Allen-Bradley GuardLogix 1756, SoftLogix 1789, Logix5000, CompactLogix 1769, CompactLogix 5370 Reference Manual
...
Reference Manual
Logix5000 Controllers Design Considerations
Catalog Numbers 1756 ControlLogix, 1756 GuardLogix, 1768 CompactLogix, 1768 Compact GuardLogix, 1769 CompactLogix,
1789 SoftLogix, CompactLogix 5370
AB Drives
Important User Information
IMPORTANT
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.
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: Labels may be on or inside the equipment, for example, a drive or motor, to alert people that surfaces may
reach dangerous temperatures.
ARC FLASH HAZARD: Labels may be on or inside the equipment, for example, a motor control center, to alert people to
potential Arc Flash. Arc Flash will cause severe injury or death. Wear proper Personal Protective Equipment (PPE). Follow ALL
Regulatory requirements for safe work practices and for Personal Protective Equipment (PPE).
Allen-Bradley, CompactBlock Guard I/O, CompactLogix, ControlFLASH, ControlLog ix, DH+, FactoryTalk, FLEX, GuardLogix, Kinetix, L ogix5000, MicroLogix, PanelBuilder, PanelView, PhaseManager, PLC-2, PLC-3,
PLC-5, POINT I/O, POIN T Guard I/O, Rockwell Automation, Rockwell Software, RSBizWare, RSFieldbus, RSLinx, RSLogix 5000, RSNetWorx, RSView, SLC, SoftLogix, Stratix, Stratix 2000, Stratix 5700, Stratix 6000,
Stratix 8000, Stratix 83 00, Studio 5000, Studi o 5000 Logix Desig ner, SynchLink, and Ultra are trademark s of Rockwell Automation, Inc.
ControlNet, DeviceNet, and EtherNet/IP are trademarks of ODVA, Inc.
Trademarks not belonging to Rockwell Automation are property of their respective companies.
Logix5000 Controller Comparison - CompactLogix, ControlLogix, GuardLogix
Table 1 - CompactLogix, ControlLogix, and GuardLogix Characteristics
Characteristic CompactLogix™
Controller tasks:
• Continuous
•Periodic
•Event
Event tasks Consumed tag, EVENT
User memory • 1769-L30ER,
Memory card Secure Digital Secure Digital Secure Digital Secure Digital
Built-in ports 2 EtherNet/IP and 1 USB 2 EtherNet/IP and 1 USB 2 EtherNet/IP and 1 USB 1 USB
Communication options •Dual EtherNet/IP ports
Controller connections 256 256 256 500
Network connections • 1769-L30ER,
Controller redundancy — — — Supported with restrictions
Integrated motion 1769- L30ERM, 1769-L33ERM,
Programming languages • • Relay ladder
1769-L30ER,
1769-L30ER-NSE,
1769-L30ERM,
1769-L33ER,
1769-L33ERM,
1769-L36ERM
32
•100 programs/task,
Version 23 and earlier
• 1000 programs/task, max:
Version 24 or later
instruction, axis, and motion
event triggers
1769-L30ER-NSE,
1769-L30ERM: 1MB
• 1769-L33ER,
1769-L33ERM: 2 MB
• 1769-L36ERM: 3 MB
• DeviceNet
1769-L30ER-NSE, 1769L30ERM: 16
• 1769-L33ER,
1769-L33ERM: 32
• 1769-L36ERM: 48
and 1769-L36ERM support
integrated motion on an
EtherNet/IP network
•• Structured text
• • Function block
•• SFC
CompactLogix
1769-L24ER-BB1B,
1769-L24ER-QBFC1B,
1769-L27ERM-QBFC1B
32
• 100 programs/task, Version
23 and earlier
• 1000 programs/task, max:
Vers ion 2 4 or l ater
Consumed tag, EVENT
instruction, axis, and m25-
7.50otion event triggers
• 1769-L24ER: 750 KB
• 1769-L27ERM: 1 MB
• Dual EtherNet/IP ports
• DeviceNet
• 1769-L24ER-BB1B,
1769-L24ER-QBFC1B, 8
• 1769-L27ERM-QBFC1B, 16
1769-L27ERM-QBFC1B supports
integrated motion on an
EtherNet/IP network
• • Relay ladder
•• Structured text
•• Function block
•• SFC
CompactLogix
1769-L16ER-BB1B,
1769-L18ER-BB1B,
1769-L18ERM-BB1B
32
• 100 programs/task, Version 23 and earlier
• 1000 programs/task, max: Version 24 or
later
Consumed tag, EVENT instruction, axis, and
motion event triggers; this controller also
executes an Event task from its embedded I/O
modules
• 1769-L16ER: 384 KB
• 1769-L18ER,
1769-L18ERM: 512 KB
• Dual EtherNet/IP ports • EtherNet/IP (standard and safety)
• 1769-L16ER-BB1B: 4
• 1769-L18ER-BB1B, 1769-L18ERM-BB1B: 8
1769-L18ERM-BB1B supports integrated
motion on an EtherNet/IP network
• • Relay ladder
•• Structured text
• • Function block
•• SFC
ControlLogix®
1756-L71, 1756-L72, 1756-L73,
1756-L74, 1756-L75, 1756-L73XT
GuardLogix®
1756-L72S, 1756-L73S, 1756-L73SXT
32
• 100 programs/task, Version 23 and earlier
• 1000 programs/task, max: Version 24 or later
All event triggers
• 1756-L71: 2 MB
• 1756-L72: 4 MB
• 1756-L72S, 1756-L73SXT: 4 MB + 2 MB safety
• 1756-L73, 1756-L73XT: 8 MB
• 1756-L73S: 8 MB + 4 MB safety
• 1756-L74: 16 MB
• 1756-L75: 32 MB
• ControlNet (standard and safety)
• DeviceNet (standard and safety)
•DH+™
• Remote I/O
•SynchLink™
Per mo dule:
• 128 ControlNet (CN2/B)
• 40 ControlNet (CNB)
• 256 EtherNet/IP; 128 TCP (EN2x)
• 128 EtherNet/IP; 64 TCP (ENBT)
Integrated motion on an EtherNet/IP network
SERCOS interface
Analog options
• Standard task: all languages
• Safety task: relay ladder, safety application
instructions
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Rockwell Automation Publication 1756-RM094I-EN-P - September 2015 3
Chapter 1
Notes:
4 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
Summary of Changes
This manual contains new and updated information. Changes throughout this
revision are marked by change bars, as shown to the right of this paragraph.
