point
trigger event task 49
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