DAQMx Write und read function

Hello,
I want to use DAQMx functions for my projekt.. but I do not understand one thing. Wenn I have a differnet Input should I use DAQmx write and for the Output DAQMX Read? or better said what is the different betwen DAQmx write and Read, When I can used write and read?

Hi nichts,
use the DAQmx read function, if you want to acquire a signal from your card. If you use a differential input, you also use the same vi (DAQmx read) and change the "input terminal configuration" on the DAQmx Create virtual channel vi to differential mode.
If you want to generate data from your PC and output those data over your DAQ-Card, use the DAQmx write VI.
If you use the DAQmx driver the first time, I would recommend you the following internet page:
Learn 10 Functions in NI-DAQmx and Handle 80 Percent of Your Data Acquisition Applications - Developer Zone - National Instruments
http://www.ni.com/white-paper/2835/en
You will find all necessary information about the important part of the DAQmx driver on this page.

Similar Messages

VISA Read function Read buffer problem in serial communication

Hi, I use VISA write and read function in serial communication app, the device continuously sends 0x00 if it is not receive a request from Labview program running on PC.
And the request sent by labview is programmable. I met a weird problem, each time the request changes, the VISA read buffer output port still shows the last request firstly, from second time, shows the right request.
It works like: Req code: ... 50, 51,51,51,50....; VISA Read buffer: ...50, 50, 51, 51, 51, 51, 50....
Please refer to the program.
Attachments:
readOne_test.vi ‏21 KB

How are you running this? You don't have a while loop around it. Is it part of a larger VI? Please don't tell me you are using the run continuously button.
You don't have any wait statement between you VISA Write and your bytes at port. So it is very likely the receive buffer is still empty since you didn't give your VI time to wait for the device to turn around and give a reply. If you read 0 bytes, your VISA read string will be empty. How does your decoder subVI (which you didn't include) handle an empty string?

DAQmx write shown as broken, read fine

I'm trying to bring a test up-to-date, it was originally in 8.6 and I've brought it into 11, also I can't work on it on the system where it runs. (it's heavily utilized)
I've exported and imported the MAX settings from the old system to my system
the VI shows the broken arrow and says the DAQmx write is broken, however if I open the DAQmx write it doesn't show the broken arrow and works fine, no errors.
I tried deleting and reapplying the call to the DAQmx but I get the same error, reads don't have the problem.
I also tried opening a new project, same results, VI with DAQmx write shows the broken arrow, DAQmx doesn't
the original app writes to a NI PCI-6250 which I don't have in the my system, If I do a DAQ Assit the 6250 shows up, which in my mind means the import of the MAX settign has worked, device also shows up in MAX, but the DAQ assit VI is also marked as broken by the VI.
using LabView 2011 SP1 and DAQmx 9.4, win 7 is the OS
anyone have a idea of what I'm doing wrong?
Solved!
Go to Solution.

Try right-clicking on the DAQmx write VI on the block diagram and select Open Polymorphic VI. This will show you all the instance VIs and flag the ones that are broken.
Mike...
Certified Professional Instructor
Certified LabVIEW Architect
LabVIEW Champion
"... after all, He's not a tame lion..."
Be thinking ahead and mark your dance card for NI Week 2015 now: TS 6139 - Object Oriented First Steps

DAQ vi to perform digital write and read measurements using 32 bits binary data saved in a file

Hi
DAQ vi to perform digital write and read measurements using 32 bits binary data saved in a file
Two main
sections:
1)
Perform
write and read operations to and fro different spread sheet files, such that
each file have a single row of 32bits different binary data (analogous to 1D
array) where the left most bit is the MSB. I don’t want to manually enter the
32 bits binary data, I want the data written or read just by opening a file
name saves with the intended data.
      2)
And
by using test patterns implemented using the digital pattern generator or build digital data functions or otherwise, I need to
ensure that the
            binary data written to a spreadsheet file or any supported file type
then through the NI-USB 6509 is same as the data read.
I’m aware I can’t use the simulated
device to read data written to any port but if the write part of the vi works I
‘m sure the read part will work on the physical device which I’ll buy later.
My Plan
of action
I’ve
created a basic write/read file task and a write/read DAQ task for NI USB 6509
and both combine in a while loop to form a progress VI which I’m confuse of how
to proceed with the implementation.
My
greatest problem is to link both together with the correct functions or operators
such that there are no syntax/execution errors and thus achieve my intended
result.
This
project is one of my many assignments for my master thesis, so please i’ll
appreciate every help as I’m not really efficient with LabVIEW programming but
I prefer it because is fun and interesting if I get to know it.
Currently I’m
practicing with LabVIEW 8.6/NI DAQmx 8.8 Demo versions and NI USB 6509
simulated device.
Please see
the attached file for my novice progress, thanks in
advance for the support
Rgds
Paul
Attachments:
DIO_write_read DAQ from file.vi ‏17 KB

