Rockwell Automation Allen-Bradley ControlLogix 1756-HSC User manual

ControlLogix High-speed
Counter Module
Catalog Number 1756-HSC
User Manual Original Instructions

2Rockwell Automation Publication 1756-UM007E-EN-P - August 2021
ControlLogix High-speed Counter Module User Manual
Important User Information
Read this document and the documents listed in the additional resources section about installation, configuration, and
operation of this equipment before you install, configure, operate, or maintain this product. Users are required to familiarize
themselves with installation and wiring instructions in addition to requirements of all applicable codes, laws, and standards.
Activities including installation, adjustments, putting into service, use, assembly, disassembly, and maintenance are required to
be carried out by suitably trained personnel in accordance with applicable code of practice.
If this equipment is used in a manner not specified by the manufacturer, the protection provided by the equipment may be
impaired.
In no event will Rockwell Automation, Inc. be responsible or liable for indirect or consequential damages resulting from the use
or application of this equipment.
The examples and diagrams in this manual are included solely for illustrative purposes. Because of the many variables and
requirements associated with any particular installation, Rockwell Automation, Inc. cannot assume responsibility or liability for
actual use based on the examples and diagrams.
No patent liability is assumed by Rockwell Automation, Inc. with respect to use of information, circuits, equipment, or software
described in this manual.
Reproduction of the contents of this manual, in whole or in part, without written permission of Rockwell Automation, Inc., is
prohibited.
Throughout this manual, when necessary, we use notes to make you aware of safety considerations.
Labels may also be on or inside the equipment to provide specific precautions.
WARNING: Identifies information about practices or circumstances that can cause an explosion in a hazardous environment, which
may lead to personal injury or death, property damage, or economic loss.
ATTENTION: Identifies information about practices or circumstances that can lead to personal injury or death, property damage,
or economic loss. Attentions help you identify a hazard, avoid a hazard, and recognize the consequence.
IMPORTANT Identifies information that is critical for successful application and understanding of the product.
SHOCK HAZARD: Labels may be on or inside the equipment, for example, a drive or motor, to alert people that dangerous voltage
may be present.
BURN HAZARD: Labels may be on or inside the equipment, for example, a drive or motor, to alert people that surfaces may reach
dangerous temperatures.
ARC FLASH HAZARD: Labels may be on or inside the equipment, for example, a motor control center, to alert people to potential Arc
Flash. Arc Flash will cause severe injury or death. Wear proper Personal Protective Equipment (PPE). Follow ALL Regulatory
requirements for safe work practices and for Personal Protective Equipment (PPE).

Rockwell Automation Publication 1756-UM007E-EN-P - August 2021 3
Table of Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Summary of Changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Who Should Use This Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Additional Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Chapter 1
Module Features Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
What is a High-speed Counter Module? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Encoder and Sensor Compatibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1756-HSC Module Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Additional I/O Module Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1756-HSC Parts Illustration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Chapter 2
Counter Modes Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Counter/Encoder Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Counter Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Encoder Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Preset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Rollover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Input Z (Gate/Reset) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Storage Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Assign Outputs to Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Output Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Chapter 3
Frequency Modes Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Frequency Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Frequency Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Sample Period for Frequency Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Period Rate and
Continuous Rate Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Sample Period for Period/Continuous Rate Modes. . . . . . . . . . . . . . 29
Output Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Period Rate /Continuous Rate Output Examples . . . . . . . . . . . . . . . . . . . 32
Maximum Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4Rockwell Automation Publication 1756-UM007E-EN-P - August 2021
Table of Contents
Chapter 4
Install and Wire the
ControlLogix High-speed
Counter Module
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Install the Module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Key the Removable Terminal Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Wiring the Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Connect the Wires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Connect Ungrounded End of the Cable . . . . . . . . . . . . . . . . . . . . . . . . 41
Two Types of RTBs (each RTB comes with housing) . . . . . . . . . . . . . 41
Recommendations for Wiring Your RTB . . . . . . . . . . . . . . . . . . . . . . . 42
Wire Terminations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Wire an Allen-Bradley 845 Incremental Encoder . . . . . . . . . . . . . . . . 42
Wire an Allen-Bradley Bulletin 872 3-Wire DC Proximity Sensor . 43
Wire a PHOTOSWITCH® Series 10,000 Photoelectric Sensor . . . . 44
Assemble the Removable Terminal Block and Housing. . . . . . . . . . . . . . 45
Install the Removable Terminal Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Remove the Removable Terminal Block . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Remove the Module from the Chassis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Chapter 5
Configure the Module Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
ControlLogix Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Direct Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Local Chassis Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Remote Chassis Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Use the Default Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Use the Programming Software, Version 18 or Later,
to Configure a Module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Communication Format Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Set RPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Set Up Counter Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Filter Selections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Set Up Output Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Copy Configuration (.C) Output, Rollover, Preset Tags
to Output (.O) Tags. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Electronic Keying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Exact Match. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Compatible Keying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Disabled Keying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Download Configuration to the 1756-HSC Module. . . . . . . . . . . . . . . . . . 71

