ang.
Logix5000
Controllers Design
Considerations
1756-Lx, 1769-Lx, 1789-Lx, 1794-Lx,
PowerFlex 700S
Reference Manual
embedded in PowerFlex 700S
•
•
•
•
panel mount
DIN rail
•
•
•
•
none
•
•
•
•
•
panel mount
DIN rail
•
•
•
•
1756-L55M12
1756-L55M13
1756-L55M15
1756-L55M16
1756-L55M22
1756-L55M23
1756-L55M24
1756-L6x
1 port RS-232 serial
(DF1 or ASCII)
EtherNet/IP
ControlNet
DeviceNet
Data Highway Plus
Universal Remote I/O
serial
Modbus via ladder routine
DH-485
SynchLink
SERCOS interface
analog interface
hydraulic interface
1756 chassis
•
•
•
•
built-in communication ports
communication options
(these options have specific
products and profiles for their
platform - other options are
available via 3rd party products and
generic profiles)
integrated motion support
mounting and /or
installation options
programming languages
relay ladder
structured text
function block
sequential function chart
none
none
none
none
yes
yes
yes
CompactFlash
relay ladder
structured text
function block
sequential function chart
not applicable
EtherNet/IP
DeviceNet
serial
Modbus via ladder routine
DH-485
•
•
1769-L20: 1 RS-232 serial port
(DF1 or ASCII)
1769-L3, -L31: 2 RS-232 serial
ports (one DF1 only,
other DF1 or ASCII)
1769-L32E, -L35E: 1 EtherNet/IP
port and 1 RS-232 serial port
(DF1 or ASCII)
yes
yes
CompactFlash
CompactFlash
CompactFlash
1769-L20
1769-L30
1769-L31
1769-L32E
1769-L35E
•
64 Kbytes
256 Kbytes
512 Kbytes
750 Kbytes
1.5 Mbytes
1769-L20
1769-L30
1769-L31
1769-L32E
1769-L35E
2 Mbytes
3 slots, no motion
64 Mbytes
5 slots
64 Mbytes
16 slots
relay ladder
structured text
function block
sequential function chart
external routines
SERCOS interface
analog interface
EtherNet/IP
ControlNet
DeviceNet
serial
depends on personal computer
none
1789-L60
1789-L30
1789-L10
1 RS-232 serial port
(DF1 or ASCII)
2 slots for 1788 communication
cards
yes
yes
64 Kbytes
512 Kbytes
relay ladder
structured text
function block
sequential function chart
not applicable
EtherNet/IP
ControlNet
DeviceNet
serial
Modbus via ladder routine
DH-485
•
•
1794-L33
1794-L34/B
1794-L33
1794-L34
1 RS-232 serial port
(DF1 or ASCII)
1 slot for 1788 communication cards
relay ladder
structured text
function block
sequential function chart
1 full servo
1 feedback axis
EtherNet/IP
ControlNet
DeviceNet
serial
Modbus via ladder routine
DH-485
•
•
yes (expansion memory)
256 Kbytes
768 Kbytes with expansion memory
8 tasks (only 1 continuous)
event tasks: supports axis and
motion event triggers
nonvolatile user memory
750 Kbytes
1.5 Mbytes
3.5 Mbytes
7.5 Mbytes
750 Kbytes
1.5 Mbytes
3.5Mbytes
2 Mbytes
4 Mbytes
8 Mbytes
•
•
1756-L55M12
1756-L55M13
1756-L55M15
1756-L55M16
1756-L55M22
1756-L55M23
1756-L55M24
1756-L61
1756-L62
1756-L63
8 tasks (only 1 continuous)
event tasks: supports consumed
tag trigger and EVENT
instruction
•
•
32 tasks (only 1 continuous)
event tasks: supports all event
triggers
•
•
user memory
1769-L35E: 8 tasks
1769-L32E: 6 tasks
1769-L31: 4 tasks
1769-L20, -L30: 4 tasks
only 1 task can be continuous
event tasks: supports consumed
tag trigger and EVENT
instruction
•
•
•
•
•
•
32 tasks (only 1 continuous)
event tasks: supports all event
triggers
•
•
PowerFlex 700S DriveLogix
controller tasks
• continuous
• periodic
• event
1794 FlexLogix
1789 SoftLogix5800
1769 CompactLogix
1756 ControlLogix
Common Characteristic:
Logix5000 Controllers Comparison
Preface
Designing Logix5000 Systems
Introduction
This reference manual provides guidelines you can follow to optimize
your system. This manual also provides system information you need
to make system design choices. As you read this manual:
This symbol:
Indicates:
guidelines you should follow
programming practices that can improve system performance
things you can do
considerations you should know when making design choices
system information that can affect system performance
things you should know
In addition to the controller-specific topics covered in each chapter,
the back of this manual includes a:
• glossary of commonly used terms
• list of related publications
This manual is meant for experienced Logix-system programmers. The
information in this manual is presented with the assumption that the
reader understands how to implement the guidelines. The list of
related publications at the back of the manual identifies resources you
can use for more details on how to implement the guidelines.
i
Publication 1756-RM094A-EN-P - May 2004
ii
Designing Logix5000 Systems
Important User Information
Solid state equipment has operational characteristics differing from those of
electromechanical equipment. Safety Guidelines for the Application,
Installation and Maintenance of Solid State Controls (Publication SGI-1.1
available from your local Rockwell Automation sales office or online at
http://www.ab.com/manuals/gi) describes some important differences
between solid state equipment and hard-wired electromechanical devices.
Because of this difference, and also because of the wide variety of uses for
solid state equipment, all persons responsible for applying this equipment
must satisfy themselves that each intended application of this equipment is
acceptable.
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 we use notes to make you aware of safety
considerations.
WARNING
IMPORTANT
ATTENTION
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.
Identifies information that is critical for successful
application and understanding of the product.
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
• recognize the consequence
Publication 1756-RM094A-EN-P - May 2004
SHOCK HAZARD
Labels may be located on or inside the drive to alert
people that dangerous voltage may be present.
BURN HAZARD
Labels may be located on or inside the drive to alert
people that surfaces may be dangerous temperatures.
Table of Contents
Chapter 1
Logix5000 Controller Resources
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Using Connections for Communications . . . . . . . . . . . . . . . . . . . . . . . . 1-3
Determining Total Connection Requirements. . . . . . . . . . . . . . . . . . . . . 1-5
Chapter 2
Dividing Logic into Tasks, Programs,
and Routines
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Deciding When to Use Tasks, Programs, and Routines. .
Specifying Task Priorities . . . . . . . . . . . . . . . . . . . . . . .
Managing User Tasks . . . . . . . . . . . . . . . . . . . . . . . . . .
Factors that Affect Task Execution . . . . . . . . . . . . . . . .
Configuring a Continuous Task. . . . . . . . . . . . . . . . . . .
Configuring a Periodic Task . . . . . . . . . . . . . . . . . . . . .
Configuring an Event Task . . . . . . . . . . . . . . . . . . . . . .
Guidelines for Configuring an Event Task . . . . . . . . . . .
Selecting a System Overhead Percentage. . . . . . . . . . . .
Managing the System Overhead Timeslice Percentage . .
Developing Application Code in Routines . . . . . . . . . . .
Programming Methods . . . . . . . . . . . . . . . . . . . . . . . . .
Controller Prescan of Logic. . . . . . . . . . . . . . . . . . . . . .
Controller Postscan of SFC Logic. . . . . . . . . . . . . . . . . .
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2-1
2-2
2-3
2-5
2-6
2-8
2-8
2-8
2-9
2-10
2-11
2-12
2-13
2-14
2-14
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3-1
3-2
3-3
3-4
3-5
3-6
3-6
3-7
3-8
3-9
3-10
3-10
3-11
3-12
3-13
3-13
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Guidelines for Creating Produced and Consumed Tags . . . . . . . . . . . . .
Guidelines for Specifying an RPI Rate . . . . . . . . . . . . . . . . . . . . . . . . . .
Guidelines for Managing Connections for Produced and Consumed Tags
Configuring an Event Task Based on a Consumed Tag . . . . . . . . . . . . .
Comparing Messages and Produced/Consumed Tags . . . . . . . . . . . . . . .
4-1
4-2
4-3
4-3
4-3
4-4
Chapter 3
Addressing Data
Introduction. . . . . . . . . . . . . . . . . . . .
Guidelines for Data Types . . . . . . . . .
Arrays . . . . . . . . . . . . . . . . . . . . . . . .
Guidelines for Arrays . . . . . . . . . . . . .
Indirect Addressing of Arrays . . . . . . .
Guidelines for Array Indexes . . . . . . .
Prescan of an Array Index . . . . . . . . .
Guidelines for User-Defined Structures
Selecting a Data Type for Bit Tags . . .
Serial Bit Addressing . . . . . . . . . . . . .
Guidelines for String Data Types. . . . .
PLC-5/SLC 500 Access of Strings . . . . .
Configuring Tags . . . . . . . . . . . . . . . .
Guidelines for Base Tags . . . . . . . . . .
Creating Alias Tags. . . . . . . . . . . . . . .
Guidelines for Data Scope . . . . . . . . .
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Chapter 4
Sharing Tag Data with Other Controllers
(Produced and Consumed Tags)
1
Publication 1756-RM094A-EN-P - May 2004
Table of Contents
2
Chapter 5
Designing Networks
Introduction. . . . . . . . . . . . . . .
Select a Network . . . . . . . . . . .
EtherNet/IP Network Topology.
Guidelines for EtherNet/IP . . . .
ControlNet Network Topology .
Guidelines for ControlNet. . . . .
DeviceNet Network Topology. .
Guidelines for DeviceNet . . . . .
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5-1
5-1
5-2
5-3
5-4
5-5
5-6
5-7
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6-1
6-1
6-2
6-3
6-4
6-5
6-6
6-7
Chapter 6
Communicating with I/O
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Buffering I/O Data . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Guidelines for Specifying an RPI Rate for I/O Modules .
Communication Formats for I/O Modules . . . . . . . . . . .
Guidelines for Managing I/O Connections. . . . . . . . . . .
Guidelines for Managing I/O Connections (continued) .
Creating Tags for I/O Data . . . . . . . . . . . . . . . . . . . . . .
Controller Ownership. . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 7
Communicating with Other Devices
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . .
Caching Messages . . . . . . . . . . . . . . . . . . . . . .
Message Buffers . . . . . . . . . . . . . . . . . . . . . . . .
Guidelines for Messages . . . . . . . . . . . . . . . . . .
Guidelines for Managing Message Connections .
Guidelines for Block-Transfer Messages . . . . . .
Mapping Tags . . . . . . . . . . . . . . . . . . . . . . . . .
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7-1
7-2
7-2
7-4
7-5
7-6
7-6
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8-1
8-1
8-2
8-2
8-3
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Guidelines for HMI Applications . . . . . . . . . . . . . . . . . . . . . . . . .
Comparison of RSView32 and RSView Enterprise . . . . . . . . . . . .
How RSLinx Software Communicates with Logix5000 Controllers .
Guidelines for RSLinx Software . . . . . . . . . . . . . . . . . . . . . . . . . .
Comparison of RSLinx Classic and RSLinx Enterprise . . . . . . . . . .
Guidelines for Configuring Controller Tags . . . . . . . . . . . . . . . . .
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9-1
9-2
9-2
9-3
9-4
9-5
9-6
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10-1
10-1
10-2
10-3
10-3
Chapter 8
Optimizing an Application for Motion
Control
Introduction. . . . . . . . . . . .
Coarse Update Rate . . . . . .
Axis Limits . . . . . . . . . . . . .
Performance Limits. . . . . . .
Motion Event Task Triggers
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Chapter 9
Optimizing an Application for Use with
HMI
Chapter 10
Optimizing an Application for Process
Control
Publication 1756-RM094A-EN-P - May 2004
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Comparison of PID and PIDE Instructions . . . . . . . . . . .
Guidelines for Programming PID Loops . . . . . . . . . . . .
Advanced Process Instructions . . . . . . . . . . . . . . . . . . .
Faceplates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Chapter
1
Logix5000 Controller Resources
Introduction
Depending on the controller, resources are divided differently:
ControlLogix controllers - memory is separated into two, isolated sections
Logic and Data Memory
I/O Memory
I/O data
program source code
Logix
CPU
tag data
Backplane
CPU
I/O force tables
message buffers
RSLinx tag group lists
produced/consumed tags
• The Logix CPU executes application code and messages.
• The backplane CPU communicates with I/O and sends/receives
data from the backplane. This CPU operates independently from
the Logix CPU, so it sends and receives I/O information
asynchronous to program execution.
CompactLogix, FlexLogix, and DriveLogix controllers - memory is in one, contiguous section
Logic, Data, and I/O Memory
program source code
I/O data
tag data
I/O force tables
RSLinx tag group lists
message buffers
Logix
CPU
I/O task
comms
task
produced/consumed
These controllers have a single CPU that performs all operations.
Isolated tasks perform I/O and communications and interact with
networks. These tasks simulate the backplane CPU.
For this controller:
CompactLogix, FlexLogix, and DriveLogix
1
The I/O task is priority:
6
The communications task is priority:
12
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Logix5000 Controller Resources
SoftLogix controllers - memory is in one, contiguous section
Logic, Data, and I/O Memory
program source code
I/O data
tag data
I/O force tables
RSLinx tag group lists
message buffers
Logix
CPU
Windows
operating
system
produced/consumed
The SoftLogix controller has a single CPU that works in conjunction
with the Windows operating system to perform all operations. Rather
than using controller priority levels for I/O and communications tasks,
the SoftLogix controller uses Windows priority levels for these tasks.
For this controller:
The I/O task is:
The communications task is:
SoftLogix
Windows priority 16 (Idle)
Windows priority 16 (Idle)
For all controllers, memory is used at run time for:
• message processing to buffer incoming and outgoing messages
• RSLinx data handling to store tag groups
• online edits to store edit rungs
• graphical trends to buffer data
Estimating memory use
The following equations provide an estimate of the memory needed
for a controller.
Controller tasks
_____ * 4000 =
_____ bytes (minimum 1 needed)
Discrete I/O points
_____ * 400
=
_____ bytes
Analog I/O points
_____ * 2600 =
_____ bytes
DeviceNet modules1
_____ * 7400 =
_____ bytes
Other communication modules2_____ * 2000 =
_____ bytes
Motion axis
_____ * 8000 =
_____ bytes
Total =
_____ bytes
1
The first DeviceNet module is 7400 bytes. Additional DeviceNet modules are 5800 bytes each.
2Count all the communication modules in the system, not just those in the local chassis. This includes device
connection modules, adapter modules, and ports on PanelView terminals.
Reserve 20-30% of the controller memory to accommodate growth.
