Lesson 6 - Managing Resources (CAN)

8/13/2019 Lesson 6 - Managing Resources (CAN)

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Lesson 6

Managing Resources

A. Understanding File I/O

B. Understanding High-level

File I/O

C. Understanding Low-level

File I/O

D. DAQ Programming

E. CAN APIs

F. CAN Programming inLabVIEW (Channel API)


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A. Understanding File I/O

File I/O writes to or reads from a file

A typical file I/O operation involves the following process:

Open/

Create/

Replace File

Read

and/or

Write to File

Close

File

Check for

Errors


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A. Understanding File I/OFile Formats

LabVIEW can use or create the following file formats:

BinaryUnderlying file format of all other file formats

ASCIISpecific type of binary file that is a standard used by

most programs LVMThe LabVIEW measurement data file (.lvm) is a tab-

delimited text file you can open with a spreadsheetapplication or a text-editing application

TDMSType of binary file created for NI productsconsisting of two separate files: a binary file and a binaryindex file


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A. Understanding File I/OFile Formats

In this course, you learn about creating text (ASCII) files

Use text files in the following situations:

You want to access the file from another application

Disk space and file I/O speed are not crucial

You must not perform random access reads or writes

Numeric precision is not important


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B. Understanding High-level File I/O

High-level VIs

Perform all three steps (open,read/write, close) for common file I/Ooperations

Might not be as efficient as thefunctions configured or designed forindividual operations

Low-level VIs

Individual VI for each step If you are writing to a file in a loop, use

low-level file I/O functions


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B. Understanding High-Level File I/O

Write to Spreadsheet File Converts an array of double-precision numbers to a text string and

writes the string to an ASCII file

Read From Spreadsheet File Reads a specified number of lines or rows

from a numeric text file and outputs a2D array of double-precision numbers

Write to/Read from Measurement File Express VIs that write data to or read data

from an LVM or TDMS file format


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C. Understanding Low-Level File I/O VIs


8/34GOAL

Exercise 6-1

Spreadsheet Example VI

Use a high-level file I/O VI to write to a spreadsheet-readable

file.


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Exercise 6-2

Temperature Log VI

Modify a VI to create an ASCII file using disk streaming.


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Exercise 6-2

Temperature Log VI

What would happen if you used the Write to Measurement

File Express VI inside the While loop?


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D. DAQ Programming

1. Signal

2. Terminal Block

3. Cable

4. DAQ Device

5. Computer


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D. DAQ ProgrammingBasic Flow

A basic DAQmx application involves the following process:

Configure

Task

Acquire or

GenerateData

Clear

Task

Create

Task

Start

Task


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D. DAQ ProgrammingCreate Task

Create Virtual Channel VI

Creates a virtual channel and adds it to a task

Use pull-down menu to select the appropriate instance of this

VI


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D. DAQ ProgrammingStart Task

Starts the task after the task has been configured


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D. DAQ ProgrammingAcquire or Generate Data

Acquire or generate data from the DAQ device

Make sure pull-down menu selection is compatible with task

configuration


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D. DAQ ProgrammingClear Task

DAQmx Clear Task VI

Stops the task

Releases any resources the task reserved

Clears the task


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D. DAQ ProgrammingExample

Example acquisition with triggering


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E. CAN APIs

Channel API

High level

Easy to use physical units

Easy CAN/DAQ synchronization

Not compatible with NI-CAN 1.6 or lower

Frame API

Lower-level, advanced API

Command/response protocol Advanced CAN/DAQ synchronization

Compatible with all versions of NI-CAN


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E. CAN APIs

You can use only one API at a time per CAN port

For most applications, use Channel API

Use Frame API when:

you require use of remote frames

you have advanced requirements for synchronizing CAN and

DAQ cards

you are using a USB-CAN Interface


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F. CAN Programming in LabVIEW

Link between the functions is the task reference

CAN task

Collection of CAN channels that have identical timing and the

same communication direction read or write Can be several messages, but must all be on the same

interface or port


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F. CAN Programming in LabVIEW


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GOAL

Choose One:

Exercise 6-3

Using DAQmx (DAQ)

or

Exercise C-3

Read and Write CAN Channels (CAN)

6-3: Explore a DAQmx example program that continuously

acquires data, and modify it to wait on a digital trigger.C-3: Read and write channels from the CAN card using the

LabVIEW environment.


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DISCUSSION

Choose One:

Exercise 6-3

Using DAQmx (DAQ)

or

Exercise C-3

Read and Write CAN Channels (CAN)

In Exercise 6-3, what types of VIs did you use outside of the

While Loop? In Exercise C-3, how would modify the VI to acquire from an

additional channel?


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SummaryQuiz

1. Your continuously running test program logs to a single file theresults of all tests that occur in one hour as they are calculated. If

you are concerned about the execution speed of your program,

should you use low-level or high-level File I/O VIs?

a) Low-level file I/O VIsb) High-level file I/O VIs


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SummaryQuiz Answer

1. Your continuously running test program logs to a single file theresults of all tests that occur in one hour as they are calculated. If

you are concerned about the execution speed of your program,

should you use low-level or high-level File I/O VIs?

a) Low-level file I/O VIsb) High-level file I/O VIs


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SummaryQuiz

2. If you want to view data in a text editor like Notepad, what fileformat should you use to save the data?

a) ASCII

b) TDMS


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SummaryQuiz

3. Which of the following conveys the basic DAQmx programmingflow?

a) Create TaskConfigure TaskAcquire/Generate DataStart Task

b) Acquire/Generate DataStart TaskClear Task

c) Start TaskCreate TaskConfigure TaskAcquire/GenerateDataClear Task

d) Create TaskConfigure TaskStart TaskAcquire/Generate

DataClear Task


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SummaryQuiz Answer

3. Which of the following conveys the basic DAQmx programmingflow?

a) Create TaskConfigure TaskAcquire/Generate DataStart Task

b) Acquire/Generate DataStart TaskClear Task

c) Start TaskCreate TaskConfigure TaskAcquire/GenerateDataClear Task

d) Create TaskConfigure TaskStart TaskAcquire/Generate

DataClear Task


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SummaryQuiz

4. Which of the following are ways to access CAN channels in yourCAN application?

a) Specify a channel name that has been imported into MAX

b) Specify a database file and channel name for channels not in MAX

c) Use the CAN Get Names VI to access all channels in a database file


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SummaryQuiz Answers

4. Which of the following are ways to access CAN channels in yourCAN application?

a) Specify a channel name that has been imported into MAX

b) Specify a database file and channel name for channels not in

MAXc) Use the CAN Get Names VI to access all channels in a database

file

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Lesson 6 - Managing Resources (CAN)