Top ic Pag e
Logix5000™ Controller Comparison Table:
• Removed 1756-L6x, 1769-L23x, 1769-L3x, and 1769-L4x because they are no longer supported.
• Removed SoftLogix™ 5800 because the controller does not support the features in Studio 5000
Logix Designer Version® 24, but the controller does support Emulator in Version 24.
• Changed 1756-L72SXT to 1756-L73SXT.
Description of Access the Module Object Feature 33
Guidelines for Program Parameters 51
Comparison of Program Parameters and Add-On Instructions 52
Network Address Translation (NAT) 89
3
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Rockwell Automation Publication 1756-RM094I-EN-P - September 2015 5
Summary of Changes
Notes:
6 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
Table of Contents
Preface
Logix5000 Controller Resources
Logic Execution
Additional Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Websites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Chapter 1
Estimate Memory Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
RSLinx Software Use of Logix5000 Controller Memory . . . . . . . . . 16
Compare PLC/SLC MEMORY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Controller Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Determine Total Connection Requirements . . . . . . . . . . . . . . . . . . . . . . . 18
CIP Sync . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Controller Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Chapter 2
Decide When to Use Tasks, Programs, and Routines . . . . . . . . . . . . . . . . 24
Specify Task Priorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Manage User Tasks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Considerations that Affect Task Execution. . . . . . . . . . . . . . . . . . . . . . . . . 27
Configure a Continuous Task. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Configure a Periodic Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Configure an Event Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Guidelines to Configure an Event Task. . . . . . . . . . . . . . . . . . . . . . . . . 30
Additional Considerations for Periodic and Event Tasks. . . . . . . . . 30
Select a System Overhead Percentage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Manage the System Overhead Timeslice Percentage. . . . . . . . . . . . . . . . . 32
Access the Module Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Create the Add-On Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Develop Application Code in Routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Comparison of Programming Languages . . . . . . . . . . . . . . . . . . . . . . . 34
Programming Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Inline Duplication. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Indexed Routine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Buffered Routine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Controller Prescan of Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Add-On Instruction Prescan Logic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Controller Postscan of SFC Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Add-On Instruction Postscan Logic. . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Timer Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
SFC Step Timer Execution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Edit an SFC Online . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Modular Programming Techniques
Chapter 3
Guidelines for Code Reuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Naming Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Parameter Name Prefixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
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Rockwell Automation Publication 1756-RM094I-EN-P - September 2015 7
Table of Contents
Guidelines to for Subroutines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Guidelines for User-defined Data Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Naming Conventions for User-Defined Data Types . . . . . . . . . . . . . 46
UDT Member Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Guidelines for Add-On Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Add-On Instruction Design Concepts. . . . . . . . . . . . . . . . . . . . . . . . . . 49
Naming Conventions for Add-On Instructions . . . . . . . . . . . . . . . . . 49
Comparison of Subroutines and Add-On Instructions . . . . . . . . . . . 49
Comparison of Partial Import/Export and Add-On Instructions . 50
Guidelines for Program Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Comparison of Program Parameters and Add-On Instructions . . . 52
Chapter 4
Address Data
Produced and Consumed Data
Guidelines for Data Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Guidelines for Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Indirect Addresses of Arrays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Guidelines for Array Indexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Guidelines for User-defined Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Select a Data Type for Bit Tags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Serial Bit Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Guidelines for String Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
PLC-5/SLC 500 Access of Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Configure Tags. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Guidelines for Base Tags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Create Alias Tags. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Guidelines for Data Scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Guidelines for Tag Names. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Guidelines for Extended Tag Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Tag Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Protect Data Access Control at Tag Level . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Chapter 5
Guidelines for Produced and Consumed Tags . . . . . . . . . . . . . . . . . . . . . . 67
Guidelines to Specify an RPI Rate for
Produced and Consumed Tags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Guidelines to Manage Connections for
Produced and Consumed Tags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Configure an Event Task Based on a Consumed Tag . . . . . . . . . . . . . . . . 69
Compare Messages and Produced/Consumed Tags . . . . . . . . . . . . . . . . . 70