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Logix5000 Controller Resources
1-3
RSLinx use of Logix5000 controller memory
The amount of memory RSLinx needs depends on the type of data
RSLinx reads. The following equations provide an estimate of the
memory needed for RSLinx communications.
RSLinx overhead
(per connection)
_____ * 1345 = _____ bytes (4 connections by default)
Individual tags
_____ * 45
= _____ bytes
Arrays / structures
_____ * 7
= _____ bytes
Total = _____ bytes
Consolidating tags into an array or a structure reduces the
communications overhead and the number of connections needed to
obtain the data.
PLC/SLC memory comparison
The Logix5000 controllers used 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 will take in a Logix5000 controller by:
number PLC/SLC words ∗ 18 = number of Logix5000 bytes
Using Connections for
Communications
A Logix5000 controller uses a connection to establish a
communication link between two devices. Connections can be:
• 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 Chapter 6
“Communicating with I/O.”
• produced and consumed tags
For more information, see Chapter 4, “Sharing Tag Data with
Other Controllers.”
• messages
For more information, see Chapter 7 “Communicating with
Other Devices.”
• access to RSLogix 5000 programming software
• RSLinx software access for HMI or other software applications
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Logix5000 Controller Resources
These controllers support:
Controller:
Number of Connections:
ControlLogix
250
SoftLogix
1769-L31, -L32E, -L35E CompactLogix
100
DriveLogix
FlexLogix
1769-L20, -L30 CompactLogix
17
The limit of connections may ultimately reside in the communication
module you use for the connection. If a message path routes through
a communication module, the connection related to the message also
counts towards the connection limit of that communication module.
For this controller:
This communication device:
Supports this number of connections:
ControlLogix
1756-CNB
64 connections
depending on RPI, recommend using only 48 connections
(any combination of scheduled and message connections)
1756-ENBT
128 connections
(all connections are message connections)
CompactLogix
1769-L32E, -L35E
32 connections (over EtherNet/IP only)
FlexLogix
1788-CNx, -CNxR
32 connections
depending on RPI, as many as 22 connections can
be scheduled
PowerFlex 700S with DriveLogix
The remaining connections (or all 32, if you have no
scheduled connections) can be used for message
connections
SoftLogix5800
1788-ENBT
32 connections
(all 32 connections are message connections)
1784-PCICS
128 connections
127 of which can be scheduled connections
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Logix5000 Controller Resources
Determining Total
Connection Requirements
1-5
The total connections for a Logix5000 controller include both local
and remote connections. Tallying local connections is not an issue for
FlexLogix or CompactLogix controllers because both support the
maximum number of modules allowed in their systems. The
ControlLogix and SoftLogix controllers support more communication
modules than the other controllers, so you must tally local
connections to make sure you stay within the 250 connection limit.
Use this table to tally local connections.
Connection Type:
Device
Quantity:
x
Connections
per Module:
=
local I/O module (always a direct connection)
x
1
=
motion servo 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
=
RSLogix 5000 programming software access to controller
x
1
=
Total
Connections:
total
The communication module(s) you select determines how many
remote connections are available for I/O and information. Use this
table to tally remote connections:
Connection Type:
Device
Quantity:
x
Connections
per Module:
=
remote ControlNet communication module
configured as a direct (none) connection
configured as a rack-optimized connection
x
distributed I/O module over ControlNet (direct connection)
x
remote EtherNet/IP communication module
configured as a direct (none) connection
configured as a rack-optimized connection
x
distributed I/O module over EtherNet/IP (direct connection)
x
1
=
remote device over DeviceNet
(accounted for in rack-optimized connection for local
DeviceNet module)
x
0
=
other remote communication adapter
x
1
=
produced tag and first consumer
x
1
=
Total
Connections:
=
0 or
1
1
=
=
0 or
1
each additional consumer
1
consumed tag
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
=
total
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Logix5000 Controller Resources
Notes:
Publication 1756-RM094A-EN-P - May 2004
Chapter
2
Dividing Logic into Tasks, Programs,
and Routines
Introduction
The controller operating system is a preemptive multitasking system
that is IEC 61131-3 compliant. This environment provides:
tasks to configure
controller execution
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.
programs to group data
and logic
A task can have as many as 32 programs, each with its own routines
and program-scoped tags. Once a task is triggered (activated), all the
programs assigned to the task execute in the order in which they are
listed in the Controller Organizer.
Programs are useful for projects developed by multiple programmers.
During development, the code in one program that makes use of
program-scoped tags, can be duplicated in a second program and
minimize the possibility of tag names colliding.
routines to encapsulate
executable code written in a
single 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 “Developing Application Code in Routines” on page 2-12 for
information on selecting programming languages and how the
controller prescans and postscans logic.
1
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Dividing Logic into Tasks, Programs, and Routines
Deciding When to Use
Tasks, Programs, and
Routines
Use these considerations to determine when to use a task, program or
routine:
Comparison:
Task:
Program:
Routine:
Quantity available
varies by controller (4, 8, or 32)
32 programs per task
unlimited number of routines per
program
Function
determines how and when code
will be executed
organizes groups of routines that
need to share a common data area
contains executable code (relay
ladder, function block diagram,
sequential function chart, or
structured text) that controls the
machine
Use
• most code should reside in
a continuous task
• use a periodic task for
slower processes or when
time-based operation is
critical
Considerations
• put major equipment pieces
or plant cells into isolated
programs
• use programs to isolate
different programmers or
create reusable code
• isolate machine or cell
functions in a routine
• use the appropriate
language for the process
• modularize code into
subroutines that can be
called multiple times
• use an event task for
operations that require
synchronization to a specific
event
• configurable execution
order within a task
• a high number of tasks can
be difficult to debug
• data spanning multiple
programs must go into
controller-scoped area
• subroutines with multiple
calls can be difficult to
debug
• listed in the Controller
Organizer in the order of
execution
• data can be referenced from
program-scoped and
controller-scoped areas
• may need to disable output
processing on some tasks to
improve performance
• tasks can be inhibited to
prevent execution
• calling a large number of
routines impacts scan time
• listed in the Controller
Organizer as Main, Fault,
and then alphabetically
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Dividing Logic into Tasks, Programs, and Routines
Specifying Task Priorities
This Logix5000 controller:
2-3
Each task in the controller has a priority level that determines which
task executes when multiple tasks are triggered. A higher priority task
(such as 1) interrupts any lower priority task (such as 15). The
continuous task has the lowest priority and is always interrupted by a
periodic or event task.
Supports this many user tasks:
And has this many priority levels:
ControlLogix
32
15
1769-L35E CompactLogix
8
15
1769-L32E CompactLogix
6
15
1769-L20, -L30, -L31 CompactLogix
4
15
FlexLogix
8
15
PowerFlex 700A with DriveLogix
8
15
SoftLogix5800
32
3
If a periodic or event task is executing when another is triggered and
both tasks are at the same priority level, the tasks timeslice execution
time in 1 msec increments until one of the tasks completes execution
The Logix5000 controller has these types of tasks.
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Dividing Logic into Tasks, Programs, and Routines
Priority:
Highest
User Task:
Description:
na
CPU overhead - serial port and general CPU operations
na
Motion planner - executed at coarse update rate
na
Redundancy task - communications to 1757-SRM in redundant systems
na
Trend data collection - high-speed collection of trend data values
Priority 1 Event/Periodic
na
Priority 2 Event/Periodic
na
Priority 3 Event/Periodic
na
Priority 4 Event/Periodic
na
Priority 5 Event/Periodic
na
Priority 6 Event/Periodic
CompactLogix and FlexLogix controllers process I/O as a periodic task
based on the chassis RPI setting
Priority 7 Event/Periodic
na
Priority 8 Event/Periodic
na
Priority 9 Event/Periodic
na
Priority 10 Event/Periodic
na
Priority 11 Event/Periodic
na
Priority 12 Event/Periodic
DriveLogix communications to drives.
CompactLogix and FlexLogix communications and scheduled connection
maintenance
Lowest
Priority 13 Event/Periodic
na
Priority 14 Event/Periodic
na
Priority 15 Event/Periodic
na
Continuous
Message handler - based on system overhead timeslice
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Dividing Logic into Tasks, Programs, and Routines
Managing User Tasks
2-5
You can configure these user task:
If you want logic to execute:
Then use a:
Description:
all of the time
continuous task
The continuous task runs in the background. Any CPU time not allocated to
other operations or tasks is used to execute 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
(e.g., every 100 ms)
periodic task
• multiple times within the
scan of your other logic
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
immediately when an event
occurs
event task
An event task performs a function only when a specific event (trigger) occurs.
Whenever the trigger for 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 “Configuring an Event Task“on page 2-8 for the triggers for an event task.
Some Logix5000 controllers do not support all triggers.
The user tasks you create show up in the Tasks folder of the
controller. These pre-defined, system tasks do not show up 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
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Dividing Logic into Tasks, Programs, and Routines
Factors that Affect Task Execution
The motion planner interrupts all other tasks, regardless of their priority.
motion planner
See also “Optimizing an Application for
Motion Control“on page 8-1.
I/O processing
• 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, FlexLogix, DriveLogix, and SoftLogix controllers use a dedicated periodic task
to process I/O data. This I/O task:
• For CompactLogix, FlexLogix, and DriveLogix, operates at priority 6.
For SoftLogix, operates at Windows priority 16 (Idle).
• Higher-priority tasks take precedence over the I/O task and can impact 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.
• For local I/O, updates also occur at the end of each task.
system overhead
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.
See also “Selecting a System Overhead
Percentage“on page 2-10.
• 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 time slice 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 communication.
output processing
At the end of a task, the controller performs overhead operations (output processing) for the
output modules in your system. This output processing may effect the update of the I/O
modules in your system. You can turn off output processing for a specific task, which reduces
the elapsed time of that task.
If you have too many tasks, then:
too many tasks
• The continuous task may take too long to complete.
• Other tasks may experience overlaps. If a task is interrupted too frequently or too
long, it may not complete its execution before it is triggered again.
• Controller communications might be slower.
• If your application is designed for data collection, try to avoid multiple tasks.
Switching between multiple tasks limits communication bandwidth.
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Dividing Logic into Tasks, Programs, and Routines
2-7
The following 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 to 2 ms
periodic task 1
2
12 ms
2 ms
2 to 4 ms
I/O task—n/a to ControlLogix and
SoftLogix controllers
7
5 ms (fastest RPI)
1 ms
1 to 5 ms
system overhead
n/a
time slice = 20%
1 ms
1 to 6 ms
continuous task
n/a
n/a
20 ms
48 ms
Legend:
Task executes.
Task is interrupted (suspended).
motion
planner
event
task 1
periodic
task 1
I/O task
system
overhead
continuous
task
5
1
10
2
15
3
20
4
25
30
35
40
45
5
50
6
Description:
1
Initially, the controller executes the motion planner and the I/O task (if one exists).
2
After executing the continuous task for 4 ms, the controller triggers the system overhead.
3
The period for periodic task 1 expires (12 ms), so the task interrupts the continuous task.
4
After executing the continuous task again for 4 ms, the controller triggers the system overhead.
5
The triggers occur for event task 1.
Event task 1 waits until the motion planner is done.
Lower priority tasks experience longer delays.
6
The continuous task automatically restarts.
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Dividing Logic into Tasks, Programs, and Routines
Configuring a
Continuous Task
The continuous task is created automatically when you open an
RSLogix 5000 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 additional CPU time to load and restore task information. See
“Selecting a System Overhead Percentage” on page 2-10.
Configuring 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 communications (such as message
instructions or RSLinx communications), use a periodic task rather
than a continuous task. This avoids the overhead associated with task
switching, which can improve performance.
Configuring an Event Task
An event task executes automatically based on a preconfigured event
occurring. You can configure whether the task updates output
modules at the end of the task. After the task executes, it does not
execute again until the configured event occurs again. Each event task
requires a specific trigger that defines when the task is to execute. You
can select from:
Use this trigger:
Description:
Module Input Data State Change
The input module (digital or analog) triggers the event task based on the change of state
(COS) 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 may occur.
The ControlLogix sequence of events modules (1756-IB16ISOE, 1756-IH16ISOE) use the
Enable CST Capture feature instead of 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 new data.
Axis Registration 1 or 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 planner interrupts all other tasks, it
executes first.
EVENT instruction
Multiple EVENT instructions can trigger the same task.
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Dividing Logic into Tasks, Programs, and Routines
2-9
For more information on event tasks, see:
• Logix5000 Controllers Common Procedures Programming
Manual, publication 1756-PM001
• Using Event Tasks with Logix5000 Controllers, LOGIX-WP003
Guidelines for Configuring an Event Task
Place the I/O module being used
to trigger an event in the same
chassis as the controller
Limit events on digital inputs to
a single input bit on a module
Set the priority of the event task
as the highest priority on the
controller
Limit the number of event tasks
Placing the I/O module in a remote chassis adds additional network communications and
processing to the response time.
All inputs on a module trigger a single event, so using multiple bits increases the chance of a
task overlap. Configure 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 will have to wait
for the periodic task to complete execution.
Increasing the number of event tasks reduces the available CPU bandwidth and increases
the chances of task overlap.
Additional considerations for event tasks
Consideration:
Description:
amount of code in the event task
Each logic element (rung, instruction, structured text construct, etc…) adds to scan time.
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
executing task. (The task with the CPS or UID.)
communication interrupts
The following actions interrupt a task, regardless of the priority of the task:
• arrival of scheduled module and consumed tag information via the backplane
• serial port communication
motion planner
The motion planner takes precedence over an event task.
trends
Trend data collection takes precedence over an event task.
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Dividing Logic into Tasks, Programs, and Routines
Selecting a System
Overhead Percentage
The system overhead timeslice specifies the percentage of continuous
task execution time that is devoted to communication and background
functions. System overhead functions include:
• communicating with programming and HMI devices (such as
RSLogix 5000 software)
• responding to messages
• sending messages
• serial port message and instruction processing
The controller performs system overhead functions for up to 1 ms at a
time. If the controller completes the overhead functions in less than
1 ms, it resumes the continuous task. The following chart compares a
continuous and periodic task.
Continuous task restarts
Continuous task
10% CPU Overhead
Continuous task
25% CPU overhead
Periodic task
CPU Overhead
Periodic task restarts
Example:
Description:
Continuous task
10% CPU overhead
In the top example, the system overhead timeslice is set to 10%. Given 40 msec of code to
execute, the continuous task completes the execution in 44 msec. During a 60 msec
timespan, the controller is able to spend 5 msec on communications processing.
Continuous task
25% CPU overhead
By increasing the system overhead timeslice to 25%, the controller completes the
continuous task scan in 57 msec and spends 15 msec of a 60 msec timespan on
communications processing.
