Rockwell Automation Allen-Bradley Logix 5000 Series Owner's manual

Programming Manual
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

Important user information
Read this document and the documents listed in the additional resources section about installation, configuration, and operation of this equipment
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Trademarks not belonging to Rockwell Automation are property of their respective companies.

Rockwell Automation Publication 1756-PM005H-EN-P - February 2018 3
Summary of changes
This manual contains new and updated information. There are a number of minor
changes throughout this publication that were made to clarify existing
information. The major changes are listed in the following table.
Change Topic
Updated the list of supported controllers. Cover
Updated screen shots. Throughout

Rockwell Automation Publication 1756-PM005H-EN-P - February 2018 5
Table of contents
Studio 5000 environment....................................................................................................7
Additional resources.............................................................................................................7
Legal notices ...........................................................................................................................8
Chapter 1
Introduction........................................................................................................................ 11
Select Controller Tasks..................................................................................................... 11
Use Caution in the Number of Tasks That You Use......................................... 13
Prioritize Periodic and Event tasks................................................................................. 13
Additional Considerations....................................................................................... 14
Example ........................................................................................................................ 15
Leave Enough Time for Unscheduled Communication............................................ 16
Avoid Overlaps ................................................................................................................... 17
Manually Check for Overlaps.................................................................................. 18
Programmatically Check for Overlaps................................................................... 19
Configure Output Processing for a Task....................................................................... 21
Manually Configure Output Processing ............................................................... 23
Programmatically Configure Output Processing ................................................ 24
Inhibit a Task...................................................................................................................... 25
Manually Inhibit or Uninhibit a Task................................................................... 25
Programmatically Inhibit or Uninhibit a Task .................................................... 26
Create a Task....................................................................................................................... 27
Create a Periodic Task............................................................................................... 29
Language Switching ................................................................................................... 30
Adjust the System-overhead Time Slice ........................................................................ 31
Configure the System-overhead Time Slice.......................................................... 32
Adjust the System Watchdog Time ............................................................................... 34
Adjust the Watchdog Timer for a Task................................................................. 34
Chapter 2
Introduction........................................................................................................................ 37
Choose the trigger for an event task............................................................................... 37
Module Input Data State Change Trigger.................................................................... 40
How an I/O Module Triggers an Event Task...................................................... 40
Make Sure Your Module Can Trigger an Event Task........................................ 43
Checklist for an Input Event Task.......................................................................... 43
Example – Input Event Task ................................................................................... 45
Estimate Throughput................................................................................................ 46
Example - Estimate Throughput............................................................................. 47
Additional Considerations....................................................................................... 48
Motion Group Trigger...................................................................................................... 49
Preface
Manage Tasks
Manage Event Tasks

Table of contents
6Rockwell Automation Publication 1756-PM005H-EN-P - February 2018
Checklist for a Motion Group Task....................................................................... 51
Axis Registration Trigger.................................................................................................. 51
Checklist for an Axis Registration Task ................................................................ 52
Example - Axis Registration Trigger....................................................................... 53
Axis Watch Trigger............................................................................................................ 55
Checklist for an Axis Watch Task.......................................................................... 56
Example - Axis Watch Trigger................................................................................. 56
Consumed Tag Trigger..................................................................................................... 59
Maintain the Integrity of Data ................................................................................ 61
Synchronize multiple controllers............................................................................ 62
Checklist for the Producer Controller................................................................... 62
Checklist for the Consumer Controller................................................................ 63
Example - Producer Controller and Consumer Controller .............................. 64
Producer Controller .................................................................................................. 64
Produced Tag Properties................................................................................... 65
Ladder Logic........................................................................................................ 65
Consumer Controller................................................................................................ 65
Event Task Properties........................................................................................ 65
Ladder Diagram in the Event Task................................................................. 66
EVENT Instruction Trigger............................................................................................ 67
Programmatically Determine if EVENT Instruction Triggered Task............ 68
Checklist for an EVENT Instruction Task .......................................................... 68
Example – EVENT Instruction Trigger................................................................ 69
Event Task Properties........................................................................................ 69
Ladder Diagram in Program_A....................................................................... 69
Ladder Diagram in Program_B ....................................................................... 69
Define a Timeout Value for an Event Task .................................................................. 70
Assign a Timeout Value to an Event Task ............................................................ 71
Programmatically Configure a Timeout................................................................ 72
Programmatically determine if a timeout occurs................................................. 72
Index

Rockwell Automation Publication 1756-PM005H-EN-P - February 2018 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 that is based on the Logix
5000 operating system.
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.
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.
Studio 5000 environment
Additional resources

Preface
8Rockwell Automation Publication 1756-PM005H-EN-P - February 2018
You can view or download publications at
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technical documentation, contact your local Rockwell Automation distributor or
sales representative.
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Printed in USA.
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Trademark Notices
Allen-Bradley, ControlBus, ControlFLASH, Compact GuardLogix, Compact
I/O, ControlLogix, CompactLogix, DCM, DH+, Data Highway Plus,
DriveLogix, DPI, DriveTools, Explorer, FactoryTalk, FactoryTalk Administration
Console, FactoryTalk Alarms and Events, FactoryTalk Batch, FactoryTalk
Directory, FactoryTalk Security, FactoryTalk Services Platform, FactoryTalk
Legal notices