Chapter 6
Communicate with I/O
8 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
Buffer I/O Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Guidelines to Specify an RPI Rate for I/O Modules . . . . . . . . . . . . . . . . . 72
Communication Formats for I/O Modules . . . . . . . . . . . . . . . . . . . . . . . . . 73
Electronic Keying. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Table of Contents
More Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Guidelines to Manage I/O Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Control 1771 I/O Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Communicate with HART Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Communicate with FOUNDATION Fieldbus Devices . . . . . . . . . . . . . 79
Create Tags for I/O Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Controller Ownership. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Runtime/Online Addition of Modules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Add Modules at Runtime/Online . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Design Considerations for Runtime/Online Addition
of Modules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Chapter 7
Determine the Appropriate Network
Communicate with Other Devices
EtherNet/IP Network Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Guidelines for EtherNet/IP Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Guidelines for Switches in EtherNet/IP Systems . . . . . . . . . . . . . . . . . . . . 90
Determine Whether Your System Operates Properly . . . . . . . . . . . . 90
Stratix Industrial Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
ControlNet Network Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Guidelines for ControlNet Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Guidelines for Unscheduled ControlNet Networks . . . . . . . . . . . . . . . . . 93
Compare Scheduled and Unscheduled ControlNet Communication . 94
DeviceNet Network Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Guidelines for DeviceNet Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Chapter 8
Cache Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Message Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Outgoing Unconnected Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Guidelines for Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Guidelines to Manage Message Connections . . . . . . . . . . . . . . . . . . . . . . 100
Guidelines for Block Transfer Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Map Tags. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
FactoryTalk Alarms and Events
System
Chapter 9
Guidelines for Logix-based Alarm Instructions . . . . . . . . . . . . . . . . . . . . 103
Changes in Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Configure Logix-based Alarm Instructions . . . . . . . . . . . . . . . . . . . . . . . . 105
Multiple Language Versions of Alarm Messages . . . . . . . . . . . . . . . . 106
Alarm Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Alarm Log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Programmatically Access Alarm Information . . . . . . . . . . . . . . . . . . . . . . 108
Shelve, Suppress, or Disable Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
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Rockwell Automation Publication 1756-RM094I-EN-P - September 2015 9
Table of Contents
Chapter 10
Optimize an Application for Use with
HMI
Develop Equipment Phases
Manage Firmware
Glossary
HMI Implementation Option. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Compare FactoryTalk View Site Edition and RSView32 Software . . . 112
Guidelines for FactoryTalk View Software. . . . . . . . . . . . . . . . . . . . . . . . . 112
How RSLinx Software Communicates with Logix5000 Controllers . 113
Compare RSLinx Classic and RSLinx Enterprise Software . . . . . . . . . . 114
Guidelines for RSLinx Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Guidelines to Configure Controller Tags . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Reference Controller Data from FactoryTalk View Software . . . . 115
Chapter 11
Guidelines for Equipment Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Equipment Phase Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Chapter 12
Guidelines to Manage Controller Firmware . . . . . . . . . . . . . . . . . . . . . . . 119
Compare Firmware Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Guidelines for the Firmware Supervisor . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Access Firmware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Index
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
10 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
Preface
Additional Resources
Resource Description
• EtherNet/IP Modules in Logix5000 Control Systems User Manual, ENET-UM001
• ControlNet Modules in Logix5000 Control Systems User Manual, CNET-UM001
• DeviceNet Modules in Logix5000 Control Systems User Manual, DNET-UM004
• Logix5000 Common Procedures Programming Manual, 1756-PM001
• Logix5000 Controllers General Instructions Reference Manual, 1756-RM003
• Logix5000 Controllers Process Control and Drives Instructions Reference Manual, 1756-RM006
• PhaseManager User Manual, LOGIX-UM001
• Logix5000 Controllers Motion Instructions Reference Manual, MOTION-RM002
• Logix5000 Controllers Import/Export Reference Manual, 1756-RM084
• ControlLogix System User Manual, 1756-UM001
• Motion Configuration and Startup User Manual, MOTION-UM001
• Motion Coordinate System User Manual, MOTION-UM002
• CompactLogix 5370 Controllers User Manual, 1769-UM021
• 1768 CompactLogix System User Manual, 1768-UM001
• 1769 CompactLogix System User Manual, 1769-UM011
• 1769 Packaged CompactLogix Controllers Quick Start and User Manual, IASIMP-QS010
• SoftLogix System User Manual, 1789-UM002
These documents contain additional information about Logix5000 controllers.
Networks
Logix5000 Controllers
ControlLogix Controllers
CompactLogix Controllers
SoftLogix Controllers
You can view or download publications at
http://www.rockwellautomation.com/literature/
. To order paper copies of
technical documentation, contact your local Allen-Bradley distributor or
Rockwell Automation sales representative.
Websites
Resource Description
http://www.ab.com/logix/ Logix Product Information
http://www.ab.com/networks/
http://www.rockwellautomation.com/support/
In the left pane under Downloads, selec t Software U pdates.
