Showing results for 
Search instead for 
Did you mean: 

Reading and writing from CRio 9074

Hi Everybody,


I know this can't be this difficult, but I have been having a terrible time trying to get this to work :


I am trying to read thirty channels from a 9205 module (5 Hz required sampling) and write the values to a SD card on the 9802 module. I have struggled at this for days and still cannot get it to work. I have attached the FPGA and Host VI to this post. Could somebody please look over them and see what Imight be missing, or write me small example FPGA and Host VIs please?


I greatly appreciate your help!


Download All
0 Kudos
Message 1 of 5

I apologize for sounding blunt but do you understand what you have programmed? Why are you reading values from the FPGA into RT and then writing it back to the FPGA when you can directly transfer the values within the FPGA?


I would recommend you open up Example Finder (Help -> Find Examples) and then navigate to the compactRIO Module Specific directory (show in the attached image) to understand how exactly to program Analog Input and File Input and Output using the 9205 and 9802 respectively. Once you understand this, go into the FPGA Fundamentals directory and open the FIFOs directory to understand how to communicate between loops.


I would also recommend that you get this to work with one channel and then scale the application to accommodate more channels. If you have any questions, be sure to post back.

Adnan Zafar
Certified LabVIEW Architect
Coleman Technologies
Message 2 of 5

Thanks Adnan. I did try writing the values directly within the FPGA itself and it works fine for one channel, but it fails compile if i try to do that for more than one because of timing issues (the execution speed drops well below 40 MHz). I tried using a derived clock instead but I couldn't get that to work.

Another reason I had the values read in the host vi and written back to the fpga vi was because I only need 5Hz worth of data but I did not know how to do that from the FPGA directly. 

Like I said, I have been at this for days and have tried a lot of different options. I am certainly not as knowledgable about these things as any of you are, but I am not stupid and I am not being lazy either. I just really need help at this point and that's why I am here. 

 I will try to look up the help sources you suggested (I already have most of it) - but if you could write a small example fpga vi that reads multiple channels and writes to a SD card (even just in words on this post) I would appreciate it. 


0 Kudos
Message 3 of 5

P.S That wasn't a rant and I am not offended or anything 🙂 The problem with the FPGA programming is there are a lot of little things that can make or break a VI. You have to be a novice to appreciate how frustrating that can be. I will try to look up more of those help sources. I do appreciate your help and guidance. 


0 Kudos
Message 4 of 5

Hi Dhasa,


Have a look at the following forums post:

Writing to SD card on 9802 from FPGA vi


If you have any questions, be sure to post back.

Adnan Zafar
Certified LabVIEW Architect
Coleman Technologies
0 Kudos
Message 5 of 5