Preface
Rockwell Automation Publication 1756-PM005H-EN-P - February 2018 9
View, FactoryTalk View SE, FLEX Ex, FlexLogix, FLEX I/O, Guard I/O, High
Performance Drive, Integrated Architecture, Kinetix, Logix5000, Logix 5000,
Logix5550, MicroLogix, DeviceNet, EtherNet/IP, PLC-2, PLC-3, PLC-5,
PanelBuilder, PowerFlex, PhaseManager, POINT I/O, PowerFlex, Rockwell
Automation, RSBizWare, Rockwell Software, RSEmulate, Historian,
RSFieldbus, RSLinx, RSLogix, RSNetWorx for DeviceNet, RSNetWorx for
EtherNet/IP, RSMACC, RSView, RSView32, Rockwell Software Studio 5000
Automation Engineering & Design Environment, Studio 5000 View Designer,
SCANport, SLC, SoftLogix, SMC Flex, Studio 5000, Ultra 100, Ultra 200,
VersaView, WINtelligent, XM, SequenceManager are trademarks of Rockwell
Automation, Inc.
Any Rockwell Automation logo, software or hardware product not mentioned
herein is also a trademark, registered or otherwise, of Rockwell Automation, Inc.
Other Trademarks
CmFAS Assistant, CmDongle, CodeMeter, CodeMeter Control Center, and
WIBU are trademarks of WIBU-SYSTEMS AG in the United States and/or
other countries. Microsoft is a registered trademark of Microsoft Corporation in
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ControlNet International. DeviceNet is a trademark of the Open DeviceNet
Vendors Association (ODVA). Ethernet/IP is a trademark of ControlNet
International under license by ODVA.
All other trademarks are the property of their respective holders and are hereby
acknowledged.
Warranty
This product is warranted in accordance with the product license. The product’s
performance may be affected by system configuration, the application being
performed, operator control, maintenance, and other related factors. Rockwell
Automation is not responsible for these intervening factors. The instructions in
this document do not cover all the details or variations in the equipment,
procedure, or process described, nor do they provide directions for meeting every
possible contingency during installation, operation, or maintenance. This
product’s implementation may vary among users.
This document is current as of the time of release of the product; however, the
accompanying software may have changed since the release. Rockwell Automation,
Inc. reserves the right to change any information contained in this document or
the software at any time without prior notice. It is your responsibility to obtain the
most current information available from Rockwell when installing or using this
product.

Preface
10 Rockwell Automation Publication 1756-PM005H-EN-P - February 2018
Environmental compliance
Rockwell Automation maintains current product environmental information on
its website at http://www.rockwellautomation.com/rockwellautomation/about-
us/sustainability-ethics/product-environmental-compliance.page
Contact Rockwell Automation
Customer Support Telephone — 1.440.646.3434
Online Support — http://www.rockwellautomation.com/support/

Rockwell Automation Publication 1756-PM005H-EN-P - February 2018 11
Chapter 1
Manage Tasks
The default project provides a single task for all your logic. Although this is
sufficient for many applications, some situations may require more than one task.
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.
•A different 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.
Introduction
Select Controller Tasks

Chapter 1
Manage Tasks
12 Rockwell Automation Publication 1756-PM005H-EN-P - February 2018
If you want to run a section of
your logic
Then use this type
of task
Description
•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.
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 registrationmark,
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.

Manage Tasks
Chapter 1
Rockwell Automation Publication 1756-PM005H-EN-P - February 2018 13
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.
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.
•Other tasks 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
Use Caution in the Number of
Tasks That You Use
Prioritize Periodic and
Event tasks

Chapter 1
Manage Tasks
14 Rockwell Automation Publication 1756-PM005H-EN-P - February 2018
This Logix 5000 controller Has this many priority levels
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.
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
Additional Considerations

Manage Tasks
Chapter 1
Rockwell Automation Publication 1756-PM005H-EN-P - February 2018 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 on page 14.
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
Example

Chapter 1
Manage Tasks
16 Rockwell Automation Publication 1756-PM005H-EN-P - February 2018
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.
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.
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.
Leave Enough Time for
Unscheduled
Communication

Manage Tasks
Chapter 1
Rockwell Automation Publication 1756-PM005H-EN-P - February 2018 17
•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.
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.
Avoid Overlaps

Chapter 1
Manage Tasks
18 Rockwell Automation Publication 1756-PM005H-EN-P - February 2018
Follow these steps to manually see if overlaps are occurring for a task.
1. In the Controller Organizer, right-click MainTask and choose Properties.
Manually Check for Overlaps

Manage Tasks
Chapter 1
Rockwell Automation Publication 1756-PM005H-EN-P - February 2018 19
2. On the Task Properties dialog box, click the Monitor tab.
The Task Overlap Count shows the number of overlaps since the counter
was last reset.
3. Click OK.
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
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.
Programmatically Check for
Overlaps

Chapter 1
Manage Tasks
20 Rockwell Automation Publication 1756-PM005H-EN-P - February 2018
If you want to Then access the object and attribute
Object Attribute Data Type Description
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.