What does your file look like? The DAQmx write is expecting a single U32 value, not an array of I64.
Message Edited by vt92 on 09-16-2009 02:42 PM
"There is a God shaped vacuum in the heart of every man which cannot be filled by any created thing, but only by God, the Creator, made known through Jesus." - Blaise Pascal

Error-50150 occured at DAQmx Write

Hello,
I am experiencing a seemingly random error in a large program. The error occurs in a part of the program that simulates tach signals to a CPLD. I have not been able to find out what conditions cause this error, it seems to be random in nature.
The full error reads this:
Error - 50150 occurred at DAQmx Write(Digital 1D U16 1Chan Nsamp).vi
Possible Reasons:
The software has entered an unknown state-usually as a result of a cascade failure induced by an unexpected series of state inputs. The operation could not be completed as specified and you should immediately terminate all further transactions if you are able to do so.
Task Name:TackABC_Write Port0 U16
The device we are using is a PCI-DIO-32HS, with Labview 7.1, NI-MAX 4.1, and DAQmx drivers 8.3.1. The task writes 3 signals to the CPLD, and it works most of the time, but every so often this error will occur. I was wondering what could be the cause of an error like this?
Thanks, Steve

Hello Brian, thanks for the response.
I made a mistake in my last post, it is actually a DAQmx clear task in place of the stop task vi i mentioned. When we first received this error it had no clear task at the end, but I added one. Even with this the error has still shown up from time to time. Would it help at all to add a reset device vi afte the clear task vi?
I took some screenshots for you as well. The first shot is of the function in question, the second is the same shot with the case turned to false, and the third is the inside of the main subvi. When the error occurs it focuses on the write vi that is inside the subvi. Let me know if there is more info I could grab that would make things mroe clear.
Thanks,
Steve
Attachments:
SS3.JPG ‏160 KB
SS1.JPG ‏189 KB
SS2.JPG ‏181 KB

DAQmx Write - Append samples to buffer

I'm developing a program to play back a waveform from a large file on disk. This is 72 hours of 1kHz data on 4 channels. I can't load the entire waveform into memory, so I wanted to feed the DAQ task 1 minute at a time. I figured that I would read in a minute of file data, convert it to a waveform, and then write it to the DAQ task. While that one minute is being sent out, I can read in the next minute and convert it and have it ready to load into the DAQ task.
The problem is that the DAQmx Write function has two "Relative To" options, "First Sample" and "Current Sample". Given my idea above, I'd expect that there would be a "Last Sample" option as well so I could just tack on the next block of data to the end of the currently playing sample.
I need to avoid any glitching on the line. I'm not sure if a simple write in a loop will be fast enough to copy the new data to the DAQ buffer. I don't have my hardware yet, but I'd like to have the basics of my application set up so I can plug in the hardware on the day it gets here. But I don't want any nasty suprises that would cause me to completely restructure my software.
Are there any other functions that I could look at in order to accomplish my goal?
Brian Rose

Hi Brian,
I am not sure what devices you are using, version of DAQmx and LabVIEW you are using but I have some ideas that hopefully will help you out. First off, I wanted to reference you to an example in the NI Example Finder that I was using for testing. The example is called "Cont Gen Voltage Wfm-Int Clk-Non Regeneration.vi" and can be found by Help>>Find Examples>>Hardware Input and Output>>DAQmx>>Analog Generation>>Voltage. This example is what you should base your code off of because it continually writes samples to the buffer every iteration. Make sure though to set the "Relative To" DAQmx write vi to "current write position". This needs to be added when you are setting up the generation in the DAQmx write property node. This setting will write the data to the end of the buffer and not overwrite your waveform. Also, you will need to change your waveform you are writing to the DAQmx Write vi to the waveform you are reading from the file. It sounds though that you already have this portion set up.
Regards,
Jordan F
National Instruments

Closing a serial port after executing a for loop of write and reads.