Periodic task
Placing the same code in a periodic task yields even more time for communications
processing. The bottom example assumes the code is in a 60 msec periodic task. The code
executes to completion and the goes dormant until the 60 msec, time-based trigger occurs.
While the task is dormant, all CPU bandwidth can focus on communications. Since the code
only takes 40 msec to execute, the controller can spend 20 msec on communications
processing. Depending on the amount of communications to process during this 20 msec
window, it can be delayed as it waits for other modules in the system to process all the
data that was communicated.
The Logix5000 CPU timeslices between the continuous task and
system overhead. Each task switch between user task and system
overhead takes additional CPU time to load and restore task
information. You can calculate the continuous task interval as:
ContinuousTime=(100/SystemOverheadTimeSlice%) - 1
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Dividing Logic into Tasks, Programs, and Routines
Increasing the system overhead timeslice percentage decreases execution time for the
continuous task while it increases communications performance.
Increasing the system overhead timeslice percentage also increases the amount of time it
takes to execute a continuous task - increasing overall scan time.
Tags Per
Second
Program Scan
Time
Tags per Second
impact on communications and
scan time
As the system overhead timeslice percentage increases, time allocated
to executing the continuous task decreases. If there are no
communications for the controller to manage, the controller uses the
communications time to execute the continuous task.
Program Scan Time in Milliseconds
Managing the System
Overhead Timeslice
Percentage
2-11
System Timeslice %
Individual applications may differ, but the overall impact on
communications and scan time remains the same. The above data is
based on a ControlLogix5555 controller running a continuous task
with 5000 tags (no arrays or user-defined structures).
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Dividing Logic into Tasks, Programs, and Routines
Developing Application
Code in Routines
Each routine contains logic in one programming language. Choose a
programming language based on the application
In general, if a section of your code represents:
Then use this language:
continuous or parallel execution of multiple operations (not sequenced)
ladder logic
boolean or bit-based operations
complex logical operations
message and communication processing
machine interlocking
operations that service or maintenance personnel may have to interpret in order
to troubleshoot the machine or process.
servo motion control
continuous process and drive control
function block diagram
loop control
calculations in circuit flow
high-level management of multiple operations
sequential function chart (SFC)
repetitive sequences of operations
batch process
motion control sequencing (via sequential function chart with embedded
structure text)
state machine operations
complex mathematical operations
specialized array or table loop processing
ASCII string handling or protocol processing
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structured text
Dividing Logic into Tasks, Programs, and Routines
Programming Methods
2-13
The capabilities of the Logix5000 controllers make different
programming methods possible. There are tradeoffs to consider when
selecting a programming method:
Write multiple copies of the code with different tag references.
Inline duplication
• uses more memory
• fastest execution time because
all tag references are defined
before run time
• easiest to maintain because rung
animation matches tag values
• requires more time to create and
modify
Indexed routine
• one copy of code is faster to
develop
Write one copy of code and use indexed references to data stored in
arrays.
• slowest execution time because
all tag references are calculated
at run time
• can be difficult to maintain
because the data monitor is not
synchronized to execution
The JSR instruction
passes the index
Buffered routine
• one copy operation can occur
faster than multiple index offsets
Each indexed reference
adds to scan time
Copy the values of an array into tags and reference these buffer tags
directly.
• eliminates the need to calculate
array offsets at run time
• the amount of code increases,
but so do the benefits
A user-defined structure
consolidates control data
• can be difficult to maintain
because the data monitor is not
synchronized to execution
Direct reference to a
local copy of data
The JSR instruction
passes all control
instance data
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Dividing Logic into Tasks, Programs, and Routines
Controller Prescan of Logic
On power-up, the controller prescans logic to initialize instructions.
The controller resets all state-based instructions, such as outputs
(OTE) and timers (TON). Some instructions also perform operations
during prescan. For example, the ONSR instructions turns off the
storage bit. For information on prescan, see:
• Logix5000 Controllers General Instructions Reference Manual,
publication 1756-RM003
• Logix5000 Controllers Common Procedures Programming
Manual, publication 1756-PM001
• Logix5000 Controllers Process Control and Drives Instructions
Reference Manual, publication 1756-RM006
During prescan, input values are not current and outputs are not
written.
The controller resets non-retentive I/O and internal values.
affects of prescan on relay
ladder logic
affects of prescan on function
block diagram logic
In addition to resetting non-retentive I/O and internal values, the controller clears the
EnableIn parameter for every function block diagram.
The controller resets bit tags and forces numeric tags to zero (0).
affects of prescan on structured
text logic
Use the bracketed assignment operator ([:=]) to force a value to be reset during prescan.
If you want a tag left in its last state, use the non-bracketed assignment operator (:=).
Embedded structured text follows the same rules as listed above.
affects of prescan on sequential
function chart logic
affects of prescan on array
indexed values
Controller Postscan of
SFC Logic
Publication 1756-RM094A-EN-P - May 2004
Array index values can fault the controller during prescan. If an array index value is larger
than the dimension of the array, the controller will detect a major fault during prescan. To
avoid this, make sure the index is always set properly or use a fault routine to handle this
error during prescan. See “Prescan of an Array Index” on page 3-6.
SFCs support an automatic reset option that performs a postscan of
the actions associated with a step once a transition indicates that the
step is completed. Also, every Jump to Subroutine (JSR) instruction
causes the controller to postscan the called routine. During this
postscan:
• output energize (OTE) instructions are turned off and
non-retentive timers are reset.
• in structured text code, use the bracketed assignment operator
([:=]) to have tags reset
• in structured text code, use the non-bracketed assignment
operator (:=) to have tags left in their last state.
Chapter
3
Addressing Data
Introduction
atomic data type
(BOOL, SINT, INT, DINT, REAL)
Logix5000 controllers support IEC 61131-3 atomic data types, such as
BOOL, SINT, INT, DINT, and REAL. The controllers also support
compound data types, such as arrays, predefined structures (such as
counters and timers) and user-defined structures.
Benefits:
• individual names
• each tag uses 32 bits of memory
• no limit to the number of tags
• require more communications
overhead and, potentially, more
controller memory than compound
data types
• Tag Editor and Data Monitor can
filter individual tags and display any
references
• always listed alphabetically in the
Tag Editor and Data Monitor
• full alias tag support (both the base
tag and its bits)
• can be added when programming
online
compound data type
(array, structure)
Benefits:
• can only change a tag’s data type
when programming offline
• the root tag is listed alphabetically
in the Tag Editor and Data Monitor,
but the structure members are listed
in the order in which they were
defined in the structure
Considerations:
• allow for specific names and
user-defined organization
• 2 Mbyte data limit per user-defined
structure or array
• consolidates information in
controller memory
• user-defined structures are padded
to enforce 32-bit data alignment
• optimizes communications time and
memory impact
• alias tags cannot point to the root
tag of an array
• arrays can be dynamically indexed
• Tag Editor and Data Monitor filtering
limited
• can create new arrays when
programming online
• alias support for user-defined
structures, members of an array, and
bits of a member
1
Considerations:
• can only create or change a
user-defined structure when
programming offline
• can only change an array when
programming offline
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Addressing Data
The Logix CPU reads and manipulates 32-bit data values. All data
starts at 32-bit offsets, so the minimum memory allocation for a tag is
4 bytes. When you create a standalone tag that stores data that is less
than 4 bytes, the controller allocates 4 bytes, but the data only fills the
part it needs.
Data type
Bits
31
16 15
BOOL
not used
SINT
not used
INT
not used
DINT
-2,147,483,648 to +2,147,483,647
REAL
-3.40282347E38 to -1.17549435E-38 (negative values)
8 7
1
0
0 or 1
-128 to +127
-32,768 to +32767
0
1.17549435E-38 to 3.40282347E38 (positive values)
To manipulate SINT or INT data, the controller converts the values to
DINT values, performs the programmed manipulation, and then
returns the result to a SINT or INT value. This requires additional
memory and execution time when compared to using DINT values for
the same operation.
Guidelines for Data Types
Use DINT data types whenever
possible
The Logix5000 controllers perform DINT (32 bit) and REAL (32 bit) math operations. DINT
data types use less memory and execute faster than other data types. Use:
• DINT for most numeric values and array indexes
• REAL for manipulating floating-point, analog values
• SINT (8 bit) and INT (16 bit) primarily in user-defined structures or when
communicating with an external device that does not support DINT values
SINT
INT
DINT
REAL
memory reserved for a stand-alone tag
4 bytes
4 bytes
4 bytes
4 bytes
memory reserved for data in a user-defined structure
1 byte
(8-bit aligned)
2 bytes
(16-bit aligned)
4 bytes
(32-bit aligned)
4 bytes
(32-bit aligned)
memory used to access a tag in an ADD instruction
236 bytes
260 bytes
28 bytes
44 bytes
execution time on a 1756-L63 controller required to
perform an ADD instruction
3.31 µsec
3.49 µsec
0.26 µsec
1.45 µsec
Group BOOL values into arrays
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When using BOOL values, group them into DINT arrays to best use controller memory and to
make the bits accessible via FBC or DDT instructions.
Addressing Data
Arrays
3-3
An array allocates a contiguous block of memory to store a specific
data type as a table of values.
• Tags support arrays in one, two, or three dimensions.
• User-defined structures can contain a single-dimension array as
a member of the structure.
This array:
Stores data like:
For example:
one dimension
Tag name:
Type
Dimension 0
Dimension 1
Dimension 2
one_d_array
DINT[7]
7
--
--
total number of elements = 7
valid subscript range DINT[x] where x=0–6
two dimension
Tag name:
Type
Dimension 0
Dimension 1
Dimension 2
two_d_array
DINT[4,5]
4
5
--
total number of elements = 4 ∗ 5 = 20
valid subscript range DINT[x,y] where x=0–3; y=0–4
three dimension
Tag name:
Type
Dimension 0
three_d_array
DINT[2,3,4] 2
Dimension 1
Dimension 2
3
4
total number of elements = 2 ∗ 3 ∗ 4 = 24
valid subscript range DINT[x,y,z] where x=0–1; y=0–2, z=0–3
The data type you select for an array determines how the contiguous
block of memory gets used.
BOOL[96] = 12 bytes
BOOL arrays use 32-bit
increments of memory
SINT[10] = 12 bytes of memory (2 bytes unused)
SINT arrays are padded to
use any left over bytes
INT[5] = 12 bytes of memory (2 bytes unused)
INT arrays are padded to
use any left over bytes
DINT[3] = 12 bytes and REAL[3] = 12 bytes
DINT and REAL arrays use
4-byte increments of
memory
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Addressing Data
Guidelines for Arrays
You can create arrays of most
data types, except for AXIS,
MOTION_GROUP, and
MESSAGE data types
A subscript identifies an individual element within the array. A subscript starts at 0 and
extends to the number of elements minus 1 (zero based).
• Single-dimension arrays take less memory and execute faster than 2-dimension or
3-dimension arrays.
• Direct references to array elements execute faster than indexed references
• An array can be as large as 2 Mbytes
• If you create an array of structures, the memory for each element is allocated based
on the structure definition
Type of Array
Single (1) dimension
Benefits:
Considerations:
• better support by native file instructions
• fully supported in user-defined structures and
arrays
• smallest impact (execution time and memory)
for indexed references
Double (2) dimension
and
Triple (3) dimension
• multiple arrays cannot be indirectly
referenced like in PLC or SLC processors (i.e.,
N[N7:0]:5)
• BOOL arrays not directly supported by file
instructions
• can create new arrays when programming
online
• can only be changed when programming
offline
• can provide a more accurate data
representation for a physical system
• larger impact (execution time and memory)
for indexed references
• can emulate PLC file/word indirection with a
2 dimension array
• file manipulation requires extra code in
addition to file instructions
• can create new arrays when programming
online
• can only be changed when programming
offline
Nest arrays
Select the data type of the array
based on the data, as well as
the instructions that manipulate
that data
Limit arrays to 2 Mbytes of data
Publication 1756-RM094A-EN-P - May 2004
The file instructions offer limited support for arrays. To work with array data, create a
user-defined structure with one array as a member of the structure. Then create an array tag
using the user-defined structure as its data type.
While SINT and INT arrays can compact more values into a given memory area, they require
additional memory and execution time for each instruction that references the array.
The maximum array size is 2 Mbytes. The software displays a warning if you try to create an
array that is too large. The software also displays a warning if an array is 1.5-2 Mbytes in
size, even though these sizes are valid.
Addressing Data
Indirect Addressing
of Arrays
3-5
If you want an instruction to access different elements in an array, use
a tag in the subscript of the array (an indirect address). By changing
the value of the tag, you change the element of the array that your
logic references.
When index equals 1, array[index] points here.
array[0]
4500
array[1]
6000
array[2]
3000
array[3]
2500
When index equals 2, array[index] points here.
Directly referencing an element in an array (such as MyArray[20]), uses
less memory and executes faster than an indirect reference
(MyArray[MyIndex]). You can also indirectly address bits in a tag
(MyDint.[Index]).
If you use indirect addresses, use DINT tags because other data types
require conversion and execute slower. For each indexed access to
data, the controller recalculates the array index. If you access a
specific array element multiple times, copy the data out of the array
into a fixed tag and use that tag in subsequent logic.
You can also use an expression to specify the index value. For
example: MyArray[10 + MyIndex].
• An expression uses operators to calculate a value.
• The controller computes the result of the expression and uses it
as the index.
• Valid operators include:
Optimal:
Operator:
Description:
add
DINT, REAL
LN
natural log
REAL
subtract/negate
DINT, REAL
LOG
log base 10
REAL
*
multiply
DINT, REAL
MOD
modulo-divide
DINT, REAL
/
divide
DINT, REAL
NOT
bitwise complement
DINT
Operator:
Description:
+
-
Optimal:
**
exponent (x to y)
DINT, REAL
OR
bitwise OR
DINT
ABS
absolute value
DINT, REAL
RAD
degrees to radians
DINT, REAL
ACS
arc cosine
REAL
SIN
sine
REAL
AND
bitwise AND
DINT
SQR
square root
DINT, REAL
ASN
arc sine
REAL
TAN
tangent
REAL
ATN
arc tangent
REAL
TOD
integer to BCD
DINT
COS
cosine
REAL
TRN
truncate
DINT, REAL
DEG
radians to degrees
DINT, REAL
XOR
bitwise exclusive OR
DINT
FRD
BCD to integer
DINT
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Addressing Data
Guidelines for Array Indexes
Use the SIZE instruction to
determine the number of
elements in an array
Use immediate values to
reference array elements
By determining the number of elements in an array at run time, you can write reusable code
that adjusts itself to meet each instance where it is used.
Immediate value references to array elements are quicker to process and execute faster than
indexed references.
Use DINT tags for array indexes
DINT tags execute the fastest. SINT, INT, and REAL tags require conversion code that can
add additional scan time to an operation.
