National Instruments NI USB-621x User Manual

Chapter 9 Counters
NI USB-621x User Manual 9-18 ni.com
The counter increments on each rising edge of channel A. The counter
decrements on each rising edge of channel B, as shown in Figure 9-19.
Figure 9-19. Measurements Using Two Pulse Encoders
For information about connecting counter signals, refer to the Default
Counter/Timer Pinouts section.
Two-Signal Edge-Separation Measurement
Two-signal edge-separation measurement is similar to pulse-width
measurement, except that there are two measurement signals—Aux and
Gate. An active edge on the Aux input starts the counting and an active edge
on the Gate input stops the counting. You must arm a counter to begin a
two edge separation measurement.
After the counter has been armed and an active edge occurs on the Aux
input, the counter counts the number of rising (or falling) edges on the
Source. The counter ignores additional edges on the Aux input.
The counter stops counting upon receiving an active edge on the Gate input.
The counter stores the count in a hardware save register.
You can configure the rising or falling edge of the Aux input to be the active
edge. You can configure the rising or falling edge of the Gate input to be
the active edge.
Use this type of measurement to count events or measure the time that
occurs between edges on two signals. This type of measurement is
sometimes referred to as start/stop trigger measurement, second gate
measurement, or A-to-B measurement.
Single Two-Signal Edge-Separation Measurement
With single two-signal edge-separation measurement, the counter counts
the number of rising (or falling) edges on the Source input occurring
between an active edge of the Gate signal and an active edge of the Aux
signal. The counter then stores the count in a hardware save register and
ignores other edges on its inputs. Software then reads the stored count.
Ch A
Ch B
Counter Value 2 3 54344

National Instruments NI USB-621x Specifications

General

Model	NI USB-621x
Category	Computer Hardware
Interface	USB
Analog Input Resolution	16 bits
Analog Input Sample Rate	250 kS/s (aggregate)
Analog Output Channels	2
Analog Output Resolution	16 bits
Digital I/O Channels	8
Counter/Timers	2
Operating System Compatibility	Windows, Linux
Power Supply	USB powered
Device Type	Data Acquisition Device
Analog Input Channels	16 single-ended or 8 differential
Analog Input Range	±10 V
Operating Temperature	0 °C to 50 °C

Summary

Chapter 1 Getting Started

Installing NI-DAQmx

Details on installing the NI-DAQmx software, including step-by-step instructions for setup and configuration.

Installing the Hardware

Non-software-specific information for installing USB DAQ devices.

Chapter 2 DAQ System Overview

Programming Devices in Software

How to program DAQ devices using NI-DAQ driver software, functions, and VIs.

Chapter 3 Connector Information

I/O Connector Signal Descriptions

Details the signals found on the I/O connectors, including AI, AO, and PFI signals.

Chapter 4 Analog Input

Analog Input Ground-Reference Settings

Describes supported ground-reference settings (DIFF, RSE, NRSE) for analog input.

Multichannel Scanning Considerations

Issues to consider for accurate multichannel scanning, such as settling time and channel order.

Analog Input Data Acquisition Methods

Explains software-timed vs. hardware-timed acquisitions and buffered vs. non-buffered modes.

Analog Input Digital Triggering

Details the support for start, reference, and pause triggers for analog input.

Analog Input Timing Signals

Summarizes the various timing signals used for analog input operations.

Getting Started with AI Applications in Software

Guidance on using M Series devices for analog input applications in software.

Chapter 5 Connecting AI Signals on the USB-6210/6211 Devices

Connecting Floating Signal Sources

How to connect floating signal sources, including when to use differential or single-ended configurations.

Connecting Ground-Referenced Signal Sources

How to connect ground-referenced signal sources and common connection configurations.

Using Differential Connections for Floating Signal Sources

Diagrams and explanations for differential connections with floating signal sources.

Using Non-Referenced Single-Ended (NRSE) Connections for Floating Signal Sources

Chapter 6 Connecting AI Signals on the USB-6215/6218 Devices

Chapter 7 Analog Output

Analog Output Data Generation Methods

Explains software-timed vs. hardware-timed generations for analog output.

Analog Output Digital Triggering

Details the support for start and pause triggers for analog output operations.

Analog Output Timing Signals

Chapter 8 Digital I/O

I/O Protection

Connecting Digital I/O Signals

Getting Started with DIO Applications in Software

Chapter 9 Counters

Counter Input Applications

Frequency Measurement

Explains various methods for measuring frequency using the device's counters.

Counter Output Applications

Details applications for counter outputs, including pulse and train generation.

Counter Timing Signals

Counter Triggering

Describes arm start, start, and pause triggers for counter operations.

Duplicate Count Prevention

Chapter 10 PFI

Using PFI Terminals as Timing Input Signals

Exporting Timing Output Signals Using PFI Terminals

Using PFI Terminals as Static Digital I/Os

Chapter 11 Isolation and Digital Isolators

Chapter 14 Triggering

Triggering with a Digital Source

How to generate triggers using digital signals, specifying source and edge.

Appendix B Troubleshooting

Analog Input

Analog Output

Appendix C Technical Support and Professional Services

Support