Hello,
Labview is opening and then closing each write to the port. I have tried to leave the close outside of the for loop, but labview wont allow it. What do I need to change to make all the writes and reads execute on 1 open and close of the serial port.?
Thanks.
Attachments:
Controller.vi ‏27 KB

J_es--
The program that you posted looks to be ok for the most part, you might consider putting an open after your configure (but that's trivial). The other thing that is a minor issue is the loop tunnel coming out of your for loop is currently being auto-indexed. This function is used to index data for each interation of the loop. You are using a static address (not an array) and so you don't need this. If you right-click and remove the auto-index the broken wire will go away. Other than that it should be ok.
I would suggest looking at one of the shipping examples that come with LabVIEW. "Basic Serial Read and Write" is essentially the same thing that you are doing and is tested here and might save you a bit of time. Anyway, take a look if you have a second. Best of luck with your application!
John H.
Applications Engineer
National Instruments
http://www.ni.com/support

Adobe Acrobat X: Attachments and Extended Reader Functions...

All,
after adding attachments (e.g. PDF documents) to a PDF document and saving the document with "Extended Reader Functions" an error is shown in the Java debugger window:
SyntaxError: missing ) after argument list
10:Document-Level:ADBE::FileAttachmentsCompatibility
Adobe creates a document-level javascript function called "FileAttachmentsCompatibility" within ADBE.
Looking into the source code, the error can be easily seen
app.alert("Dieses Dokument hat Dateianlagen. zum Anzeigen der Anlagen klicken Sie auf "Speichern", um eine Kopie des...
(a part of the German version is shown)
As one can see, the highlighting "Speichern" (saving) is inside of double quotation marks.
This can only be solved by - again - saving the newly created document as a copy. Opening this document, one can edit the faulty script
Find below the corrected version:
var v = app.viewerVersion;
if (v < 7)
var n = 0;
if (this.dataObjects != null)
n = this.dataObjects.length;
if (v >= 5 && v < 6 && n > 0 && (app.viewerVariation == "Full" || app.viewerVariation == "Fill-In"))
if (this.external)
   app.alert("Dieses Dokument hat Dateianlagen. Zum Anzeigen der Anlagen klicken Sie auf "Speichern", um eine Kopie des Dokuments zu speichern. Öffnen Sie die Kopie in Adobe Acrobat, und wählen Sie "Datei" > "Dokumenteigenschaften" > "Eingebettete Datenobjekte".", 3, 0);
else
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if (n == 0)
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   syncAnnotScan();
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    var annots = this.getAnnots(p);
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The script was automatically created by the Adobe Acrobat software...
I know the issue, but is there any bug-fix available? I don't want to correct it for every document!
Correction: Above you find the automatically created document.
A corrected possibility is shown below:
var v = app.viewerVersion;
if (v < 7)
var n = 0;
if (this.dataObjects != null)
n = this.dataObjects.length;
if (v >= 5 && v < 6 && n > 0 && (app.viewerVariation == "Full" || app.viewerVariation == "Fill-In"))
if (this.external)
   app.alert("Dieses Dokument hat Dateianlagen. Zum Anzeigen der Anlagen klicken Sie auf 'Speichern', um eine Kopie des Dokuments zu speichern. Öffnen Sie die Kopie in Adobe Acrobat, und wählen Sie 'Datei' > 'Dokumenteigenschaften' > 'Eingebettete Datenobjekte'.", 3, 0);
else
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if (n == 0)
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How can i write and read the same data

hi,
         i have attached my program to this mail. i have some problems in this program.
problems:
1. I want to select the threshold for the rms,varience and s.d.
But what i used is not doing that. i want to fix the upper threshold value and lower threshold value.
when ever the input crosses upper threshold value i want the output and it will remains uptill the value above the lower threshold value.
Once it come down the lower threshold value the output should be stopped.
2. I want to write this in to a file and i want to read this file. is this possible or not.
            please try to help me i am very new with lab view6i
       REGARDS
CHAMARTHY KOMAL DILEEP.
   [email protected]
Attachments:
dileep.vi ‏93 KB

The easiest way to perform a certain action (such as file I/O) based on a certain condition (such as whether a value has passed a certain threshold) is to use a comparison VI in combination with a case structure. Then you can specify that if your rms, standard deviation and variance are above a threshold then perform a certain action.
Also consider using shift registers to keep track of data from the last loop. If I understand you correctly, you want to start logging data when an upper threshold has been passed. Then you want to continue logging data until a lower threshold is passed. I have attached a non-functional but explanatory VI that will help explain how to implement logic to that effect. It also demonstrates that you can indeed write and read from the same file in a loop. The best way to do this is to open the file before the loop, do all the necessary writing and reading in the loop, and then close the file after the loop.
Hope this helps!
Jarrod S.
National Instruments
Attachments:
dileep_example.vi ‏61 KB