Avoid using array elements as
indexes
The Logix5000 controller does not directly support the use of an array element as the index
to look up a value in another array. To work around this, you can create an alias to the
element and then use this as the index. Or copy the element to a base tag and use that base
tag as the index.
Prescan of an Array Index
During prescan, the controller resets state based on instructions such
as outputs and timers. If you use calculated array indexes based on
program execution, an “Indexed address out of range” error occurs
because the program has not executed and the index was not
initialized. You can use a fault handler routine to address this:
• Place an unconditional rung with an OTE instruction referencing
an internal bit in the first program of the first task. During
prescan, the prescan bit will be turned off. During normal scan,
the prescan bit will be on at all times.
• “Indexed address out of range” error occurs and the prescan bit
is off, reset the error and continue.
See the Logix5000 Controllers Common Procedures Programming
Manual, publication 1756-PM001 for information and sample code to
handle faults.
IMPORTANT
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This prescan condition no longer exists in controllers
with firmware revision 13 and greater. You do not
need to program a fault handler routine to handle
indexed address out-of-range errors.
Addressing Data
Guidelines for User-Defined
Structures
Group members of the same
data type within a structure
3-7
User-defined structures let you combine multiple data types into one
structure. All the elements in a structure align along 8-bit boundaries.
When you use the BOOL, SINT, or INT data types, place members that use the same data
type in sequence:
A Logix5000 controller aligns every data type along an 8-bit boundary for SINTs, a 16-bit
boundary for INTS, or a 32-bit boundary for DINTs and REALs. BOOLs also align on 8-bit
boundaries, but if they are placed adjacent to each other in a user-defined structure, they are
mapped so that they share the same byte.
Arrays within structures can
only be 1-dimension
I/O data used in structure must
be copied into the members
Limit user-defined structures to
500 members
Limit the size of user-defined
structures if they are to be
communicated
If you include an array as a member, limit the array to a single dimension. Multi-dimension
arrays are not permitted in a user-defined structure.
If you include members that represent I/O devices, you must use logic to copy the data into
the members of the structure from the corresponding I/O tags.
Logix5000 controllers limit user-defined structures to 500 members. If you need more,
consider nesting structures within the main structure.
Produced and consumed tags are limited to 500 bytes over the backplane and 480 bytes if
over a network.
RSLinx can optimize user-defined structures that are less than 480 bytes.
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Addressing Data
Selecting a Data Type for
Bit Tags
Bits in a Logix5000 controller can exist as: BOOL tags, bits in a BOOL
array, bits in elements of a SINT, INT, DINT array, members of a
user-defined structure, or as bits in a SINT, INT, DINT member of a
user-defined structure.
Each tag accesses a specific bit. Each tag uses 4 bytes.
BOOL tag
MyBit:BOOL
Benefits:
Considerations:
• each bit has a specific tag
• requires extra bandwidth to
communication
• uses more memory; 32-bits for
each tag
• cannot use FBC/DDT bit file
instructions
A BOOL array combines multiple bits into adjacent words (32-bit words).
BOOL array
BitTable:BOOL[32]
Benefits:
Considerations:
• consolidates multiple bits into a
single word
• BOOL data type only supported by
bit instructions
• better use of memory
• cannot use file instructions, copy
instructions, or DDT/FBC
instructions
• can address all bits in an array using
indirect addressing
A DINT combines multiple bits into adjacent words.
DINT array
FaultTable:DINT[3]
Benefits:
Considerations:
• consolidates multiple bits into a
single word
• requires extra planning to indirectly
address bits
• file instructions, copy instructions,
and DDT/FBC instructions support
DINT arrays
• difficult to address bits in the array
using indirect addressing
• lets you access the bits by element
(word) and bit number
A user-defined structure combines multiple bits into adjacent, individually-named words.
user-defined structure
BitStructure
Bit1:BOOL
Bit2:BOOL
Fault:BitStructure
Benefits:
• object based
• consolidates multiple bits into a
single word
Considerations:
• structures are not directly supported
by 3rd party MMI/EOI products
(RSView does support 32-bit tags
and structures)
• cannot use FBC/DDT bit file
instructions
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Addressing Data
Serial Bit Addressing
3-9
The BOOL “B” data table in the PLC-5 and SLC 500 processors
supports two addressing modes that can address the same bit:
Addressing mode:
Description:
serial bit
Serial bit addressing provides the ability to reference all bits as a contiguous list (array) of
bits. For example, if you wanted to reference the 3rd bit in the 2nd word of a “B” file, you
specify B3/18. This method similar to a BOOL array in a Logix5000 controller where you
would specify FaultBit[18].
In PLC-5 or SLC software, this addressing
mode is represented as “/Bit”
word bit
In PLC-5 or SLC software, this addressing
mode is represented as “Word/Bit”
Word bit addressing identifies a bit within a specific word. For example, B3:1/2 is the
same as B3/18 from the serial bit example. This method is similar to accessing the bits of
a SINT, INT, DINT array in a Logix5000 controller where you would specify FaultTable[1].2.
The Logix5000 controller supports both of these addressing modes,
but you cannot use both to reference bits in the same array due to
conformance with the IEC 61131-3 standard. Choose the method that
best meets your application needs. You can copy data between arrays
using both methods.
You can also use an expression to indirectly reference a bit in a DINT
array using a serialized bit number. For example:
Tag
MyBits : DINT[10]
BitRef : DINT
EndTag
MOV(34, BitRef)
XIC(MyBits[BitRef / 32].[BitRef AND 31])
where:
This expression:
Calculates the:
[BitRef / 32]
element in the DINT array
Note: If the tag MyBits is an INT or SINT, the divisor would be 16 or 8, respectively.
[BitRef AND 31]
bit within the element
Note: If the tag MyBits is an INT or SINT, the mask value would be 15 or 7, respectively.
The Diagnostic Detect (DDT) and File Bit Compare (FBC) instructions
provide a bit number as a result of their operation. These instructions
are limited to DINT arrays so you can use them to locate the bit
number returned from the example above.
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Addressing Data
Guidelines for String
Data Types
You can create a string data type
that is longer or shorter than the
default string data type
String data types are structures that hold ASCII characters. The first
member of the structure defines the length of the string; the second
member is an array that holds the actual ASCII characters.
The default string data type can contain as many as 82 characters, but you can create
custom-length string data types to hold as many characters as needed.
These comparison instructions support string tags: EQU, NEQ, GRT, GEG, LES, LEQ, CMP.
Only some instructions support
string data types
These serial port instructions support string tags: ARD, ARL, AWA, AWT.
These string-handling instructions support string tags: STOD, DTOS, STOR, RTOS, CONCAT,
MID, FIND, DELETE, INSERT, UPPER, LOWER, SIZE.
These file instructions support string arrays: FAL, FFL, FFU, LFL, LFU, COP, CPS, FSC.
Use the SIZE instruction to
determine the number of
characters in a string
Using the DTOS, RTOS, and
CONCAT instructions, you can
embed tag values within a
string
PLC-5/SLC 500 Access of
Strings
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By determining the number of characters in a string at run time, you can write reusable code
that adjusts itself to meet each instance where it is used.
The SLC 500 processor supports the ability to embed a data table reference address within a
string (inline indirection). The SLC 500 AWA and AWT instructions can then look up the data
value and place an ASCII representation into the outgoing string. The Logix5000 controller
does not directly support this ability. Use the DTOS or RTOS instructions to convert a value to
a string and the CONCAT instruction to merge characters with another string.
The ASCII “A” data table in the PLC-5 and SLC 500 processors uses a
string format that is similar to the Logix string data type. The main
difference is that the LEN field (length) in a PLC-5/SLC 500 processor
is a 16-bit, INT value whereas the LEN field in a Logix5000 controller
is a 32-bit, DINT field. This difference can impact converted logic and
data communications. The Logix5000 controller will convert the LEN
field to the appropriate value and size when a PLC-5/SLC 500 message
format is used to read or write a string.
Addressing Data
Configuring Tags
3-11
A tag is a text-based name for an area of the controller’s memory
where data is stored. Tags are the basic mechanism for allocating
memory, referencing data from logic, and monitoring data.
If you want the tag to:
Then choose this type:
store a value for use by logic within the project
Base
use a different name for an existing tag’s data
Alias
(can help simplify long, pre-determined tag names,
such as for I/O data or user-defined structures)
send (broadcast) data to another controller
Produced
receive data from another controller
Consumed
For more information on I/O tags, see Chapter 6 “Communicating
with I/O.”
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Addressing Data
Guidelines for Base Tags
The controller supports pre-defined, stand-alone tags.
Create stand-alone atomic tags
• Atomic tags are listed directly in the Tag Editor and Data Monitor and can be easily
located by browsing the alphabetical list.
• Atomic tags can be created on-line, but the data type can only be modified off-line.
• Using only atomic tags can impact HMI communications performance as more
information must be passed and acted on.
Create user-defined structures
User-defined structures (data types) let you organize your data to match your machine or
process.
• One tag contains all the data related to a specific aspect of your system. This keeps
related data together and easy to locate, regardless of its data type.
• Each piece of data (member) gets a descriptive name.
• You can use the structure to create multiple tags with the same data layout.
• User-defined structure can only be modified off-line
• RSLinx optimizes user-defined structures more than stand-alone tags.
An array creates multiple instances of a data type under a common tag name.
Use arrays like files to quickly
create a group of similar tags
• Arrays let you organize a block of tags that use the same data type and perform a
similar function.
• You organize the data in 1, 2, or 3 dimensions to match what the data represents.
• Arrays can only be modified off-line.
• RSLinx optimizes array data types more than stand-alone tags.
Minimize the use of BOOL arrays. Many array instructions do not operate on BOOL arrays.
This makes it more difficult to initialize and clear an array of BOOL data.
Take advantage of
program-scoped tags
If you want multiple tags with the same name, define each tag at the program scope
(program tags) for a different program. This lets you re-use both logic and tag names in
multiple programs.
Avoid using the same name for both a controller tag and a program tag. Within a program,
you cannot reference a controller tag if a tag of the same name exists as a program tag for
that program.
Use mixed case and the
underscore characters
Although tags are not case sensitive (upper case A is the same as lower case a), mixed case
is easier to read. For example, “Tank_1” can be easier to read than “tank1.”
Consider alphabetical order
RSLogix 5000 software displays tags of the same scope in alphabetical order. To make it
easier to monitor related tags, use similar starting characters for tags that you want to keep
together. For example, consider using “Tank_North” and “Tank_South” rather than
North_Tank” and “South_Tank.”
Use leading zeroes (0) when
numbers are part of tag names
RSLogix 5000 software uses a simple sort to alphabetize tag names in the Tag Editor and
Data Monitor. This means if you have Tag1, Tag2, Tag11, and Tag12, the software displays
them in order as Tag1, Tag11, Tag12, and then Tag2. If you want to keep them in numerical
order, name them Tag01, Tag02, Tag11, and Tag12.
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Addressing Data
Creating Alias Tags
3-13
An alias tag lets you create one tag that represents another tag.
• both tags share the same value as defined by the base tag
• when the value of a base tag changes, all references (aliases) to
the base tag reflect the change
When assigning aliases, avoid
An alias tag references a
base tag
• nesting aliases (you cannot have an alias of an alias)
• using multiple aliases to the same tag
On upload, the software decompiles the program and uses the physical memory addresses to
determine which tags are referenced in the code. All references to a base tag reverts to an
alias if one exists. If multiple aliases point to the same tag, RSLogix 5000 software uses the
first alias tag (alphabetically) that it finds.
Alias tags do not affect
controller execution
During download, the program is compiled into machine executable code and physical
memory addresses. While the existence of an alias requires controller memory to store the
name, the program performs the same operation for a reference with an alias or its
associated base tag.
Accessing alias tags from
RSLinx software
Because an alias tag appears as a stand-alone tag to RSLinx software, an alias tag that
references a compound array or structure might require additional communication time.
When referencing tags from RSLinx software or other HMI, it might be fastest to reference
base tags directly.
Guidelines for Data Scope
controller
scope
program
scope
Data scope defines where you can access tags. When you create a tag,
you assign scope as either controller or program. Controller-scoped
tags are accessible by all programs. Program-scoped tags are only
accessible by the code within a specific program.
If you want to:
Then assign this scope:
use a tag in more than one program in the
same project
controller scope (controller tags)
use a tag in a message (MSG) instruction
produce or consume data
use motion tags
communicate with a PanelView terminal
reuse the same tag name multiple times for
different parts or processes within a controller
program scope (program tags)
have multiple programmers working on logic
and you want to merge logic into one project
Isolate portions of a machine or different stations into separate
programs and use program-scoped tags within each program. This:
• provides isolation between programs
• prevents tag name collisions
• improves the ability to reuse code
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Addressing Data
Notes:
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Chapter
4
Sharing Tag Data with Other Controllers
(Produced and Consumed Tags)
Introduction
Logix5000 controllers support the ability to produce (broadcast) and
consume (receive) system-shared tags.
For two controllers to share produced or consumed tags, both
controllers must be attached to the same control network (such as a
ControlNet or Ethernet/IP network). You cannot bridge produced and
consumed tags over two networks.
Logix5000 controllers can produce and consume tags over these
networks (as long as they support communications over these
networks):
• the ControlLogix backplane
• a ControlNet network
• an EtherNet/IP network
If there are no other connections, the controller supports:
As a:
The controller supports:
producer
(number of produced tags) ≤ 127
consumer
(number of consumed tags) ≤ 250 (or controller maximum)
The total combined number of consumed and produced tags that a
controller supports is:
(produced tags) + (consumed tags) + (other connections) ≤ 250 (or controller maximum)
IMPORTANT
1
The actual number of produced and consumed tags
that you can configure in project depends on the
connection limits of the communication module
through which you produce or consume the tags.
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Sharing Tag Data with Other Controllers (Produced and Consumed Tags)
Guidelines for Creating Produced and Consumed Tags
You cannot bridge produced and
consumed tags over different
networks
For two controllers to share produced or consumed tags, both controllers must be attached
to the same network. You can produce and consume tags over ControlNet or EtherNet/IP
networks.
You can only produce and consume (share) controller-scoped tags.
Create the tag at controller
scope
If you transfer a tag with more than 500 bytes, create logic to transfer the data in packets.
Limit the size of the tag
to ≤ 500 bytes
If you consume a tag over a ControlNet hop, the tag must be ≤ 480 bytes. This is a limitation
of the ControlNet network, not the controller.
If you are producing several tags for the same controller:
Combine data that goes to the
same controller
• Group the data into one or more user-defined structures. This uses less connections
than producing each tag separately.
• Group the data according to similar update intervals. To conserve network
bandwidth, use a greater RPI for less critical data.