Rockwell Automation Publication 1756-UM007E-EN-P - August 2021 5
Table of Contents
Chapter 6
Module Diagnostics Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
1756-HSC Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Programming Software Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Fault Type Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Troubleshoot the Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Appendix A
Status Indicators Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Status Indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Appendix B
Data Structures Configuration, Output, Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Configuration Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Output Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Input Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Appendix C
Module History Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Profile Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Configure a Generic Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Copy ACD file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Add Ladder Logic Routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Upgrade Module to Software Version 18 and Later . . . . . . . . . . . . . . 92
Edit Thin Profile Tags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Change Configuration Data Via Message Instruction. . . . . . . . . . . . . . . 94
Appendix D
Application Considerations Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Types of Input Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Examples for Selecting Input Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Circuit Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Detailed Circuit Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
5V Differential Line Driver Example . . . . . . . . . . . . . . . . . . . . . . . . . . 100
+12 to +24V Single-ended Driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Open Collector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Electromechanical Limit Switch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

6Rockwell Automation Publication 1756-UM007E-EN-P - August 2021
Table of Contents
Output Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Series A and B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Series C and D. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Application Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Input Cable Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Totem-pole Output Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Cable Impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Cable Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Cable Length and Frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

Rockwell Automation Publication 1756-UM007E-EN-P - August 2021 7
Preface
This manual describes how to install, configure, and troubleshoot your
ControlLogix® High-speed Counter (HSC) module, catalog number 1756-HSC,
herein referred to as the module.
Based on your module series and firmware revision, there are programming
software requirements to use some module features. For more information,
see Table 10 on page 83.
Summary of Changes This table contains the changes that are made to this revision of
the publication.
Who Should Use This Manual You must be able to program and operate a ControlLogix controller and
various Allen-Bradley®encoders and sensors to use your module efficiently. In
this manual, we assume that you know how to use these products. If you do
not, refer to the related user publications for each product, before you attempt
to use the module.
Additional Resources These documents provide information that is related to your module.
You can view or download publications at http://
www.rockwellautomation.com/literature. To order paper copies of technical
documentation, contact your local Allen-Bradley distributor or Rockwell
Automation sales office.
Topic Page
Updated Appendix D, Application Considerations , in the following sections:
• Circuit Overview, Series C and D Modules 97
• Detailed Circuit Analysis, Series C and D Modules 99
• +12…+24V Single-ended Driver 100
• Open Collector, Series C and D Modules 103
• Electromechanical Limit Switch 103
• Output Circuits, Series C and D Modules 105
Resource Description
1756 ControlLogix I/O Technical Data, publication 1756-TD002 Provides specifications for the ControlLogix controllers, I/O modules, specialty modules, chassis, power
supplies, and accessories.
ControlLogix System User Manual, publication 1756-UM001 Detailed description of how to use your ControlLogix
operating system.
ControlLogix Digital I/O Modules User Manual,
publication1756-UM058 Detailed description of how to install and use
ControlLogix digital I/O modules.
ControlLogix Analog I/O Modules User Manual,
publication 1756-UM009 Detailed description of how to install and use ControlLogix analog I/O modules.
RSLogix 5000® Getting Results Guide,
publication 9399-RLD300GR.Provides software installation instructions and to learn
how to navigate the software package.
Industrial Automation Wiring and Grounding Guidelines,
publication 1770-4.1 Provides general guidelines for installing a Rockwell
Automation industrial system.