NI 6602 Write and Read Frequency

Hi all ,
I Have NI 6602 timing card and i'm trying to use it in order to write and read using the
DAQmxWriteCtrFreq (taskHandle1, 0, 1, 10.0, DAQmx_Val_GroupByChannel, &freq, &duty, &writtenVal, 0);
and
DAQmxReadCounterScalarF64(taskHandle2,10.0,&dataVal,0);
what i'm trying to do is to write to ctt0 and to read from ctr7 ( they are crossed in the card )
i'm having a bit problems with that can some one give me a tip on how to do it properly ?
just write freq to ctr0 and read freq from ctr7.....
Kobi Kalif
Software Engineer
Solved!
Go to Solution.

You should have the following sample installed on your PC that may help you in this task: DigPulseTrain-Cont.prj (it could be located in \program files\National Instruments\CVIx\samples\daqmx\counter\generate pulse folder)
Proud to use LW/CVI from 3.1 on.
My contributions to the Developer Zone Community
If I have helped you, why not giving me a kudos?

Error -200609 occurred at DAQmx Write: Selected Buffer Size Too Small

Hello, I'm writing some simple test VI's that I will eventually build upon to make an externally clocked analog output VI. I started with a very simple program to output finite samples using the onboard clock with the DAQmx Timing.VI. When I run the program, I almost immediately get an error. The error message is below.
Error -200609 occurred at DAQmx Write (Analog DBL 1Chan 1Samp).vi:1
Possible reason(s):
Generation cannot be started, because the selected buffer size is too small.
Increase the buffer size.
Conflicting Property
Property: Output.BufSize
Corresponding Value: 1
Minimum Supported Value: 2
Task Name: _unnamedTask<1C>
I have used DAQmx VI's before in similar applications and never encountered this error. Additionally, I read at the link below that DAQmx Timing.VI should be generating the buffer automatically. Any ideas as what could be causing this?
Specs:
Windows 7
Labview 2012
PCIe-6353 as DAQ board
Below is a picture of my block diagram and the VI is attached.
Solved!
Go to Solution.
Attachments:
FiniteSamplesTest.vi ‏18 KB

Oops. Just realized my very silly mistake: I forgot to add the Start Task VI. I did so and it works as designed.

Use virtual channel name as input to DAQmx Write? LV8 and DAQmx

I've created a task for digital output that contains 8 named channels using the DAQmx Create Channel VI in Labview. Is it possible to use the channel name as an input to the DAQmx Write VI to reference the desired channel? I tried wiring a string with the channel name to the "task/channels in" input but I get a -200428 error that says the Value passed to the Task/Channels In control is invalid.
The help "name to assign" input for the DAQmx Create Channel VI says
If you use this input to provide your own names for the virtual channels, you must use the names when you refer to these channels
in other NI-DAQmx VIs and Property Nodes
OK, so how do you use the name assigned in other VIs?
George

George,
I think that there may be some confusion here about the difference between local and global virtual channels. First of all, please take a look at the following knowledge base:
Physical Channels, Virtual Channels, and Tasks in NI-DAQmx
As discussed in this KB, local global channels are created inside a task, and they only apply to that task. In the help file for the DAQmx Write VI, the "task/channels in" description says "if you provide a list of virtual channels, NI-DAQmx creates a task automatically." When you wire a string to this input, a new task is being created, and unless the channel name that you wire in is a global virtual channel (listed in MAX), you will get the error 200428 that you mentioned. This is because that virtual channel that you are specifying is local to another task and is not associated with this new task.
One solution to this issue is to use the DAQmx Save Global Channel VI to save your local virtual channel as a global virtual channel before calling DAQmx Write. Once this is done, you can then wire the same string constant to the "task/channels in" input of DAQmx Write or other DAQmx VI's.
The help text is still correct, but is only applicable in certain situations. For example, if you create and name an analog input local virtual channel with DAQmx Create Channel, you could then use this channel name as the source input to a DAQmx Trigger VI configured for an analog edge start trigger. You could also use that channel name as the input to the "ActiveChans" DAQmx Channel Property, which would enable you to modify the properties of that particular channel.
Hopefully this information is helpful to you.