Use one of these data types:
• DINT
To share data types other than DINT or REAL, create a user-defined structure to contain the
required data.
Use the same data type for the produced tag and the corresponding consumed tag or tags.
• REAL
• array of DINTs or REALs
• user-defined structure
Use a user-defined structure to
produce or consume INT or
SINT data
The data type in the producer
and the consumer must match
Produce tags based on
user-defined structures to
non-Logix devices
Use a CPS instruction to buffer
produced and consumed data
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To produce or consume INT or SINT data, create a user-defined structure with INT or SINT
members. The members can be individual INTs or SINTs or the members can be INT or SINT
arrays. The resulting user-defined structure can then be produced or consumed.
The data type for a produced or consumed tag must be the same in both the producer and
the consumer.
The controller produces tags in 32-bit words. For devices that communicate in other word
boundaries, such as 16-bit words, the resulting data in the target device can be misaligned.
To help avoid misalignment, structure the produced data in a user-defined structure.
Use the CPS instruction to copy the data to the outgoing tag on the producer side. Then use
another CPS instruction to copy the data into a buffer tag on the consumer side.
The CPS instructions provides data integrity for data structures greater than 32 bits.
Sharing Tag Data with Other Controllers (Produced and Consumed Tags)
Guidelines for Specifying
an RPI Rate
Make sure the RPI is equal to or
greater than the NUT
The smallest (fastest) consumer
RPI determines the RPI for the
produced tag
4-3
When configuring produced and consumed tags, you specify an
Requested Packet Interval (RPI) rate. The RPI value is the rate at
which the controller attempts to communicate with the module.
You use RSNetWorx for ControlNet software to select the network update time (NUT) and
the software schedules the network connections.
RSNetWorx cannot schedule a ControlNet network if a module and/or produced/consumed
tag on the network has an RPI that is faster than the network update time.
If multiple consumers request the same tag, the smallest (fastest) request determines the
rate at which the tag is produced for all the consumers.
Guidelines for Managing Connections for Produced and Consumed Tags
Minimize the use of produced
and consumed tags
To reduce network traffic, minimize the size of produced and consumed tags. Also, minimize
the use of produced and consumed tags to high-speed, deterministic data, such
as interlocks.
Use arrays or user-defined
structures
When sending multiple tags to the same controller, use an array or user-defined structure to
consolidate the data. The byte limit of ≤ 500 bytes per produced and consumed tag
still applies.
Configure the number of
consumers accurately
Make sure the number of consumers configured for a produced tag is the actual number of
controllers that will consume the tag. If you set the number higher than the actual number of
controllers, you unnecessarily use up connections.
The default is 2 consumers per produced tag.
Multiple produced/consumed
connections are linked
Configuring an Event Task
Based on a Consumed Tag
If there are multiple produced and consumed connections between two controllers and one
connection fails, all the produced and consumed connections fail.
Consider combining all produced and consumed data into one structure or array so that you
only need one connection between the controllers.
An event task executes automatically based on a preconfigured event
occurring. One such event can be the arrival of a consumed tag.
• Only one consumed tag can trigger a specific event task.
• Typically, use an IOT instruction in the producing controller to
signal the production of new data.
• When a consumed tag triggers an event task, the event task
waits for all the data to arrive before the event task executes.
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Sharing Tag Data with Other Controllers (Produced and Consumed Tags)
For information on configuring an event task, see Chapter 2 “Dividing
Logic into Tasks, Programs, and Routines.”
Comparing Messages and Produced/Consumed Tags
Method:
Read/Write Message
Benefits:
• programatically initiated
• communications and network resources only
used when needed
• support automatic fragmentation and
reassembly of large data packets, up to as
many as 32,767 elements
• some connections can be cached to improve
re-transmission time
• Generic CIP message useful for third-party
devices
Produced/Consumed Tag
• configured once and sent automatically
based on Requested Packet Interval (RPI)
• multiple consumers can simultaneously
receive the same data from a single
produced tag
• can trigger an event task when consumed
data arrives
• ControlNet resources are reserved up front
• does not impact the scan of the controller
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Considerations:
• controller limited to 32 active messages
active at the same time (limit of 16 in
revision 11 and earlier)
• delay may occur if resources are not
available when needed
• MSG instruction and processing impacts
controller scan (system overhead timeslice)
• data arrives asynchronous to program scan
(use CPS instruction to reduce impact, no
event task support)
• fragmentation and reassembly limited to
exchanges between Logix5000 controllers
• support limited to Logix5000 and PLC-5
controllers, and the 1784-KTCS I/O Linx and
select third party devices
• limited to 500 bytes over the backplane and
480 bytes over a network
• must be scheduled when using ControlNet
• data arrives asynchronous to program scan
(use CPS instruction and event tasks to
synchronize)
• connection status must be obtained
separately
Chapter
5
Designing Networks
Introduction
NetLinx Open Network Architecture is the Rockwell Automation
strategy of using open networking technology for seamless, top-floor
to shop-floor integration. The networks in the NetLinx architecture —
DeviceNet, ControlNet, and EtherNet/IP — share a universal set of
communication services. These are the recommended networks for
Logix control systems.
Select a Network
Comparison:
ControlNet:
DeviceNet:
Control I/O
better
BEST
low density
Configuration devices
BEST
BEST
BEST
Collect data
BEST
Better
good
Peer interlocking
better
BEST
good
Devices
better
better
BEST
star
trunkline/dropline
trunkline/dropline
requires switches
star with repeaters
many nodes
99 nodes
63 nodes
BEST
BEST
good
Topologies
Capacity
Performance
1
EtherNet/IP:
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Designing Networks
EtherNet/IP Network Topology
EtherNet/IP network:
• EtherNet/IP supports messaging, produced/consumed tags,
and distributed I/O
• EtherNet/IP supports half/full duplex 10 Mbps or 100 Mbps
operation
Topology:
example 1
device
• EtherNet/IP requires no network scheduling and no routing
tables
• There are several methods available to configure EtherNet/IP
network parameters for devices. Not all methods are available
at all times. These methods are device and configuration
dependent.
switch
device
device
example 2
− DHCP
router
− Rockwell Automation BOOTP/DHCP utility
− RSLinx software
switch
switch
− RSLogix 5000 software
− RSNetWorx for EtherNet/IP software
Application Ideas
• connect many computers
• default gateway to business systems
• star topology best for few nodes and short distances
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device
device
device
device
Designing Networks
5-3
Guidelines for EtherNet/IP
For EtherNet/IP control, you must use an industrial-grade switch that supports:
Make sure the switch has the
required features
• full-duplex on all ports
• IGMP snooping
− constrains multicast traffic to ports associated with a specific IP multicast group
− most switches require a router for IGMP snooping to function
− if you have a stand-alone network, make sure the switch supports IGMP snooping
without a router present
• port mirroring
• VLAN (virtual local area network) to isolate traffic flow for different systems
• both autonegotiation and manual configuration of duplex and speed
• wire-speed switching fabric
• SNMP (Simple Network Management Protocol) to obtain statistical information
about a device
• IEEE 802.1D spanning tree protocol to support redundant backbone connections for
improved fault tolerances
• IEEE 802.1P frame prioritization
• IP address blocking to restrict traffic to a specific range
• auto-restore of switch configuration for replacement
• per port broadcast and multicast storm control
• port trunking for applications with multiple switches
• method for backing up configuration information
Consider using switches from
Encompass partners
These Encompass partners have switches that meet the required features: Cisco,
Hirschmann, and N-Tron.
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Designing Networks
ControlNet Network Topology
ControlNet network:
Topology:
• ControlNet allows both I/O and messaging on the same wire.
• Multiple controllers and their respective I/O can also be placed
on the same ControlNet wire.
Shared
I/O
• When new I/O is added or an existing I/O module’s
communication structure is changed, you must use RSNetWorx
for ControlNet software to reschedule the network.
ControlNet
• If the network timing changes, every device with scheduled
traffic on the network is affected.
CPU
I/O
ControlNet
• Place shared I/O and produced/consumed tags on a common
network available to each CPU that needs the information.
ControlNet
• To reduce the impact of changes, place each CPU and its
respective I/O on isolated ControlNet networks.
CPU
I/O
Application Ideas
• default Logix network
• best replacement for Universal Remote I/O
• backbone to multiple distributed DeviceNet networks
• peer interlocking network
• common devices include: Logix5000 controllers, PanelView
terminals, I/O modules, and drives
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I/O
I/O
Designing Networks
5-5
Guidelines for ControlNet
Use these publications when installing a ControlNet network:
Use the installation
publications when installing a
ControlNet network
Limit the number of nodes per
ControlNet network to 40
• ControlNet Coax Media Planning and Installation Guide, publication CNET-IN002
• ControlNet Fiber Media Planning and Installation Guide, publication CNET-IN001
ControlNet was designed with a limit of 99 nodes per network, but this number of nodes
decreases network performance. A maximum of 40 nodes per network results in better
performance and leaves bandwidth for other communications.
Change these settings in the RSNetWorx for ControlNet software:
Adjust the default RSNetWorx
settings
• UMAX (highest unscheduled node on the network)
− default is 99
− the network takes the time to process the total number of nodes specified in this
setting, even if there are not that many devices on the network
− change to a reasonable level to accommodate the active devices on the network
and any additional devices that might be connected
• SMAX (highest scheduled node on the network)
− default is 1
− this must be changed for all systems
− set SMAX < UMAX
Design for at least 400 Kbytes of
available, unscheduled network
bandwidth
Place DeviceNet (DNB) and
serial (MVI) communication
modules in the local chassis
Limit 1756-CNB, -CNBR
connections
Leaving too little memory for unscheduled network bandwidth results in poor message
throughput and slower workstation reponse.
DeviceNet (DNB) and serial (MVI) communication modules have multiple, 500-byte data
packets that will impact scheduled bandwidth. Placing these modules in the same chassis as
the controller avoids this data being scheduled over the ControlNet network
If you must place these communication devices in remote chassis, configure the input and
output sizes to match the data configured in RSNetWorx for DeviceNet software. This
reduces the amount of data that must be transmitted.
For best performance, limit the 1756-CNB, -CNBR to 40-48 connections. Add additional
modules in the same chassis if you need more connections. Adding more modules and
splitting connections among the modules can improve system performance.
If the chassis that contains the CNB module also contains multiple digital I/O modules,
configure the CNB module’s communication format for “Rack Optimization.” Otherwise, use
“None.” See the examples on page 6-5.
If you change network settings,
resave each controller’s project
Any time you use RSNetWorx software and you save or merge your edits, attach to each
controller in the system with their respective RSLogix 5000 project file and perform a save.
This copies the ControlNet settings into the offline, database file and ensures that future
downloads of the controller permit it to go online without having to run RSNetWorx
software.
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Designing Networks
DeviceNet Network Topology
DeviceNet network:
• You need a DeviceNet scanner to connect
the controller to DeviceNet devices
• You must use RSNetWorx for DeviceNet
to configure devices and create the
scanlist for the scanner.
• You can configure the network baud rate
as 125K bit/s (default and a good starting
point), 250K bit/s, or 500K bit/s.
• If each device on the network (except the
scanner) sends ≤ 4 bytes of input data
and receives ≤ 4 bytes of output data,
you can use the AutoScan feature on the
scanner to configure the network.
Application Ideas
• distributed devices
• drives network
• diagnostic information
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Topology:
single network
CPU
scanner
device
device
device
device
device
several smaller distributed networks (subnets)
linking
device
CPU
device
device
linking
device
device
device
device
device
Designing Networks
5-7
Guidelines for DeviceNet
Use this publication when installing a DeviceNet network:
Use the installation
publications when installing a
DeviceNet network
Place DeviceNet (DNB)
communication modules in the
local chassis
• DeviceNet Cable System Manual, publication DN-UM072
Placing DNB modules in the local chassis maximizes performance, especially in ControlLogix
systems.
Size the input and output image for the DNB modules to the actual devices that are
connected plus 20% for future growth. If you have to place DNB modules in remote chassis,
sizing the input and output images is critical for best performance.
A DNB supports:
Verify the total network data
does not exceed the maximum
DNB data table size
• 124, 32-bit input words
• 123 32-bit output words
• 32, 32-bit status words
You can use RSNetWorx for DeviceNet software offline to estimate network data. Use a
second DNB if there is more network data than one module can support.
Set up slaves first
Configure a device’s parameters before adding that device to the scanlist. You cannot
change the configuration of many devices once they are already in the scanlist.
If you configure the scanner first, there is a chance that the scanner configuration will not
match the current configuration for a device. If the configuration does not match, the device
will not show up when you browse the network.
Leave node address 63 open to
add nodes
Leave node address 62 open to
connect a computer
Don’t forget to set the scanner
run bit
Make sure you have the most
current EDS files for your
devices
Devices default to node 63 out-of-the-box. Leave node address 63 unused so you can add a
new devices to the network. Then change the address of the new device.
Always leave at least one open node number to let a computer be attached to the network if
needed for troubleshooting, configuration, etc.
For the scanner to be in Run mode, the controller must be in Run mode and the logic in the
controller must set the scanner’s run bit.
RSNetWorx for DeviceNet software uses EDS file to recognize devices. If the software is not
properly recognizing a device, you are missing the correct EDS file(s). For some devices, you
can create an EDS file by uploading information from the device. Or you can get EDS files
from: http://www.ab.com/networks/eds.
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Designing Networks
Notes:
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Chapter
6
Communicating with I/O
Introduction
In Logix5000 controllers, I/O values update at a period (Requested
Packet Interval, RPI) that you configure via Module Property dialog in
the I/O configuration folder of the project. The values update
asynchronously to the execution of logic.
The module sends input values to the controller at the specified RPI.
Because this transfer is asynchronous to the execution of logic, an I/O
value in the controller can change in the middle of a scan.
Buffering I/O Data
If you reference an I/O tag multiple times and the application could
be impacted if the value changes during a program scan, you must
copy the I/O value into a buffer tag prior to the first reference of that
tag in your code. In your code, reference the buffer tag rather than the
I/O tag.
Use the synchronous copy (CPS) instruction to buffer I/O data. While
the CPS instruction copies data, no I/O updates or other tasks can
change the data. Tasks that attempt to interrupt a CPS instruction are
delayed until the instruction is done. Buffer I/O data to:
• prevent an input or output value from changing during the
execution of a program. (I/O updates asynchronous to the
execution of logic.)
• copy an input or output tag to a member of a structure or
element of an array.
• prevent produced or consumed data from changing during the
execution of a program.
