Archived: Number of Concurrent Tasks on a NI cDAQ-9172

Publish Date: Feb 05, 2018 | 0 Ratings | 0.00 out of 5 | Print

Overview

This document has been archived and is no longer updated by National Instruments.

This article explains how many different tasks can run concurrently on a single cDAQ-9172, presuming you have one or more modules in your NI cDAQ-9172.

Table of Contents

  1. Introduction
  2. Hardware Timed Tasks
  3. Software Timed Tasks
  4. Additional Resources

1. Introduction

Because hardware timed tasks typically use more onboard resources than software timed tasks, the total number of concurrent tasks typically depends on whether you are running tasks that use hardware timing or software (on demand) timing.

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2. Hardware Timed Tasks


Hardware timed tasks require timing information from the System Timing Controller for sample clocks, reference clocks, triggers, etc. The System Timing Controller for the cDAQ-9172 is the STC2. The STC2 chip on the cDAQ chassis has the following timing engines built in: 1 AI Timing Engines, 1 AO Timing Engine, 0 DI Timing Engines, 0 DO Timing Engines, and 2 general purpose counters. The following table illustrates the number of hardware timed tasks available to the user.

 

Hardware Timed Tasks # of Tasks per Chassis # of Tasks per Module
Analog Input 1 1
Analog Output 1 1
Counter Input 2 2
Counter Output 2 2
Correlated Digital Input 1 1
Correlated Digital Output 1 1

 

Note: Analog output tasks are limited to 16 hardware timed channels.

There is also a streaming buffer for hardware timed tasks that limits the total number of hardware timed tasks that can run simultaneously. The NI cDAQ-9172 supports four data streams. These independent, high-speed data streams allow for up to four simultaneous hardware timed tasks, such as analog input, analog output, buffered counter/timers, or correlated digital input/output.

 

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3. Software Timed Tasks


Most software timed tasks do not require a signal from the STC2 in order to run. Software timed means the host computer is controlling how often a sample is read from or written to the cDAQ module.

Software timed tasks also do not use the data streaming buffer, so there is no four task limit for software timed tasks. However, software timed Analog Input tasks will still use one of the AI timing engines, so the limit for AI tasks is always 1. This is not the case for AO. Subsequently,  the software timed task limits for these types of acquisitions depends on the number of channels you have available to use. Specifications for the number of software timed digital tasks depend on which digital modules you use. For more information see Software Support for CompactRIO, CompactDAQ, Single-Board RIO, R Series, and EtherCAT. See the table below for a summary of software timed tasks using the cDAQ-9172:

 


Software Timed (On Demand) Tasks
# of Tasks on 8-Slot Chassis # of Tasks per Module

Analog Input

 

1

 

1

 

Analog Output

Number of total AO channels in chassis (up to 128 total tasks)

 

1 Task for each channel (up to 16 tasks per module)

 

Digital Input

Please see pages 35-39 of the cDAQ-9172 User Guide and Specifications

 

Please see pages 35-39 of the cDAQ-9172 User Guide and Specifications

 

Digital Output

Please see pages 35-39 of the cDAQ-9172 User Guide and Specifications

 

Please see pages 35-39 of the cDAQ-9172 User Guide and Specifications

 

 

Note: If any AO channel on a module is used in a hardware timed (waveform) task, no channels on that module can be used in a software timed task.

The number of counter tasks is always limited by the fact that you have 2 counters. Depending on whether you are using a counter task that uses 2 counters (like measuring frequency using the two counter methods), you may be restricted to only 1 counter task. However, typically you can have both counters on the cDAQ-9172 running simultaneously in two different tasks. To determine if you need one or two counters for your counter task, see the following KnowledgeBase.

For more information on running tasks on the cDAQ-9172, please reference the cDAQ-9172 User Guide and Specifications.

 

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4. Additional Resources

 

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