8Rockwell Automation Publication 1756-UM007E-EN-P - August 2021
Preface
Notes:

Rockwell Automation Publication 1756-UM007E-EN-P - August 2021 9
Chapter 1
Module Features
Introduction The high-speed counter module performs high-speed counting for industrial
applications. This chapter provides an overview of the design and features of
the module.
What is a High-speed
Counter Module?
The module counts pulses by using a Counter or Frequency operational mode.
The counts are presented as either ‘accumulated count’ or ‘frequency’
depending on the mode that is configured for the module.
You can choose from either one of three Counter modes or one of three
Frequency modes when configuring the module. The operational mode that is
selected determines how the pulse count is stored and the behavior of the
outputs.
You can manipulate the storage of the count values (detailed in Chapter 2). The
module evaluates these count values against user configured presets and/or
values, thus the response time for activating outputs is performed at a faster
rate than evaluating in the controller.
Configuration tags, which are automatically installed with the module during
the initial download of the programming software, determine whether the
module interprets pulses as:
• accumulated count - values can be 1…16 million.
• frequency - positive or negative depending on the direction of the
rotation.

10 Rockwell Automation Publication 1756-UM007E-EN-P - August 2021
Chapter 1 Module Features
Pulse count values can be calculated by using different types of Counter and
Frequency modes. The simple counter uses only input A to count pulses. An
encoder uses both input A and input B to count pulses. The relationship
between the two channels is how the encoder determines if the count is
positive (clockwise) or negative (counterclockwise).
This user manual also details the Frequency operational modes that are
available depending on which one is required for your application. Frequency
can be calculated in one of three ways:
• frequency (rate measurement).
•periodrate.
• continuous rate.
All three Frequency modes determine the frequency of input pulses by
counting pulses over a user-defined time interval. If the revolution is spinning
in a clockwise direction, the frequency is positive; in a counterclockwise
direction it’s decreasing (negative) frequency.
See page 25 for more details on Frequency modes.
Pulse counts and frequency values are stored in one of three input tags (based
on the mode) as shown in the table.
See Data Structures in Appendix C for a list of tags.
Table 1 - Mode and Input Tag Values for the 1756-HSC Module
Comm Format = HSC Data-extended Tags
Mode Mode Description Present Value Stored Value Totalizer
0Counter
Accumulated count Stored value Directional frequency(1)
1EncoderX1
2EncoderX4
3CounterNotUsed— ——
4Frequency
(Rate Measurement)(2) No. of input pulses occurring in
sample period
Frequency
Accumulated count(3)
5Frequency
(Period Rate)(2) No. of 4 MHz pulses occurring in
sample period Accumulated count
6Frequency
(Continuous Rate)(2)
(1) B-input state defines direction (Counter mode).
(2) Modes where frequency controls the outputs.
(3) Rollover/Preset settings apply.

Rockwell Automation Publication 1756-UM007E-EN-P - August 2021 11
Chapter 1 Module Features
Encoder and Sensor
Compatibility
The most common applications that use the ControlLogix® high-speed counter
module also use these Allen-Bradley®products:
• Allen-Bradley 845 incremental encoder
• Allen-Bradley Bulletin 872 three-wire DC proximity sensor
• PHOTOSWITCH®series 10,000 photoelectric sensor
Additional encoders and sensors can be connected to and used with the
module. For specific compatibility of other encoder and sensor compatibility,
check the user publications for each product or consult your local Allen-
Bradley representative.
The table shows the type of encoder or sensor that you can choose for your
module.
1756-HSC Module Features This table highlights features of the module.
Additional I/O Module Features
This table lists additional features for ControlLogix® I/O modules, including
the 1756-HSC module.
Pulse Width, Min Frequency Range Leakage Current
Proximity 500 ns 1 MHz 250 A @ 5V DC
Quad Encoder 2 s 250 kHz 250 A @ 5V DC
Feature Description
Real-time manipulation of preset/
rollover tag settings
Preset and Rollover tags, which provide a reference point to start the count and
reset the count to zero, respectively, are included in the Configuration tags at
the initial system configuration. The module also has both tags in the Output tag
settings to allow the values to be changed in real time when the 1756-HSC Data-
extended Comm Format is selected. This feature provides the flexibility of
changing counter settings ‘on-the-fly’ without having to reconfigure all system
tags.
Period rate / Continuous Rate
frequencies
Both Frequency modes are available with the 1756-HSC module when using the
Data-extended Comm Format. Period Rate mode counts internal 4 MHz clock
pulses over a used-defined time frame to determine frequency. Continuous
Rate mode is similar to Period Rate mode except dynamic outputs can be
turned On /Off at pre-determined pulse intervals.
Module-specific tags Tags are automatically created when you add a 1756-HSC module to your controller project. The module has descriptive tags for using pulse and
frequency values, such as Present Value, Stored Value, and Totalizer.
Feature Description
Configuration software The programming software has a custom interface to configure your module. All
module features can be enabled and disabled through the software.
Module fault reporting
I/O modules provide both hardware and software indications when a module
fault occurs. Status indicators signal fault conditions. The programming
software describes the fault message so you know what action to take to
resume normal operation.
Status indicators
Status indicators on the front of the module report the operational status of the
module. The input-point status display indicates a particular point’s status,
including specifics for the input A, B, and Z (reset) points for each channel of the
module. The output-point status display indicates the status of four output
points on the module.