Warning 200015 occurred at DAQmx Write (Digital Wfm 1Chan NSamp).vi:4

Hi,
Attached is the VI I write. But there is a warning: Warning 200015 occurred at DAQmx Write (Digital Wfm 1Chan NSamp).vi:4
I want to use digital channel to create an output. The duty cycle change from 30% to 50% to 70%. At the same time, measure the input of another 2 channels.
Do you have any idea about this?
Thanks.
Attachments:
Digital pulse_DO Channel-1_mod2.vi ‏39 KB

Hello,
The situation that you are seeing here can be identified as 'glitching'. Glitching occurs where there is potential for previous samples in a buffer to be mixed in with newer samples written into the buffer, causing a signal output that is a mix between the old and new data you are trying to output. In the DAQmx Help document, search for 'glitching' and you will be directed to an article which explains glitching, mentions Warning 200015 is thrown where there is a potential for this to happen, and then offers suggestions on how to work around this issue, as well as two pictures that clarifies what could happen with glitching.
This warning pops up in your application since you are writing one set of data and then writing a second set of data afterwards. If you do not see glitching on your signal, you can modify your code to ignore this warning. Read through the help document for suggestions on modifications that will work for your application.
Kyle A.
National Instruments
High Speed Digital I/O Product Support Engineer - R&D

Erreur -200245 s'est produite à DAQmx Write

Bonjour,
J'ai un système PXI-1042 avec plusieurs cartes (PXI-6221, PXI-6533...) et surtout 2 cartes de generation analogique PXI-6713. Le chassis est piloté via controleur MXI-4 déporté dans un PC.
Nous creons des sequences qui durent 2-3sec avec echantillonage de 1ms et nous générons ces sequences en boucle. Nous stoppons la génération, changeons un paramètre et relancons l'execution de la sequence. De temps en temps, nous avons le message d'erreur suivant : "L'erreur -200245 s'est produite à : DAQmx Write. Raisons possibles : Measurements : La PLL a perdu son verrouillage par rapport à l'horloge de référence externe.... "
Je vous ai mis en doc attaché une image de la capture d'ecran avec le message d'erreur.
Je dois alors arreter le VI puis le relancer pour que la sequence soit lancée sans message d'erreur. Cette erreur arrive aléatoirement, parfois rien pendant plusieurs jours et parfois plusieurs fois par jour...
Quelqu'un pourrait il me donner quelques explications concernant ce message d'erreur afin d'optimiser mon application.
Merci d'avance
Attachments:
bug1.jpg ‏421 KB

Bonjour,
Merci pour votre réponse, je n'avais pas trouvé le premier lien sur le site de NI qui me semble correspondre à mon problème.
>> Why do I receive Error -200245 with my X Series Card?
Nous n'utilisons pas d'horloge externe donc j'aurais tendance à croire que l'erreur vient de cette remarque : Signal generation: The reference clock signal should be active before calling starting any DAQmx task that will attempt to use the reference clock. Ensure that your reference clock source is generating the clock prior to DAQmx Start Task being called.
Si je comprends bien, il semblerait que ce soit du à une erreur de synchronisation de l'horloge PLL. C'est à dire que quand on lance l'acqui, il y a une horloge qui est créée pour synchroniser les cartes d'acqui, et pour cela, elle utilise l'horloge du fond de panier du châssis PXI. (on n'utilise pas d'horloge externe). Cette horloge référence est créée à chaque fois qu'on lance la génération et est libérée à chaque arrêt. Il semblerait qu'on lance la tache avant que l'horloge soit prête.
Il est possible que ce soit dû au fait que l'on va trop rapidement entre arrêter une séquence et lancer la suivante.
Je vais voir si il y a des astuces de prog pour interdire le lancement du DAQmx Start Task tant que le PLL n'est pas prêt, peut etre avez vous des infos à ce niveau? Validez vous mes hypothèses précédentes?
Merci beaucoup pour votre aide.

How to write and read data in a specific memory location ??

Hi Everyone:
Does anyone know how to write and read data in a specific memory location by using Java ?
I need pointers, but I don't know how to do it ??
Thanks for answering
Rodger

Hi Everyone:
Does anyone know how to write and read data in a
specific memory location by using Java ?
I need pointers, but I don't know how to do it ??
Thanks for answering
RodgerWith Java you cannot write to a specific memory location. Java does not have pointers. If you really want to do it, you need to use JNI, i.e write the required functions in C (or other languages that support pointers) and make those functions available to Java (through JNI). This approach is not portable. You can have a look at http://java.sun.com/docs/books/tutorial/native1.1/index.html
Regards.

DAQMx Write und read function

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