Http://www.rockwellautomation.com/support
In the left pane under Downloads, select Firmware Updates.
http://www.ab.com/networks/eds/
http://samplecode.rockwellautomation.com Studio 5000® Sample Code
Network Product Information
Software Updates
(produc t serial nu mber required)
Firmware Updates
(produc t serial nu mber required)
Rockwell Automation® EDS Files
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Preface
Notes:
12 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
Logix5000 Controller Resources
Logic and Data Memory
Logix
CPU
Backplane CPU
I/O Memory
Program source code
Tag data
RSLinx® tag group lists
I/O data
I/O force tables
Message buffers
Produced/consumed tags
1756-L7x ControlLogix controllers - Memory is separated into isolated sections.
Project Documentation Memor y
Comment descriptions
Alarm log
Extended tag properties
Logic and Data Memory
Logix
CPU
Backplane CPU
I/O Memory
Program source code
Tag data
RSLinx tag group lists
I/O data
I/O force tables
Message buffers
Produced/consumed tags
1768 CompactLogix and 1756-L6x ControlLogix controllers - Memory is separated into isolated sections.
TIP
Top ic Pag e
Estimate Memory Use 16
Controller Connections 17
Determine Total Connection Requirements 18
CIP Sync 20
Controller Mode 21
Chapter 1
The Logix CPU executes application code and messages. The backplane CPU
transfers I/O memory and other module data on the backplane. This CPU
operates independently from the Logix CPU, so it sends and receives I/O
information asynchronous to program execution.
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CPU usage is based on the number of devices in the I/O tree. About 6% of the
L7x CPU is used for every 100 devices in the I/O tree.
Chapter 1 Logix5000 Controller Resources
I/O Memory
Program source code
Tag data
RSLinx tag group lists
I/O data
I/O force tables
Message buffers
Produced/consumed tags
CompactLogix 5370 controllers - Memory is separated into isolated segments.
Logix
CPU
Logic and Data Memory
Comment descriptions
Alarm log
Extended tag properties
Project Documentation Memory
Logic, Data, and I/O Memory
Logix
CPU
Program source code
Tag data
RSLinx tag group lists
I/O data
I/O force tables
Message buffers
Produced/consumed tags
I/O task Comms task
1769 CompactLogix controllers - Memory is in one, contiguous section.
The Logix CPU executes application code and messages.
Controller I/O Task Priority Communication Task Priority
CompactLogix 5370 6 12
These controllers have one CPU that performs all operations. Isolated tasks
perform I/O and communication and interact with networks. These tasks
simulate the backplane CPU.
Controller I/O Task Priority Communication Task Priority
1769 CompactLogix 6 12
14 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
Logix5000 Controller Resources Chapter 1
Logic, Data, and I/O Memory
Logix
CPU
Program source code
Tag dat a
RSLinx tag group lists
I/O data
I/O force tables
Message buffers
Produced/consumed tags
SoftLogix controllers - Memory is in one, contiguous section.
Windows
operating
system
Project Documentation Memory
Comment descriptions
Alarm log
Extended tag properties
The SoftLogix controller has one CPU that works with the Windows operating
system to perform all operations. Rather than using controller priority levels for
I/O and communication tasks, the SoftLogix controller uses Windows priority
levels for these tasks.
Controller I/O Task Priority Communication Task Priority
SoftLogix Windows priority 16
(Idle)
Windows priority 16 (Idle)
For all controllers, memory is used at runtime for the following:
• Message processing
• RSLinx data handling to store tag groups
• Online edits to store edit rungs
• Graphical trends to buffer data
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Chapter 1 Logix5000 Controller Resources
IMPORTANT
IMPORTANT
Estimate Memory Use
Controller tasks _____ * 4,000 = _____ bytes (minimum 1 needed)
Digital I/O points _____ * 400 = _____ bytes
Analog I/O points _____ * 2,600 = _____ bytes
DeviceNet modules
Other communication modules
Motion axis _____ * 8,000 = _____ bytes
FactoryTalk® alarm instruction _____ * 2,200 = _____ bytes (per alarm)
FactoryTalk subscriber _____ * 2,000 = _____ bytes (per subscriber)
1
The first DeviceNet module is 7400 bytes. Additional DeviceNet modules are 5800 bytes each.
2
Count all communication modules in the system, not just the modules in the local chassis. The count includes device connection modules, adapters, and ports on
PanelView™ terminals.
The equations provide an estimate of the memory that is needed for a controller.
If you configure controllers for redundancy, you must double the memory
resources that are required for a non-redundant application.
1
_____ * 7,400 = _____ bytes
2
_____ * 2,000 = _____ bytes
To t a l = _____ bytes
Reserve 20…30% of the controller memory to accommodate growth.
RSLinx Software Use of Logix5000 Controller Memory
The amount of memory that RSLinx software needs depends on the type of data
RSLinx software reads. These equations provide a memory estimate.
RSLinx overhead
(per connection) _____ * 1345 = ___ bytes (four connections by default)
Individual tags _____ * 45 = ___ bytes
Arrays / structures _____ * 7 = ___ bytes
To t a l =___bytes
You can consolidate tags into an array or a structure to reduce the communication
overhead and the number of connections that are used to obtain the data.
16 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
Logix5000 Controller Resources Chapter 1
Compare PLC/SLC MEMORY
The Logix5000 controllers use compiled instructions to provide faster execution
times than PLC or SLC™ processors. The compiled instructions use more
memory when compared to the instructions in PLC and SLC processors.