12 Rockwell Automation Publication 1756-UM007E-EN-P - August 2021
Chapter 1 Module Features
1756-HSC Parts Illustration
See page 41 for details on RTB types.
Producer/Consumer model
Logix 5000™ controllers let you produce (broadcast) and consume (receive)
system-shared tags. The module can produce data without having to be polled
first by a controller. The module produces the data and any owner-controller
can decide to consume it.
Electronic Keying See page 66 in Chapter 5 for details.
RIUP
RIUP is an abbreviation for removal and insertion under power. The module can
be inserted and removed from the chassis while power is applied. This flexibility
allows you to maintain the module, either removing or inserting, without
disrupting the rest of the controlled process.
Feature Description
7
4
5
6
3
2
1
Item Description
1Backplane connector - The backplane interface for the ControlLogix system connects the module to
the backplane.
2Top and bottom guides - Guides assist in seating the removable terminal block (RTB) onto
the module.
3Connector pins - Input/output, power, and grounding connections are made to the module through
these pins with the use of an RTB.
4Status indicators - Indicators display the status of communication, module health, and presence of
input/output devices. Use these indicators to help in troubleshooting.
5 Locking tab - The locking tab anchors the RTB on the module, maintaining wiring connections.
6Slots for keying - The slots let you mechanically key the RTB to help prevent inadvertently making
the wrong wire connections to your module.
7Removable terminal block - The RTB lets you connect and house the wiring. There are several types
of RTBs.

Rockwell Automation Publication 1756-UM007E-EN-P - August 2021 13
Chapter 2
Counter Modes
Introduction This chapter describes the Counter modes for the 1756-HSC module.
Topics include:
• types of counting: counter and encoder.
• means of storing the counts.
• modes for manipulating the count.
• tags for control of onboard outputs.
There are three Counter modes that can be selected from the Operational
Mode pull-down menu on the Counter Configuration tab. See Chapter 5 for
configuration details.
The choices are:
• Counter mode (default).
•Encoderx1mode.
•Encoderx4mode.
Counter/Encoder Overview The Encoder and Counter modes are virtually identical; the only difference is
the method that is used to count. There are two counters (using input A and B)
per module. Input Z, which is described in more detail later in this chapter,
basically affects how the counts are stored based on the selected Storage mode.
In Counter mode, the module reads incoming pulses from input A only and
stores the accumulated count value in the Present Value tag. The state of
input B determines whether to increment or decrement the count based on
whether it’s low, floating (count up) or high (count down).