• ensure all produced and consumed data arrives or is sent as a
group (not mixed from multiple transfers)
• only use the CPS instruction if the I/O data that you want to
buffer is greater than 32 bits (or 4 bytes) in size
If you have a user-defined structure with members that represent I/O
devices, you must use logic to copy the data into the members of the
structure from the corresponding I/O tags
1
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6-2
Communicating with I/O
Guidelines for Specifying
an RPI Rate for I/O Modules
When adding I/O modules to a controller project, you specify a
Requested Packet Interval (RPI) rate. Depending on the controller
platform, you can select an RPI rate per module (ControlLogix) or an
RPI rate per controller (CompactLogix and FlexLogix).
The RPI value is the rate at which the controller attempts to
communicate with the module.
Specify an RPI at 50% of the rate
you actually need
Setting the RPI faster (specifying a smaller number) than what your application needs
wastes network resources, such as ControlNet schedule bandwidth, network processing
time, and CPU processing time.
For example, if you need information every 80 msec, set the RPI at 40 msec. The data is
asynchronous to the controller scan, so you sample data twice as often (but no faster) than
you need it to make sure you have the most current data.
Group devices with similar
performance needs onto the
same module
Set the ControlNet network
update time (NUT) equal to or
less than the fastest RPI
The RPI should be an even
multiple of the NUT
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By grouping devices with similar performance needs on the same module, you consolidate
data transmission to one module rather than multiple modules. This conserves network
bandwidth.
When configuring a ControlNet network, set the network update time (NUT) equal to or less
than the fastest RPI of the I/O modules and produced/consumed tags in the system. For
example, if your fastest RPI is 10 msec, set the NUT to 5 msec for more flexibility in
scheduling the network.
Set the RPI to a binary multiple of the NUT. For example, if the NUT is 10 msec, select an RPI
such as 10, 20, 40, 80, 160, etc. msec.
Communicating with I/O
Communication Formats for
I/O Modules
direct connection
6-3
The communication format determines whether the controller
connects to the I/O module via a direct or a rack-optimized
connection. The communication format also determines the type and
quantity of information that the module will provide or use.
Each module passes its data to/from the controller individually.
Communication modules bridge data across networks.
digital inputs
communication
module
Local chassis
Benefits:
digital outputs
communication
module
controller
Remote chassis
Considerations:
• each module can determine its own rate (RPI)
• requires additional connections and network resources
• more data can be sent per module, such as diagnostic and
analog data
• this is the only method supported in the local chassis
• I/O data presented as individual tags
• supports event task communications
rack-optimized connection
The communications module in a remote chassis consolidates data
from multiple modules into a single packet and transmits that packet
as a single connection to the controller.
digital inputs
communication
module
communication
module
Local chassis
digital outputs
controller
Remote chassis
.
Benefits:
Considerations:
• one connection can service a full chassis of digital modules
• all modules are sent at the same rate
• reduces network resources and loading
• unused slots are still communicated
• still need a direct connection for analog and diagnostic data
• limited to remote chassis
• I/O data presented as arrays with alias tags for each module
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6-4
Communicating with I/O
The rack-optimized format limits data to a single 32-bit input word per
module in a chassis. If you place a diagnostic module in a chassis, the
rack-optimized format eliminates the value that the diagnostic module
offers. In this case, it’s better to use a direct connection so that all of
the module's diagnostic information is passed to the controller.
Guidelines for Managing I/O Connections
The type of I/O module can
determine the type of
connection
Analog modules always use direct connections, except for 1771 analog modules which use
connected messaging.
Digital modules can use direct or rack-optimized connections. Communication formats that
include “optimization” in the title are rack-optimized connections; all other connection
options are direct connections.
For a remote adapter:
Select the communication format
for a remote adapter based on the
remote I/O modules
Use rack-optimized
connections to conserve
connection use
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Select:
If:
None
the remote chassis contains only analog modules,
diagnostic digital modules, fused output modules, or
communication modules
Rack-Optimized
the remote chassis only contains standard, digital
input and output modules (no diagnostic modules or
fused output modules)
Listen Only Rack-Optimized
you want to receive I/O module and chassis slot
information from a rack-optimized remote chassis
owned by another controller
If you are trying to limit the number of controller and network connections, rack-optimized
connections can help.
Communicating with I/O
6-5
Guidelines for Managing I/O Connections (continued)
In some cases, all direct
connections work best
For a remote adapter module configured for rack-optimized connections, there is always data
sent for each slot in the chassis, even if a slot is empty or contains a direct connection
module. There are 12 bytes of data transferred for rack-optimized overhead between the
controller and the remote adapter module. In addition, the remote adapter module sends
8 bytes per slot to the controller; the controller sends 4 bytes per slot to the remote adapter.
For a small number of digital modules in a large chassis, it might be better to use direct
connections because transferring the full chassis information might require more system
bandwidth than direct connections to a few modules.
For example:
Example:
Description:
Remote 17-slot chassis
Option 1: Select Rack Optimization for remote adapter’s communication format. This
example uses 16 controller connections (15 for analog modules and 1 for the
rack-optimized connection). This example also transfers:
Slot 0: 1756-CNBR/D
Slots 1-15: analog modules
• 12 bytes for rack-optimized overhead
Slot 16: standard digital module
• 12 bytes for the digital module
• 12 bytes for each of the 15 analog modules, for a total of 180 bytes
Option 2: Select None for the remote adapter’s communication format. This example also
uses 16 controller connections (1 direct connection to each I/O module). There is no
rack-optimized overhead data to transfer.
Recommendation: Option 2 is recommended because it avoids unnecessary network
traffic, and thus improves network performance.
Remote 17-slot chassis
Slot 0: 1756-CNBR/D
Option 1: Select Rack Optimization for the remote adapter’s communication format. This
example uses 9 controller connections (8 for analog modules and 1 for the rack-optimized
connection). This example also transfers:
Slots 1-8: analog modules
• 12 bytes for rack-optimized overhead
Slots 9-16: digital modules
• 12 bytes for each of the 8 digital modules, for a total of bytes 96 bytes
• 12 bytes for each of the 8 analog modules, for a total of 96 bytes
Option 2: Select None for remote adapter’s communication format. This example uses
16 controller connections (1 direct connection to each I/O module). There is no
rack-optimized overhead data to transfer.
Recommendation: The best option for this example depends on the type of digital I/O
modules in the system and other controller connections. If the total system has many
analog modules, diagnostic modules, fused output modules, or produced/consumed tags,
select Option 1 to conserve controller connections. If there are plenty of controller
connections available, select Option 2 to reduce unnecessary network traffic.
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6-6
Communicating with I/O
Creating Tags for I/O Data
Each I/O tag is automatically created when you configure the I/O
module through the programming software. Each tag name follows
this format:
Location:SlotNumber:Type.MemberName.SubMemberName.Bit
This address variable:
Is:
Location
Identifies network location
LOCAL = local chassis or DIN rail
ADAPTER_NAME = identifies remote adapter or bridge
SlotNumber
Slot number of I/O module in its chassis
Type
Type of data:
I = input
C = configuration
O = output
S = status
MemberName
Specific data from the I/O module, such as Data and Fault; depends on the module
SubMemberName
Specific data related to a MemberName.
Bit (optional)
Specific point on the I/O module; depends on the size of the I/O module (0-31 for a 32-point module)
If you configure a rack-optimized connection, the software creates a
rack-object tag for the remote communication module. You can
reference the rack-optimized I/O module individually, or by its
element within the rack-object tag.
For example, a remote ControlNet communication
module (remote_cnb) has an I/O module in slot 1.
This is the individual tag created for
the I/O module in remote slot 1.
This is the entry in the rack-object tag
for the remote communication module
that identifies the I/O module in
remote slot 1.
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Communicating with I/O
Controller Ownership
6-7
When you choose a communication format, you have to choose
whether to establish an owner or listen-only relationship with the
module.
The owner controller writes configuration data and can establish a connection to the
module.
owner
A controller using a listen-only connection only monitors the module. It does not write
configuration data and can only maintain a connection to the I/O module when the owner
controller is actively controlling the I/O module.
listen-only
There is a noted difference in controlling input modules versus
controlling output modules.
Controlling:
This ownership:
Description:
input modules
owner
An input module is configured by a controller that establishes a connection as an owner.
This configuring controller is the first controller to establish an owner connection.
Once an input module has been configured (and owned by a controller), other controllers
can establish owner connections to that module. This allows additional owners to
continue to receive multicast data if the original owner controller breaks its connection
to the module. All other additional owners must have the identical configuration data
and identical communications format that the original owner controller has, otherwise
the connection attempt is rejected.
output modules
listen-only
Once an input module has been configured (and owned by a controller), other controllers
can establish a listen-only connection to that module. These controllers can receive
multicast data while another controller owns the module. If all owner controllers break
their connections to the input module, all controllers with listen-only connections no
longer receive multicast data.
owner
An output module is configured by a controller that establishes a connection as an
owner. Only one owner connection is allowed for an output module. If another controller
attempts to establish an owner connection, the connection attempt is rejected.
listen-only
Once an output module has been configured (and owned by one controller), other
controllers can establish listen-only connections to that module. These controllers can
receive multicast data while another controller owns the module. If the owner controller
breaks its connection to the output module, all controllers with listen-only connections
no longer receive multicast data.
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Communicating with I/O
Notes:
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Chapter
7
Communicating with Other Devices
Introduction
The MSG instruction asynchronously reads or writes a block of data to
another device.
If the target device is a:
Select one of these message types:
Logix5000 controller
CIP Data Table Read
CIP Data Table Write
I/O module that you configure using
RSLogix 5000 software
Module Reconfigure
PLC-5 controller
PLC5 Typed Read
CIP Generic
PLC5 Typed Write
PLC5 Word Range Read
PLC5 Word Range Write
SLC controller
SLC Typed Read
MicroLogix controller
SLC Typed Write
Block-transfer module
Block-Transfer Read
Block-Transfer Write
PLC-3 processor
PLC3 typed read
PLC3 typed write
PLC3 word range read
PLC3 word range write
PLC-2 processor
PLC2 unprotected read
PLC2 unprotected write
1
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Communicating with Other Devices
Caching Messages
Some types of messages use a connection to send or receive data.
Some also give you the option of either leaving the connection open
(cache) or closing the connection when the message is done
transmitting. The following table shows which messages use a
connection and whether or not you can cache the connection:
This type of message:
Using this communication
method:
Uses a
connection:
Which you
can cache:
CIP data table read or write
CIP
X
X
PLC2, PLC3, PLC5, or SLC (all types)
CIP
DH+
X
X
CIP generic
N/A
your option(1)
your option(1)
block-transfer read or write
N/A
X
X
CIP with Source ID
(1)
You can connect CIP generic messages, but for most applications we recommend you leave CIP generic messages unconnected
A cached connection remains open until one of the following occurs:
• The controller goes to Program mode
• You rerun the message as uncached
• Another message is initiated and a cached buffer is needed
• An intermediate node in the connection goes down.
Message Buffers
A Logix5000 controller has buffers for unconnected messages and for
cached messages. Buffers store incoming and outgoing message data
until the controller can process the data.
Unconnected
Buffers
MSG and Block-Transfer
Instructions
3
Incoming
Open/Close Connections
CIP Generic MSG
Unconnected MSG
10 - 40
Outgoing
Communications
Handler
Controller
Connections
Data To and From
Logix5000 Controller
250
Connections
(Buffers)
Uncached Connected CIP MSG or Block-Transfer
Cache Buffers
Cached Connected
MSG or Block-Transfer
16 MSG Buffers
16 BT Buffers
Revision 12 and higher controller firmware allows
32 cached, shared between MSGs and block-transfers
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Communicating with Other Devices
Buffer:
Description:
10 outgoing unconnected buffers
The outgoing unconnected buffers are for:
You can increase this to 40 by using a CIP
Generic message instruction. See the MSG
section in the Logix 5000 Controllers
General Instructions Reference Manual,
publication 1756-RM003
7-3
• establishing I/O connections to local I/O modules and remote devices on
ControlNet, EtherNet/IP, and Universal remote I/O networks
• executing unconnected PLC2, PLC3, PLC5, or SLC (all types) messages over
Ethernet or ControlNet (CIP and CIP with Source ID)
• initiation of messaging over DH+ (uses 2 buffers, one to open the connection and
one to transfer data)
• initiation of uncached block transfers
• initiation of uncached CIP read/write message instructions
• initiation of cached block transfers
• initiation of cached CIP read/write messages instructions
• CIP Generic message instructions
3 incoming unconnected buffers
The incoming unconnected buffers are for:
• initial receiving of a cached CIP message instruction
• receiving an uncached CIP message instruction
• receiving a message over DH+
• receiving a CIP Generic message instruction
• receiving a read or write request from a ControlNet PanelView (unconnected
messaging)
• initial receiving of a read request from an Ethernet PanelView (connected
messaging)
• receiving a write request from an Ethernet PanelView (unconnected messaging)
• receiving a initial request from RSLogix 5000 to go online
• initial receiving of RSLinx connections
16 cached message buffers
16 cached block-transfer buffers
The cached buffers are outgoing buffers for cached messages and cached block-transfers.
A cached connection helps message performance because the connection is left open and
does not need to be reestablished next time it is executed.
If you cache more than 16 messages in either set of buffers, the controller looks at the
current buffers to determine how to deal with the additional cached messages. The
controller will look for a connection that has been inactive for the longest time and close
that connection and allow a new one to take its place. But if all 16 cached connections are
in use, the message will use one of the 10 unconnected out going buffers. If all the
unconnected buffers are in use, the message instruction will error with code 301 (No
Buffer Memory) or 302 (Bandwidth Not Available).
With revision 12 and higher controller firmware, you can cache 32 messages. For optimum
performance, do not cache more than 32 messages. If you cache more than 32 messages,
the controller looks for a connection that has been inactive for the longest time, closes
that connection, and allows a new connection take its place. The controller will close a
cached message or block-transfer, depending on which has been inactive the longest. If all
32 cached connections are in use, the message will use one of the unconnected out going
buffers.
The first time a cached message is executed, it uses one of the 10 out going unconnected
buffers. When the connection is established it will then move into the appropriate cached
buffer area.
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Communicating with Other Devices
In controllers with firmware revision 12 or earlier, the maximum
number of messages you can have active at the same time depends on
the type of message. If you are doing cached block transfers, you
have memory set aside for 16 cached block transfer connections. If
you are doing Logix-to-Logix or other message styles that can be
cached, you have another set of 16 cached connections. You then still
have the 10 unconnected out going buffers to use. So you could have
42 messages active at once.
Using outgoing unconnected buffers
Buffers:
Use:
1-10
The first 10 buffers (default) are shared for unconnected messaging, initiating connected
messaging, establishing I/O connections, and establishing produced/consumed connections.
11
The 11th buffer is dedicated to establishing I/O and produced/consumed connections.