If you have a PLC/SLC program, you can estimate the number of bytes it takes in
a Logix5000 controller by the following equation:
number PLC/SLC words 18 = number of Logix5000 bytes
Controller Connections
Communication Attribute 1756-L7x ControlLogix 1756-L6x ControlLogix
Connections 500 250 100 256 250
Cached messages
Unconnected receive buffers 3
Unconnected transmit buffers Default 20 (can be increased to 40) Default 10 (can be increased to 40)
(1)
32 for messages and block transfers combined
A Logix5000 controller uses a connection to establish a communication link
between two devices. Connections can be made to the following:
• Controller to local I/O modules or local communication modules
• Controller to remote I/O or remote communication modules
• Controller to remote I/O (rack optimized) modules
For more information on connections for I/O, see Communicate with I/O
on page 71.
• Produced and consumed tags
For more information, see Produced and Consumed Data
• Messages
For more information, see Communicate with I/O
• Access to RSLogix 5000® software
• RSLinx software access for HMI or other software applications
The controllers have different communication limits.
1769 CompactLogix CompactLogix 5370 1768 CompactLogix
and SoftLogix
on page 71.
on page 67.
(1) See Communicate with Other Devices on page 97 for more information about messages and buffers.
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Chapter 1 Logix5000 Controller Resources
The limit of connections can ultimately reside in the communication module you
use for the connection. If a message path routes through a communication
module, the connection that is related to the message also counts toward the
connection limit of that communication module.
Controller Communication Device Suppor ted Connections
ControlLogix 1756-CN2R, 1756-CN2RXT
100 CIP connections
(any combination of scheduled and message connections)
1756-CN2/B
1756-CNB,1756 -CNBR 64 CIP connections
1756-EN2F, 1756-EN2T, 1756-EN2TR, 1756EN2TXT, 1756-EN3TR
1756-ENBT
1756-EWEB
1768 CompactLogix 1768-ENBT
1768-EWEB
1769 CompactLogix 1769-L32C, 1769-L35CR 32 CIP connections
1769-L32E, 1769-L35E 32 CIP connections
1769-L23Ex 32 CIP connections
CompactLogix 5370 Built-in Ethernet ports See the CompactLogix 5370 Controllers User Manual, publication 1769-UM021
SoftLogix 5800 1784-PCICS 128 CIP connections
128 CIP connections
depending on RPI, recommend that you use only 48 connections
(any combination of scheduled and message connections)
256 CIP connections
128 TCP/IP connections
128 CIP connections
64 TCP/IP connections
64 CIP connections
32 TCP/IP connections
depending on RPI, as many as 22 connections can be scheduled
The remaining connections (or all 32, if you have no scheduled connections) can
be used for message connections
64 TCP/IP connections
12 TCP/IP connections
for information on how to count EtherNet/IP nodes on the I/O Configuration
section of RSLogix 5000 software.
127 can be scheduled connections
,
Determine Total Connection Requirements
The total connections for a Logix5000 controller include both local and remote
connections. Counting local connections is not an issue for CompactLogix
controllers. They support the maximum number of modules that are permitted
in their systems.
When designing your CompactLogix 5370 controllers, you must consider these
resources:
• EtherNet/IP network nodes
• Controller connections
For more information, see the CompactLogix 5370 Controllers User Manual,
publication 1769-UM021
18 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
.
Logix5000 Controller Resources Chapter 1
IMPORTANT
The ControlLogix and SoftLogix controllers support more communication
modules than the other controllers, so you must tally local connections to make
sure that you stay within the connection limit.
Use this table to tally local connections.
Connection Type Device Quantity x Connections per Module = Total Connections
Local I/O module (always a direct connection) x 1 =
SERCOS Motion module x 3 =
ControlNet communication module x 0 =
EtherNet/IP communication module x 0 =
DeviceNet communication module x 2 =
DH+/Remote I/O communication module x 1 =
DH-485 communication module x 1 =
RSLogix 5000 software access to controller x 1 =
Tot a l
A redundant system uses eight connections in the controller.
The communication modules that you select determine how many remote
connections are available. Use this table to tally remote connections.
Connection Type Device Quantity x Connections per Module = Total Connections
Remote ControlNet communication module
Configured as a direct (none) connection
Configured as a rack-optimized connection
Remote EtherNet/IP communication module
Configured as a direct (none) connection
Configured as a rack-optimized connection
Remote device over a DeviceNet network
(accounted for in rack-optimized connection for local DeviceNet module)
Safety device on a DeviceNet or EtherNet/IP network x 2 =
Other remote communication adapter x 1 =
Distributed I/O module (individually configured for a direct connection) x 1 =
Produced tag and first consumer
Each additional consumer
Consumed ta g x 1 =
Connected message (CIP Data Table Read/Write and DH+) x 1 =
Block transfer message x 1 =
RSLinx software access for HMI or other software applications x 4 =
RSLinx® Enterprise software for HMI or other software applications x 5 =
Tot a l
x
0 or
1
x
0 or
1
x0=
x21=
=
=
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Chapter 1 Logix5000 Controller Resources
CIP Sync
CIP Sync is a time synchronization implementation that incorporates
IEEE-1588 standards on the EtherNet/IP protocol. CIP Sync provides the
control system access to synchronization information and transport and routing
of a system clock on standard CIP networks.