14 Rockwell Automation Publication 1756-UM007E-EN-P - August 2021
Chapter 2 Counter Modes
In both Encoder modes, the module uses two channels to read incoming
pulses. The module uses the phase relationship between inputs A and B to
determine the count value and direction of the rotation.
• Encoder x1- This is a Bidirectional Count mode, counting up or down,
using an incremental encoder with direction output.
• Encoder x4 - This is a Bidirectional Count mode, using quadrature
encoder signals, with four times the resolution of X1.
The module also offers the convenience of showing directional frequency by
using any Counter mode. If the count value is increasing, the frequency is
positive in the Totalizer tag. If the count value is decreasing, the frequency is
negative in the Totalizer tag.
There are several methods for using and manipulating the count values. Based
on the state of the Z-input, the module provides four modes of behavior if the
application requires storage of the accumulated count value.
•Store and Continue Mode
•Store, Wait, and Resume
•Store and Reset, Wait, and Start
•Store and Reset, and Start
In addition, the module features two software-configurable tags that provide
control of the starting and ending points of an accumulated count sequence.
These are the tags:
•Preset
•Rollover
The remainder of this chapter details each mode and the different
configurations that you can use for specific needs of your module.
Table 2 - Where Count Values are Stored in Tags
Mode Description Present Value Tag Stored Value Tag Totalizer Tag
Counter
Accumulated Count Stored Value Directional FrequencyEncoder x1
Encoder x4

Rockwell Automation Publication 1756-UM007E-EN-P - August 2021 15
Chapter 2 Counter Modes
Counter Mode
Counter mode is the module’s default operational mode that counts incoming
pulses using input A. You can control the starting and ending points of the
accumulated count depending on how you have configured the module.
In the Counter mode, the count increases or decreases based on the state of
input B, which can be a random signal. If input B is high, the counter counts
down. If input B is low or floating (that is, not connected to a voltage source),
the counter counts up. Counting is done on the leading edge of input A.
Input Z is used in Counter mode only if a Store Count mode is enabled.
See page 20 for details on the Storage modes.
Counter Mode
Input B Direction of Counter
High Down
Low or floating (not connected) Up
Single-phase Pulse Generator
Count Up Count Down
1756-HSC Module
Increment/Decrement Count
Input A
Input B
Input A
Input B
+–
... 1 2 3 012
Accumulated Count in
Present Value Tag
Positive Frequency Negative Frequency
Directional Frequency in
Totalizer Tag
Input Z (optional)
Pulse Count
...

16 Rockwell Automation Publication 1756-UM007E-EN-P - August 2021
Chapter 2 Counter Modes
Encoder Mode
Encoder mode also counts incoming pulses. However, the phase relationship
between two input channels (A and B) determines whether the direction of the
count is up or down.
In Encoder x1 mode, an increasing count results when channel B is 90° ahead
of channel A. The count is initiated on the rising edge of channel A, and the
direction of the encoder is clockwise (positive).
The module produces a decreasing count when channel A is 90° ahead of
channel B. The count is initiated on the falling edge of channel A, and the
direction is counterclockwise (negative).
By monitoring both the number of pulses and the phase relationships of
signals A and B, you can accurately determine the position and direction of the
rotation.
The illustration shows the phase relationships between channels A and B for
the x1 mode. Input Z is used in Encoder mode only if a Store Count mode is
enabled. See page 20 for details on the Storage modes.
Encoder x1 Mode
Encoder
Input A
Input B
Input A
Input B
B Leads A 90° A Leads B 90°
Input A
Input B
123 210
1756-HSC Module
Change
Accumulated Count in
Present Value Tag
Directional Frequency in
Totalizer Tag Positive Frequency Negative Frequency 4488
. . .
Input Z (optional)

Rockwell Automation Publication 1756-UM007E-EN-P - August 2021 17
Chapter 2 Counter Modes
Encoder x4
Encoder x4 mode is identical to x1, except this mode counts on the leading and
trailing edges of A and B to provide a greater number of pulse counts.
The greater the number of pulse counts the better the module can determine
position.
Input Z is used in Encoder mode only if a Store Count mode is enabled.
See page 20 for details on the storage modes.
Encoder x4 Mode
Maximum frequency in Encoder x1 and x4 modes = 250 kHz (assuming
50% duty cycle), with a minimum pulse width at this frequency of 2 s.
The module assumes a 90° phase (A/B°) difference between channels.
Input A
Quadrature Encoder 1756-HSC Module
Input B
Input A
Input B
Input A
Input B
B Leads A 90° A Leads B 90°
1 2 3 4 5 6 7 8 9 10 11 12 1234567891011 0
41689
Accumulated Count in
Present Value Tag
Directional Frequency in
Totalizer Tag Positive Frequency Negative Frequency
Input Z (optional)