12-40
The 12th to the 40th buffers are used only for initiating connected messages and executing
unconnected messages. To increase the outgoing buffers to a value higher than 11, execute a
CIP generic message to configure that change.
Guidelines for Messages
Message tags must exist as
controller-scoped, base tags
The information in a message tag is accessed by the operating system asynchronously to the
program scan. In addition to the visible fields within the message tag, there are hidden
attributes only referenced by the background operating system.
You can have more than 32
messages in a program
The controller supports 32 active messages at a time. If you determine that there are more
than 32 messages, you will not be able to keep them cached. You will need extra
programming to ensure that no more than 32 messages are active at the same time.
Prior to controller revision 12, the controller supported 16 active messages at a time.
You can use a message to send
a large amount of data
Publication 1756-RM094A-EN-P - May 2004
Even though there are network packet limitations (such as 500 bytes on ControlNet and
244 bytes on DH+), the controller can send a large amount of data from a single MSG
instruction. When configuring the message, select an array as the source/destination tags
and select the number of elements (as many as 32,767 elements) you want send. The
controller automatically breaks the array into small fragments and sends all the fragments to
the destination. On the receiving side, the data appears in fragments, so some application
code may be required to detect the arrival of the last piece.
Communicating with Other Devices
7-5
Guidelines for Managing Message Connections
User-defined structures let you organize your data to match your machine or process.
Create user-defined structures
or arrays
• One tag contains all the data related to a specific aspect of your system. This keeps
related data together and easy to locate, regardless of its data type.
• Each individual piece of data (member) gets a descriptive name. This automatically
creates an initial level of documentation for your logic.
• You can use the structure to create multiple tags with the same data lay-out.
• RSLinx optimizes user-defined structures more than stand-alone tags.
Cache connections when
appropriate
If a message executes repeatedly, cache the connection. This keeps the connection open and
optimizes execution time. Opening a connection each time the message executes increases
execution time.
If a message executes infrequently, do not cache the connection. This closes the connection
upon completion of the message, which frees up that connection for other uses.
Use one message instruction
multiple times for multiple
devices
Each message uses one connection, regardless of how many devices are in the message
path. To conserve connections, you can configure one message instruction to sequentially
read from or write to a different device each time it executes. On each execution, the
instruction breaks its connection from one device and re-establishes the connection to a
subsequent device.
The system overhead timeslice percentage you configure for the
controller determines the percentage of controller time (excluding the
time for periodic and event tasks) that is devoted to communication
and background functions. This includes sending and receiving
messages. For information on specifying a system overhead
percentage, see “Selecting a System Overhead Percentage” on
page 2-10.
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Communicating with Other Devices
Guidelines for Block-Transfer Messages
Distribute 1771 analog modules
across multiple chassis
Isolate different 1771 chassis on
different networks
Increase ControlNet
unscheduled bandwidth
Increase the system overhead
timeslice percentage
Mapping Tags
Distributing 1771 analog modules across multiple chassis reduces the number of
block-transfers that a single 1771-ACN or 1771-ASB module needs to manage.
Isolating different chassis onto different networks diversifies the communications so that no
single network or communication module has to deal with all of the communications.
If communicating over ControlNet, increase the amount of ControlNet unscheduled
bandwidth to permit additional time on the network for data exchange.
Increase the Logix5000 controller’s system overhead timeslice to allocate more CPU time to
communication processing from the continuous task.
A Logix5000 controller stores tag names on the controller so that other
devices can read or write data without having to know physical
memory locations. Many products only understand PLC/SLC data
tables, so the Logix5000 controller offers a PLC/SLC mapping function
that lets you map Logix tag names to memory locations.
• You only have to map the file numbers that are used in
messages; the other file numbers do not need to be mapped.
• The mapping table is loaded into the controller and is used
whenever a “logical” address accesses data.
• You can only access controller-scoped tags (global data).
When mapping tags:
• Do not use file numbers 0, 1, and 2. These files are reserved for
Output, Input, and Status files in a PLC-5 processor.
• Use PLC-5 mapping only for tag arrays of data type INT, DINT,
or REAL. Attempting to map elements of system structures may
produce undesirable effects.
• Use these file types and identifiers:
Publication 1756-RM094A-EN-P - May 2004
For this Logix5000 array type:
Use this PLC file identifier:
INT array
N or B
DINT array
L
REAL array
F
Chapter
8
Optimizing an Application for Motion Control
Introduction
The Logix5000 controller contains a high-speed motion task which
executes motion commands (relay ladder and structured text) and
generates position and velocity profile information. The controller
sends this profile information to one or more motion modules.
RSLogix 5000 programming software provides complete axis
configuration and motion programming support.
For more information on motion, see:
• The Motion Book
• Logix5000 Controllers Motion Instructions Reference Manual,
publication 1756-RM007
• ControlLogix Motion Module Setup and Configuration Manual,
1756-UM006
Coarse Update Rate
The coarse update rate determines the periodic rate at which the
motion task executes to compute the servo commanded position,
velocity, and accelerations to be sent to the motion modules when
executing motion instructions.
To calculate the coarse update rate:
• 2 ∗ (task execution time + number of actions for every axis)
• divide the result by 1000 and round to the nearest msec
If the coarse rate is too small, the controller might not have time to
execute non-motion logic. As a general rule, one millisecond per axis
is required by the motion task in order to allow the controller
reasonable execution time.
The motion planner takes almost its entire minimum coarse iteration
time. The coarse iteration time is minimally set 1 msec per axis. So if
you have a periodic task running every 5 msec and 2 axes of motion,
the motion planner runs twice consuming close to 4 of the 5 msec. In
this case, it’s possible to never finish executing the periodic task.
1
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8-2
Optimizing an Application for Motion Control
Axis Limits
Controller:
Supported Motion Modules and Axes:
Applications:
ControlLogix
1756-M03SE (3 axes)
RA SERCOS drives
1756-L60M03SE (3 axes)
1756-L60 controller with embedded SERCOS interface
RA SERCOS drives
1756-M08SE (8 axes)
RA SERCOS drives
1756-M16SE (16 axes)
RA SERCOS drives
1756-M02AE (2 axes)
RA and third party:
• analog command signal
• quadrature encoder feedback
1756-HYD02
RA and third party:
• analog command signal
• linear transducer feedback
1756-M02AS
RA and third party:
• analog command signal
• SSI feedback
SoftLogix
1784-PM16SE (16 axes)
RA SERCOS drives
• maximum of four 1784-PM16SE cards per computer
• associate only one 1784-PM16SE card with one controller
1784-PM02AE (2 axes)
RA and third party:
• maximum of four 1784-PM02AE cards per computer
• analog command signal
• maximum of four 1784-PM02AE cards can be associated
with one controller
• quadrature encoder feedback
• cannot associate a 1784-PM02AE motion card with the
same controller as a 1784-PM16SE card
Performance Limits
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The motion planner interrupts all other tasks, regardless of priority.
• The number of axes and coarse update period for the motion
group effect 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 rate occurs while a task is executing, the
task pauses to let the motion planner execute.
Optimizing an Application for Motion Control
Motion Event Task Triggers
An event task executes automatically based on a preconfigured event
occurring. There are different motion-based events.
To trigger an event task when: Use this trigger:
registration input for an axis
turns on (or off)
8-3
Axis Registration
1 or 2
With these considerations:
• In order for the registration input to trigger the event task, first execute
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, execute 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.
axis reaches the position that is
defined as the watch point
Axis Watch
• In order for the registration input to trigger the event task, first execute
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, execute 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 coarse update period for the motion group triggers the execution of
both the motion planner and the event task.
• Because the motion planner interrupts all other tasks, it executes first.
If you assign the event task as the highest priority task, it executes
after the motion planner.
For information on configuring an event task, see Chapter 2 “Dividing
Logic into Tasks, Programs, and Routines.”
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Optimizing an Application for Motion Control
Notes:
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Chapter
9
Optimizing an Application for Use with HMI
Introduction
Rockwell Automation offers several HMI (human-machine interface)
platforms:
Platform:
Description:
PanelView Plus
dedicated, machine-level HMI
RSView ME
open, machine-level HMI
RSView SE Station
single-workstation, supervisory-level HMI
RSView SE Distributed
multi-server, multi-client, supervisory-level HMI
RSView32
single-station or single-server, multi-client, supervisory-level HMI
RSLinx software
software products that provide plant-floor device connectivity for HMI applications
includes:
• RSLinx Classic, also known as RSLinx 2.x
• RSLinx Enterprise
Deciding how to implement HMI
Method:
Single HMI
Multiple, Independent HMI
Benefits:
Considerations:
• all HMI/EOI support this method
• single point of failure for visualization
• limited number of controller connections
• no server to setup and manage
• only one person can monitor a single display
at a time
• all HMI/EOI support this method
• more controller connections are required
• the same HMI screens can be viewed at
multiple stations
• additional burden on controller to service all
communications (program scan impact)
• multiple people can monitor different parts of
system simultaneously
• no sharing of data
• each HMI gets its own data
• adding additional HMIs has larger increase
on system
• no server to setup and manage
Client/Server HMI:
• the same HMI screens can be viewed at
multiple stations
• additional server computer to administer
• server collects data for multiple clients
• little communications overhead savings if
each client wants different data
• fewer controller connections required
• impact on system is smaller than with
multiple HMIs
• server is a single point of failure for all HMIs
• adds communications
Most third-party HMIs are limited to direct communications similar to
the multiple HMI method above.
1
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Optimizing an Application for Use with HMI
Guidelines for HMI Applications
On one machine, the maximum is:
Limit the number of servers on
one machine
• one HMI server
• one data server
Configure no more than two HMI servers per application:
Maximum of two HMI servers
per application
• use one computer for each server
• maximum of 20,000 tags per HMI server
Configure no more than two data servers per application:
Maximum of two data servers
per application
• use one computer for each server
Configure no more than 20 HMI clients per application:
Maximum of 20 HMI clients
per application
• RSLinx Classic supports a maximum of 10 HMI clients
• RSLinx Enterprise supports a maximum of 20 HMI clients
See the “Comparison of RSLinx Classic and RSLinx Enterprise“on page 9-5.
Comparison of RSView32 and RSView Enterprise
HMI product:
RSView32
Benefits:
• support Windows NT, Windows 2000, and
Windows XP
Considerations:
• RSView32 only supports development for
PC-based HMIs
• must use PanelBuilder software for PanelView
terminals
RSView Enterprise
• supports Windows 2000 and Windows XP
• single RSView Studio development
environment for PC-based HMIs, PanelView
Plus terminals, and VersaView CE terminals
• FactoryTalk enabled
Publication 1756-RM094A-EN-P - May 2004
• does not support Windows NT
Optimizing an Application for Use with HMI
Important: Unless otherwise indicated,
references to RSLinx software include
both RSLinx Classic software and RSLinx
Enterprise software
RSLinx software acts as a data server to optimize communications to
HMI applications. RSLinx software groups data items into a single
network packet to reduce the number of messages that get sent over
the network and that need to be processed by a controller.
1. When RSLinx software first connects to a Logix5000 controller, it
queries the tag database and uploads definitions for all
controller-scoped tags. If there are multi-layer, user-defined
structures that are controller-scoped, RSLinx software just
queries the upper layer.
2. When the HMI client requests data, RSLinx software queries the
definitions for program-scoped tags and the lower layers of
multi-layer user-defined structures.
3. RSLinx software receives requests for data items from local or
remote HMI/EOI clients and combines multiple requests in
optimized packets. Each data item is a simple Logix tag, array or
user-defined structure. Each optimized packet can be as large as
480 bytes of data and can contain one or more data items.
4. The Logix5000 controller allocates unused system RAM to create
an optimization buffer to contain the requested data items.
– a single optimization buffer can contain as much data as will
fit into a single 480-byte packet (optimization is limited to
480 bytes)
– currently, RSLinx Enterprise only provides optimization for
array tags
– if you use RSLogix 5000 software to monitor controller RAM,
you can see used memory increase
– the controller creates an optimization buffer for each RSLinx
optimization packet in the scan.
Kbytes of Memory Needed
How RSLinx Software
Communicates with
Logix5000 Controllers
9-3
Standalone tags
Optimized
array tags
Tags on Scan in RSLinx
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Optimizing an Application for Use with HMI
Guidelines for RSLinx Software
For multiple HMI stations:
Use RSLinx software as the data
server for multiple HMIs
• leverage remote OPC (RSLinx Classic software) or FactoryTalk (RSLinx Enterprise
software) for data collection
• only the RSLinx data server should have an active topic
• do not configure or use topics on the HMI stations
• RSLinx software does not need to be on the HMI stations
Do not use too many
RSLinx stations
Account for delay time when
adding/removing scanned tags
The performance of tag collection decreases as the more RSLinx stations collect data from
the same controller.
Use an RSLinx Gateway station and have the other data collection stations use remote OPC
for data collection.
When switching from one HMI screen to another, it takes time to put items in the controller
on scan and take items off scan. Part of this time delay is due to the controller allocating
system RAM for the optimization buffer.
To eliminate this delay, when switching between HMI screens, put the items in the HMI
screens on scan and leave them on scan. For example, you can create a data log to keep the
items on scan. Then when switching between HMI screens, data collection continues
without interruption.
RSLinx Enterprise and RSView SE software account for this time delay. When HMI screens
change, these applications deactivate tags rather than remove them from scan.
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Optimizing an Application for Use with HMI
9-5
Comparison of RSLinx Classic and RSLinx Enterprise
Comparison:
RSLinx Classic (RSLinx 2.x) Software:
Supported platforms
RSLinx Enterprise Software:
• Windows 98
• Windows CE
• Windows ME
• Windows 2000
• Windows NT
• Windows XP
• Windows 2000
• Windows XP
Architecture
single-threaded
multi-threaded
Data server
OPC data server
Factory Talk Live data server
preferred data server for PLC/SLC platforms and
applications requiring complex network routings
preferred data server for Logix5000 platforms
maximum 20 clients per data server
maximum 10 clients per data server
PLC/SLC systems
maximum 20 controllers per data server via Ethernet
maximum 20 controllers per data server via Ethernet
Logix5000 systems
maximum:
maximum:
User interface and
event logs
Benefits
• 10 controllers per data server via Ethernet
• 20 controllers per data server via Ethernet
• 10,000 active (on-scan) tags per data server
• 20,000 active (on-scan) tags per data server
• 3 RSLinx data servers per controller
• 3 RSLinx Enterprise data servers per controller
yes
currently no
• supports topic switching with redundant
ControlLogix system
• uses 4 read and 1 write uni-directional
connections (fewer than RSLinx software)
• support used-defined tag optimization
• automatically handles Logix tag changes
• RSLinx Gateway consolidates multiple HMI
requests to reduce network traffic
• FactoryTalk Live consolidates multiple HMI
requests to reduce network traffic
• works with integrated OPC server
Considerations
• requires HMI to be restarted if Logix5000
controller is reloaded with changes to tags on
scan
• does not support topic switching with
redundant ControlLogix system
• uses 4 bi-directional connections
• does not yet support OPC
• optimization limited to array tags
• ActiveX faceplates require a separate
OPC server
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Optimizing an Application for Use with HMI
Guidelines for Configuring Controller Tags
Use INT data types with third
party products
Most third party operator interface products do not support DINT (32-bit) data types.