CIP Sync offers the following features:
• Precision Time Protocol (PTP)
• Nanosecond resolution +/- 100 nanosecond synchronization (hardware
assist clock)
• Master clock reference
• No longer need application code or software to synchronize clocks
between controller, HMI, and other control hardware.
• Open standard lets compatibility with most IEEE-1588 v2 products exist,
letting the integration with GPS and other IT layer devices occur.
• Alarm system automatically picks up time stamps from CIP Sync system
time
• System self-heals, so that if one clock master fails the rest arbitrate to find
the next best clock master.
A ControlLogix controller or 1756-EN2T can become a system clock master.
Other Logix5000 controllers can require application code.
The controller or networked device that wins system clock arbitration is the
Grandmaster clock. The wall clock time can only be set from the system Grand
Master device. If you adjust a controller clock, the controller could reject that
time if it is not or does not become the Grandmaster clock.
You can configure the system clock via RSLogix 5000 software, version 18 and
later, and programmatically via GSV/SSV instructions. Use a GSV/SSV
instruction with the Time Sync object to do the following:
• Enable or disable CIP Sync
• Get or set the time
• Set priority to override other masters
• Get synchronization status
• Get current PTP master status and state information
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Logix5000 Controller Resources Chapter 1
IMPORTANT
Controller Mode
The controller mode switch provides a mechanical means to enhance controller
and control system security. You must physically move the switch to change the
operating mode from RUN to REM or to PROG.
Remote lets you change the operational mode to REM RUN or REM PROG via
RSLogix 5000 software.
During runtime, we recommend that you place the controller mode switch in
RUN mode and remove the key (if applicable) from the switch. This practice
helps discourage unauthorized access to the controller or potential tampering
with the controller program, configuration, or device firmware. Place the mode
switch in REM or PROG mode during controller commissioning, maintenance,
and whenever temporary access is necessary to change the program,
configuration, or firmware.
For more information on controller mode switches, see the ControlLogix System
User Manual, publication 1756-UM001
.
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Chapter 1 Logix5000 Controller Resources
Notes:
22 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
Logic Execution
Tasks to configure controller execution
Programs to group data and logic
Top ic Pag e
Decide When to Use Tasks, Programs, and Routines 24
Specify Task Priorities 25
Manage User Tasks 26
Considerations that Affect Task Execution 27
Configure a Co ntinuous Task 29
Configure a Periodic Task 29
Configure an Event Task 30
Select a System Overhead Percentage 31
Manage the System Overhead Timeslice Percentage 32
Access the Module Object 33
Develop Application Code in Routines 34
Programming Methods 35
Controller Prescan of Logic 36
Controller Postscan of SFC Logic 37
Timer Exe cution 3 8
Edit an S FC Online 39
Chapter 2
The controller operating system is a ct2000LAK pre-emptive multitasking
system that is IEC 61131-3 compliant.
A task provides scheduling and priority information for a set of one or more
programs. You can configure tasks as either continuous, periodic, or event.
A task contains programs, each with its own routines and program-scoped tags.
Once a task is triggered (activated), the programs that are assigned to the task
execute in the order in which they are listed in the Controller Organizer.
Programs are useful for projects that multiple programmers develop. During
development, the code in one program that uses program-scoped tags can be
duplicated in a second program to minimize the possibility of tag
names colliding.
With firmware revision 15, tasks can contain programs and equipment phases.
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Chapter 2 Logic Execu tion
Routines to encapsulate
executable code that is written
in one programming language
Routines contain the executable code. Each program has a main routine that is
the first routine to execute within a program. Use logic, such as the Jump to
Subroutine (JSR) instruction, to call other routines. You can also specify an
optional program fault routine.
See Develop Application Code in Routines
on page 34 for information on
selecting programming languages, and how the controller prescans and
postscans logic.
Decide When to Use Tasks,
Use these considerations to determine when to use a task, program, or routine.
Programs, and Routines
Comparison Task Program and Equipment Phase Routine
Quantity available Varies by controller (4, 6, 8, or 32) 32 program and equipment phases
Function Determines how and when code is executed Organizes groups of routines that share a
Use • Most code is expected to reside in a
continuous task
• Use a periodic task for slower processes or
when time-based operation is critical
• Use an event task for operations that
require synchronization to a specific event
Considerations • A high number of tasks can be difficult to
debug
• Can disable output processing on some
tasks to improve performance
• Tasks can be inhibited to prevent execution
• Do not configure multiple tasks at the same
priority
(combined) per task
(100 for ControlLogix and SoftLogix
controllers)
common data area and function.
• Put major equipment pieces or plant cells
into isolated programs
• Use programs to isolate different
programmers or create reusable code
• Configurable execution order within a task
• Isolate individual batch phases or discrete
machine operations
• Data spanning multiple programs must go
into controller-scoped area
• Listed in the Controller Organizer in the
order of execution
Unlimited number of routines per program
Contains executable code (relay ladder,
function block diagram, sequential function
chart, or structured text)
• Isolate machine or cell functions in a
• Use the appropriate language for the
• Modularize code into subroutines that can
• Subroutines with multiple calls can be
• Data can be referenced from program-
• Calling many routines impacts scan time
• Listed in the Controller Organizer as Main,
routin e
process
be called multiple times
difficult to debug
scoped and controller-scoped areas
Fault, and then alphabetically
For more information about equipment phases, see Develop Equipment Phases
on page 117.