18 Rockwell Automation Publication 1756-UM007E-EN-P - August 2021
Chapter 2 Counter Modes
Preset
Each of the two counters has one preset value that is associated with it. In the
Encoder or Counter modes, the preset value represents a reference point (or
value) from which the module begins counting. The module can count either
up or down from the preset value.
The preset value itself is entered during module configuration. However, you
must enter a preset command from either the programming software or
ladder logic before it becomes active. Setting the Preset Enable Bit in the
Output tag to ‘1’ sends the preset value to the Present Value tag.
Preset values are entered on the Counter Configuration tab of the Module
Properties dialog box.
See page 60 for an example of the Counter Configuration tab.
Preset in Output tag
When using the HSC Data-extended Comm Format while configuring the
module, the Preset tag is found in both the Configuration and Output tag
areas.
The Configuration tag value is populated during software configuration with
the Logix 5000™ controller, and sent to the module upon power-up, defining
its behavior. This value continues to define module behavior as long as the
corresponding tag in the output area is zero.
If the value of the Preset tag in the output area is changed to a nonzero value,
the module disregards the value that is sent from the configuration area and
use the value in the output area instead. This facilitates easier real-time ‘on-
the-fly’ changes to the preset function.

Rockwell Automation Publication 1756-UM007E-EN-P - August 2021 19
Chapter 2 Counter Modes
Rollover
Each of the two counters has one rollover value that is associated with it. When
the accumulated count value in the Rollover tag reaches the rollover value, it
resets to zero (0) and begins counting again. The rollover value is circular.
For example, if the rollover value = 360, the count will be from 358, 359, 0, 1, and
so forth, in a positive direction and from 1, 0, 359, 358, and so forth, in a
negative direction.
Rollover values are entered on the Counter Configuration tab of the Module
Properties dialog box in the programming software or can be changed in
ladder logic.
See page 60 for an example of the Counter Configuration tab.
Rollover in Output tag
When using the HSC Data-extended Comm Format while configuring the
module, the Rollover tag is found in both the Configuration and Output tag
areas.
The Configuration tag value is populated during software configuration with
the Logix 5000 controller, and sent to the module upon power-up, defining its
behavior. This value continues to define module behavior as long as the
corresponding tag in the Output area is zero.
If the value of the Rollover tag in the Output area is changed to a nonzero
value, the module disregards the value that is sent from the Configuration area
and use the value in the Output area instead. This facilitates easier real-time
‘on-the-fly’ changes to the Rollover function.
Input Z (Gate/Reset)
Input Z, when active, will change the behavior of an accumulated count value
in the Present Value tag, depending upon which of four modes are selected.
•Store and Continue Mode
•Store, Wait, and Resume
•Store and Reset, Wait, and Start
•Store and Reset, and Start
The Storage modes are selected on the Counter Configuration tab on the
Module Properties dialog box of the programming software.

20 Rockwell Automation Publication 1756-UM007E-EN-P - August 2021
Chapter 2 Counter Modes
Storage Modes
The store count feature lets the module store the current count value and
follow four behavioral paths, depending on which Store mode is selected. The
store count is triggered by the state of the Z-input (the gate) on the module.
The following illustrations show how the different modes store count values in
the Present Value and Stored Value tags.
Store and Continue Mode
In the Store and Continue mode, the module:
• reads the Present Value and places it into the Stored Value on the leading
edge of Input Z.
• continues to accumulate the Present Value based on presets and
incoming pulses.
• retains the Stored Value until new data from the next leading edge of a
pulse on Input Z overwrites it.
Store, Wait, and Resume
IMPORTANT The four modes can be changed while normal module
operation continues. Improper use of on-the-fly changes
may cause unintended machine operation when the store
count is used as a trigger for machine sequencing.
...10
Stored Value Tag in
Logix Controller
Present Value Tag in
Logix Controller
Z-Input
4490
11 12 13 14 15 16 17 18 19 20
...881313131313181818
Incoming Pulses 10 11 12 13 14 15 16 17 18 19 20
44901
Present Value Tag in
Logix Controller
Stored Value Tag in
Logix Controller
Z-Input
10
...
11
11
11 11
11 11
12 13 14 14 14 15 16
11 11 14 14 14 14 14
Incoming Pulses 10 11 12 13 14 15 16 17 18 19 20