However, there are additional performance and memory-use considerations when using INT
data types. See “Guidelines for Data Types” on page 3-2.
RSView supports native Logix5000 data types (including BOOL, SINT, INT, DINT, and REAL),
structures, and arrays.
Group related data in arrays
Most third party operator interface products do not support user-defined structures. Arrays
also ensure that data is in contiguous memory, which optimizes data transfer between the
controller and RSLinx or other operator interface.
Arrays of tags transfer more quickly and take up less memory than groups of individual tags.
Map tags to PLC addresses
To optimize data transfer between the controller and RSLinx or other operator interface, use
PLC mapped tags.
The RSLinx topic must have the Optimize Poke Packets enabled.
The RSView application must write the values through a DownloadAll command or the
WritePendingValues VBA method.
Use RSLinx OPC services
Use RSLinx OPC services to bundle multiple tag requests into a single message to reduce
communications overhead.
OPC provides better optimization than DDE.
Referencing controller data from RSView
This table shows how to reference data in RSView tag address.
Logix5000 Array Data Type:
Description:
PLC File Identifier:
RSView Tag Data Type:
INT
16-bit integer
N
Integer
DINT
32-bit integer
L
Long Integer
SINT
8-bit integer
A
Byte
REAL
floating point
F
Floating Point
BOOL
value of 0, 1, or -1
B
Digital
When addressing a Logix5000 string tag, use the address syntax
“[OPC_Topic]StringTag.Data[0],SC82” to address a SINT array. The
string data is stored in the SINT array “.Data” of the string tag, and you
address the first element of this array (“.Data[0]”). The maximum
number of characters in a STRING tag is 82. If you need more
characters than that, create your own user-defined structure to hold
the characters. See “Guidelines for String Data Types” on page 3-10.
Publication 1756-RM094A-EN-P - May 2004
Chapter
10
Optimizing an Application for Process Control
Introduction
The Logix5000 controller integrates a function block diagram editor
and several process control instructions. The controller can generally
execute more loops than typical applications require.
Comparison of PID and
PIDE Instructions
The function block PIDE instruction offers additional enhancements
over the relay ladder PID instruction:
Enhanced PID (PIDE):
Standard PID:
velocity form algorithm which works on change in error value
position form algorithm which works on error values
This algorithm is the same type as used in most DCS systems. The
algorithm also makes it easier to implement adaptive gains.
full set of modes:
limited set of modes
• program/operator control
• auto mode
• cascade/ratio mode
• software manual mode (similar to PIDE manual mode)
• auto mode
• manual mode (similar to PIDE hand mode)
• manual mode
• override mode
• hand mode
available selection of timing modes:
no timing modes
• periodic
• oversample
• real time sampling
handling for PV/CV faults
no handling for PV/CV faults
The PIDE block has built-in PVFault and CVFault members.
full bumpless transfer into and out of cascade mode
1
no bumpless transfer into or out of cascade mode
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10-2
Optimizing an Application for Process Control
Guidelines for Programming PID Loops
Configure the periodic tasks to execute at the desired rate.
Place PID loops in a
periodic task
Estimate the number of PID loops that can be executed as:
Estimate the number of loops
based on task execution time
(execution time of periodic tasks in msec) / 2
This leaves sufficient time for the controller to manage other logic in lower-priority tasks.
Estimating number of loops
The number of loops depends on the execution time of the periodic
task as well as the controller.
Periodic Task Execution Times (msec)
Controller
10
20
40
100
250
500
1000
1756-L55
6
13
26
64
161
322
644
1756-L6x
18
36
72
180
450
899
1799
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Optimizing an Application for Process Control
10-3
Advanced Process
Instructions
Instruction:
Description:
Alarm (ALM)
provides alarming for any analog signal.
Enhanced PID (PIDE)
provides enhanced capabilities over the standard PID instruction. The instruction uses the
velocity form of the PID algorithm. The gain terms are applied to the change in the value of
error or PV, not the value of error or PV.
Ramp/Soak (RMPS)
provides for a number of segments of alternating ramp and soak periods.
Scale (SCL)
converts an unscaled input value to a floating point value in engineering units.
Position Proportional (POSP)
opens or closes a device by pulsing open or close contacts at a user-defined cycle time with
a pulse width proportional to the difference between the desired and actual positions.
Split Range Time Proportional (SRTP)
takes the 0-100% output of a PID loop and drives heating and cooling digital output contacts
with a periodic pulse.
Lead Lag (LDLG)
provides a phase lead-lag compensation for an input signal.
Function Generate (FGEN)
converts an input based on a piece-wise linear function.
Totalizer (TOT)
provides a time-scaled accumulation of an analog input value.
Deadtime (DEDT)
performs a delay of a single input. You select the amount of deadtime delay.
Discrete 2-State Device (D2SD)
controls a discrete device which has only two possible states such as on/off, open/closed,
etc.
Discrete 3-State Device (D3SD)
controls a discrete device having three possible states such as fast/slow/off,
forward/stop/reverse, etc.
Faceplates
The RSLogix 5000 programming software includes faceplates for some
function block instructions. These faceplates are Active-X controls that
read the entire data structure for the associated instruction You can
use these faceplates with RSView software or any other application
that acts as an Active-X container.
IMPORTANT
RSLogix 5000 programming software is not a valid Active-X container.
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Optimizing an Application for Process Control
The faceplates communicate with the controller via the RSLinx OPC
server. The RSLinx OPC server is not available in the RSLinx Lite
software that comes with RSLogix 5000 programming software. You
have to purchase a package such as RSLinx OEM, Professional,
or Gateway.
These instructions have faceplates:
• Alarm (ALM)
• Enhanced Select (ESEL)
• Totalizer (TOT)
• Ramp/Soak (RMPS)
• Discrete 2-State Device (D2SD)
• Discrete 3-State Device (D3SD)
• Enhanced PID (PIDE)
Publication 1756-RM094A-EN-P - May 2004
Glossary
A
Term:
Definition:
atomic data type
BOOL, SINT, INT, DINT, and REAL data types.
B
Term:
Definition:
buffer
A temporary memory area used for queuing incoming and outgoing messages. The buffer area of a
device determines how many messages can be queued for processing.
C
Term:
Definition:
cache
To leave a connection open for a MSG instruction that executes repeatedly.
coarse update rate
Determines the periodic rate at which the motion task executes to compute the servo commanded
position, velocity, and accelerations to be sent to the motion modules when executing motion
instructions.
compound data type
array, structure, and string data types.
connection
A communication link between two devices, such as between a controller and an I/O module,
PanelView terminal, or another controller:
• connections are allocations of resources that provide more reliable communications between
devices than unconnected messages
• you indirectly determine the number of connections the controller uses by configuring the
controller to communicate with other devices in the system
consumed tag
A tag that receives the data that is broadcast by a produced tag over an EtherNet/IP network,
ControlNet network, or ControlLogix backplane. A consumed tag must be:
• controller scope
• same data type (including any array dimensions) as the remote tag (produced tag)
See produced tag.
controller scope
Data accessible anywhere in the controller. The controller contains a collection of tags that can be
referenced by the routines and alias tags in any program, as well as other aliases in the controller
scope.
See program scope.
D
Term:
Definition:
direct connection
A direct connection is a real-time, data transfer link between the controller and an I/O module. The
controller maintains and monitors the connection with the I/O module. Any break in the connection,
such as a module fault or the removal of a module while under power, sets fault bits in the data area
associated with the module.
See rack-optimized connection.
E
1
Term:
Definition:
element
An addressable unit of data that is a sub-unit of a larger unit of data. A single unit of an array or
structure.
explicit
A connection that is non-time critical and is request/reply in nature. Executing a MSG instruction or
executing a program upload are examples of explicit connections. Explicit refers to basic information
(source address, data type, destination address, etc.) that is included in every message.
See implicit.
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2
I
Term:
Definition:
implicit
A connection that is time critical in nature. This includes I/O and produced/consumed tags. Implicit
refers to information (source address, data type, destination address, etc.) which is implied in the
message but not contained in the message.
See explicit.
index
A reference used to specify an element within an array.
L
Term:
Definition:
local connection
A connection to a module in a local chassis, extended-local chassis, or any of the I/O banks configured
for the controller. Communication occurs across the backplane or virtual backplane and does not
require an additional communication module or adapter.
M
Term:
Definition:
member
An element of a structure that has its own data type and name.
• Members can be structures as well, creating nested structure data types.
• Each member within a structure can be a different data type.
N
Term:
Definition:
network update time (NUT)
The repetitive time interval in which data can be sent on a ControlNet network. The network update
time ranges from 2ms-100ms.
P
Term:
Definition:
postscan
A function of the controller where the logic within a program is examined before disabling the program
in order to reset instructions and data.
prescan
Prescan is an intermediate scan during the transition to Run mode.
• The controller performs prescan when you change from Program mode to Run mode.
• The prescan examines all programs and instructions and initializes data based on the results.
• Some instructions execute differently during prescan than they do during the normal scan.
produced tag
A tag that a controller is making available for use by other controllers. Produced tags are always at
controller scope.
See consumed tag.
program scope
Data accessible only within the current program. Each program contains a collection of tags that can
only be referenced by the routines and alias tags in that program.
See controller scope.
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3
R
Term:
Definition:
rack-optimized connection
For digital I/O modules, you can select rack-optimized communication. A rack-optimized connection
consolidates connection usage between the controller and all the digital I/O modules in the chassis (or
DIN rail). Rather than having individual, direct connections for each I/O module, there is one
connection for the entire chassis (or DIN rail).
See direct connection.
remote connection
A connection to a module in a remote chassis or DIN rail. Communication requires a communication
module and/or adapter.
requested packet interval (RPI)
When communicating over a the network, this is the maximum amount of time between subsequent
production of input data.
• Typically, this interval is configured in microseconds.
• The actual production of data is constrained to the largest multiple of the network update time
that is smaller than the selected RPI.
S
Term:
Definition:
scheduled connection
A scheduled connection is unique to ControlNet communications. A scheduled connection lets you
send and receive data repeatedly at a predetermined rate, which is the requested packet interval (RPI).
For example, a connection to an I/O module is a scheduled connection because you repeatedly receive
data from the module at a specified rate. Other scheduled connections include connections to:
• communication devices
• produced/consumed tags
On a ControlNet network, you must use RSNetWorx for ControlNet to enable all scheduled
connections and establish a network update time (NUT).
structure
Some data types are a structure.
• A structure stores a group of data, each of which can be a different data type.
• Within a structure, each individual data type is called a member.
• Like tags, members have a name and data type.
• You create your own user-defined structure, using any combination of individual tags and most
other structures.
• To copy data to a structure, use the COP instruction.
system overhead timeslice
Specifies the percentage of controller time (excluding the time for periodic tasks) that is devoted to
communication and background functions (system overhead):
U
Term:
Definition:
unconnected message
An unconnected message is a message that does not require connection resources. An unconnected
message is sent as a single request/response.
Publication 1756-RM094A-EN-P - May 2004
4
Notes:
Publication 1756-RM094A-EN-P - May 2004
Available Publications
Logix5000 Platform:
Logix5000 Controllers
Publications:
• Logix5000 Controllers Quick Start, 1756-QS001
• Logix5000 Controllers System Reference Manual, 1756-QS107
• 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 Controllers General Instructions Reference Manual, 1756-RM003
• Logix5000 Controllers Process Control and Drives Instructions Reference Manual,
1756-RM006
• Logix5000 Controllers Motion Instructions Reference Manual, 1756-RM007
• Logix5000 Common Procedures Programming Manual, 1756-PM001
• Logix5000 Controllers Import/Export Reference Manual, 1756-RM084G
• Converting PLC-5 or SLC 500 Logic to Logix5000 Logic Reference Manual,
1756-RM085
ControlLogix Controllers
• ControlLogix Controllers Installation Instructions, 1756-IN101
• ControlLogix System User Manual, 1756-UM001
• ControlLogix Motion Module Setup and Configuration Manual, 1756-UM006
CompactLogix Controllers
• 1769-L31 CompactLogix Controllers Installation Instructions, 1769-IN069
• 1769-L32, -L35E CompactLogix Controllers Installation Instructions, 1769-IN020
• 1769-L20, -L30 CompactLogix Controllers Installation Instructions, 1769-IN047
• 1769-L31, -L32E, -L35E CompactLogix System User Manual, 1769-UM011
• 1769-L20, -L30 CompactLogix System User Manual, 1769-UM007
FlexLogix Controllers
• FlexLogix Controllers Installation Instructions, 1794-IN002
• FlexLogix System User Manual, 1794-UM001
SoftLogix Controllers
• SoftLogix Controllers Installation Instructions, 1789-IN001
• SoftLogix System User Manual, 1789-UM002
RSLogix 5000 programming software includes PDF files of these
publications, in addition to online help and a tutorial.
1
Publication 1756-RM094A-EN-P - May 2004
Rockwell Automation
Support
Rockwell Automation provides technical information on the web to assist you
in using our products. At http://support.rockwellautomation.com, you can
find technical manuals, a knowledge base of FAQs, technical and application
notes, sample code and links to software service packs, and a MySupport
feature that you can customize to make the best use of these tools.
For an additional level of technical phone support for installation,
configuration and troubleshooting, we offer TechConnect Support programs.
For more information, contact your local distributor or Rockwell Automation
representative, or visit http://support.rockwellautomation.com.
Installation Assistance
If you experience a problem with a hardware module within the first 24
hours of installation, please review the information that's contained in this
manual. You can also contact a special Customer Support number for initial
help in getting your module up and running:
United States
1.440.646.3223
Monday – Friday, 8am – 5pm EST
Outside United
States
Please contact your local Rockwell Automation representative for any
technical support issues.
New Product Satisfaction Return
Rockwell tests all of our products to ensure that they are fully operational
when shipped from the manufacturing facility. However, if your product is
not functioning and needs to be returned:
Publication 1756-RM094A-EN-P - May 2004 2
United States
Contact your distributor. You must provide a Customer Support case
number (see phone number above to obtain one) to your distributor in
order to complete the return process.
Outside United
States
Please contact your local Rockwell Automation representative for
return procedure.
PN 957867-08
Copyright © 2004 Rockwell Automation, Inc. All rights reserved. Printed in the U.S.A.
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