24 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
Logic Execution Chapter 2
Specify Task Priorities
Each task in the controller has a priority level. A higher priority task (such as 1)
interrupts any lower priority task (such as 15). The continuous task has the
lowest priority; periodic or event tasks always interrupt continuous tasks.
Logix5000 Controller User Tasks Supported Available Priority Levels
ControlLogix 32 15
CompactLogix 5370 32 15
1768-L43, 1769-L45 CompactLogix 16 15
1769-L35CR, 1769-L35E CompactLogix 8 15
1769-L32C,1769-L32E CompactLogix 6 15
1769-L31 CompactLogix 4 15
1769-L23E-QB1B, 1769-L23E-QBFC1B, 1769-L23-QBFC1B
Compac tLogix
SoftLogix 5800 32 3
315
The Logix5000 controller has these types of tasks.
Priority User Task Description
Highest
Lowest
N/A CPU overhead - serial port and general CPU operations
N/A Motion planner - executed at coarse update rate
N/A Safety task - safety logic
N/A Redundancy task - communication in redundant systems
N/A Trend data collection - high-speed collection of trend data values
Priority 1 Event/Periodic User defined
Priority 2 Event/Periodic User defined
Priority 3 Event/Periodic User defined
Priority 4 Event/Periodic User defined
Priority 5 Event/Periodic User defined
Priority 6 Event/Periodic User defined
1769 CompactLogix controllers process I/O as a periodic task based on the chassis RPI setting
Priority 7 Event/Periodic User defined
Priority 8 Event/Periodic User defined
Priority 9 Event/Periodic User defined
Priority 10 Event/Periodic User defined
Priority 11 Event/Periodic User defined
Priority 12 Event/Periodic User defined
CompactLogix communication and scheduled connection maintenance
Priority 13 Event/Periodic User defined
Priority 14 Event/Periodic User defined
Priority 15 Event/Periodic User defined
Continuous Message handler - based on system overhead timeslice
If a periodic or event task is executing when another is triggered, and both tasks
are at the same priority level, the tasks’ timeslice executes in 1 ms increments until
one of the tasks completes execution.
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Chapter 2 Logic Execu tion
Manage User Tasks
If you want logic to execute Use this task Description
All of the time Continuous task The continuous task runs in the background. Any CPU time that is not allocated to other operations or
• At a constant period (such as every 100 ms)
• Multiple times within the scan of your other logic
Immediately when an event occurs Event task An event task performs a function only when a specific event (trigger) occurs. Whenever the trigger for
You can configure these user tasks.
tasks is used to execute the continuous task.
• The continuous task runs all of 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.
Periodic task A periodic task performs a function at a specific time interval. Whenever the time for the periodic task
expires, the periodic task:
• Interrupts any lower priority tasks.
• Executes one time.
• Returns control to where the previous task left off.
the event task occurs, the event task:
• Interrupts any lower priority tasks.
• Executes one time.
• Returns control to where the previous task left off.
See Configure an Event Task
do not support all triggers.
on page 30 for the triggers for an event task. Some Logix5000 controllers
The user tasks that you create appear in the Tasks folder of the controller. The
predefined system tasks do not appear in the Tasks folder and they do not count
toward the task limit of the controller:
• Motion planner
• I/O processing
• System overhead
• Output processing
26 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
Logic Execution Chapter 2
Considerations that Affect Task Execution
Consideration Description
Motion planner The motion planner interrupts all other tasks, regardless of their priority.
I/O processing CompactLogix and SoftLogix controllers use a dedicated periodic task to process I/O data. This I/O task:
System overhead
See also Select a System Overhead Percentage on page 31.
Output processing At the end of a task, the controller performs output processing for the output modules in your system. This
Too many tasks If you have too many tasks, then the following can occur:
• 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.
• CompactLogix controllers, operates at priority 6.
SoftLogix controllers, operates at Windows priority 16 (Idle).
• Higher-priority tasks take precedence over the I/O task and can affect processing.
• Executes at the fastest RPI you have scheduled for the system.
• Executes for as long as it takes to scan the configured I/O modules.
System overhead is the time that the controller spends on message communication and background tasks.
• Message communication is any communication that you do not configure through the I/O configuration folder
of the project, such as MSG instructions.
• Message communication occurs only when a periodic or event task is not running. If you use multiple tasks, make
sure that their scan times and execution intervals leave enough time for message communication.
• System overhead interrupts only the continuous task.
• The system overhead timeslice specifies the percentage of time (excluding the time for periodic or event tasks)
that the controller devotes to message communication.
• The controller performs message communication for up to 1 ms at a time and then resumes the continuous task.
• Adjust the update rates of the tasks as needed to get the best trade-off between executing your logic and
servicing message communic ation.
processing depends on the number of output connections that are configured in the I/O tree.
• Continuous task can take too long to complete.
• Other tasks can experience overlaps. If a task is interrupted too frequently or too long, it must be triggered again
to complete its execution.
• Controller communication can be slower.
• If your application is designed for data collection, try to avoid multiple tasks.
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Chapter 2 Logic Execu tion
1 2 4 5 63
1
2
3
4
5
6
This example depicts the execution of a project with these tasks.
Task Priority Period Execution Time Duration
Motion planner N/A 8 ms (course update rate) 1 ms 1 ms
Event task 1 1 N/A 1 ms 1
Periodic task 1 2 12 ms 2 ms 24ms
I/O task—N/A to ControlLogix and SoftLogix controllers 7 5 ms (fastest RPI) 1 ms 15 ms
System overhead N/A Timeslice = 20% 1 ms 1
Continuous task N/A N/A 20 ms 48 ms
2 ms
6 ms
Motion
Planner
Event Task 1
Peri odic
Tas k 1
I/O Task
System
Overhead
Continuous
Tas k
Legend :
Description
Task executes. Task is interrupted (suspended).
5 101520253035404550
Initially, the controller executes the motion planner and the I/O task (if one exists).
After executing 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 executing the continuous task again for 4 ms, the controller triggers the system overhead.
The triggers occur for event task 1.
Event task 1 waits until the motion planner is done.
Lower priority tasks experience longer delays.
The continuous task automatically restarts.
28 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
Logic Execution Chapter 2
Configure a Continuous Task
The continuous task is created automatically when you open an RSLogix 5000®
software project. A continuous task is similar to how logic executes on PLC-5®
and SLC™ 500 processors. A Logix5000 controller supports one continuous task,
but a continuous task is not required. You can configure whether the task updates
output modules at the end of the continuous task. You can change the continuous
task to either a periodic or event task.
The CPU timeslices between the continuous task and system overhead. Each
task switch between user task and system overhead takes more CPU time to load
and restore task information.
RSLogix 5000 software, version 16 and later, forces at least 1 ms of execution
time for the continuous task, regardless of the system overhead timeslice. This
more efficiently uses system resources because letting shorter execution times of
the continuous task exist means switching tasks more frequently.
System Overhead Timeslice % Communication Execution (msec) Continuous Task Execution (msec)
10 1 9
20 1 4
33 1 2
50 1 1
66 2 1
80 4 1
90 9 1
Configure a Periodic Task
A periodic task executes automatically based on a preconfigured interval. This
task is similar to selectable timed interrupts in PLC-5® and SLC 500 processors.
You can configure whether the task updates output modules at the end of the
periodic task. After the task executes, it does not execute again until the
configured time interval has elapsed.
If your application has a lot of communication, such as RSLinx communication,
use a periodic task rather than a continuous task.
AB Drives
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Chapter 2 Logic Execu tion
Configure an Event Task
An event task executes automatically based on a trigger event occurring or if a
trigger event does not occur in a specific time interval. You configure whether the
task updates output modules at the end of the task. After the task executes, it
does not execute again until the event occurs again. Each event task requires a
specific trigger.
Trigger Description
Module Input Data State Change With Logix5000 controllers, a remote input module (digital or analog) triggers an event task that is based on the change of state (COS)
Consumed Tag Only one consumed tag can trigger a specific event task. Use an IoT instruction in the producing controller to signal the production of
Axis Registration 1or 2 A registration input triggers the event task.
Axis Watch A watch position triggers the event task.
Motion Group Execution The coarse update period for the motion group triggers the execution of both the motion planner and the event task. Because the motion
EVENT Instruction Multiple EVENT instructions can trigger the same task.
configuration for the module. Enable COS for only one point on the module. If you enable COS for multiple points, a task overlap of the event
task can occur.
• The ControlLogix sequence of events modules (1756-IB16ISOE, 1756-IH16ISOE) use the Enable CST Capture feature instead of COS.
• The embedded input points on the 1769-L16ER-BB1B, 1769-L18ER-BB1B, and 1769-L18ERM-BB1B modules can be configured to trigger
an event task when a COS occurs.
new data.
planner interrupts all other tasks, it executes first.
For more information on event tasks, see:
• Logix5000 Controllers Common Procedures Programming Manual,
publication 1756-PM001
• Using Event Tasks with Logix5000 Controllers,
publication LOGIX-WP003
Guidelines to Configure an Event Task
Guideline Description
Place the I/O module being used to trigger an event in the
same chassis as the controller.
Limit events on digital inputs to one input bit on a module. All inputs on a module trigger one event, so if you use multiple bits you increase the chance of a task overlap. Configure
Set the priority of the event task as the highest priority on
the controller.
Limit the number of event tasks. Increasing the number of event tasks reduces the available CPU bandwidth and increases the chances of task overlap.
Placing the I/O module in a remote chassis adds more network communication and processing to the response time.
the module to detect change of state on the trigger input and turn off the other bits.
If the priority of the event task is lower than a periodic task, the event task has to wait for the periodic task to com plete
execution .
Additional Considerations for Periodic and Event Tasks
Consideration Description
Amount of code in the event task Each logic element (for example, rung, instruction, or structured text construct) adds to scan time.
Task priority If the event task is not the highest priority task, a higher priority task can 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 executing task. (The task with the CPS or UID.)
Communication interrupts Incoming character processing through the serial port interrupts a task, regardless of the priority of the task.
Motion planner The motion planner takes precedence over event or periodic tasks
Trends Trend data collection takes precedence over event or periodic tasks.
Output processing You can disable output processing at the end of a task to reduce the amount of task processing time. As of RSLogix 5000 software, version 16,
the Controller Organizer displays whether outputs processing is disabled.
30 Rockwell Automation Publication 1756-RM094I-EN-P - September 2015
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