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PCI-6534:DATA acquisition on -ve edge of strobe



I need to receive the data from FPGA based circuit.

That PCB will give 8 bits of digital data parallal  along with strobe.

Now my VI should recevie this 8 bit of data only on negative edge of strobe.

No strobe, no receiving of data.

How can i design My VI for this application.

I am having PCI-6534 and Ni-9401 cards.

Which one is better to use and how can i design my VI.

Please give me some suggestions.



Thanks & Regards,


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Hello Ravi,


As you described, that you want to use FPGA also so using a 9401 cRIO Module is a better option. You can use  that module on a cRIO chassis (say 9103,9102 etc) which have a FPGA Backplane. So you can build three VIs for your application:


2. RT VI

3. Windows Host VI 


You can use FIFOs to communicate between FPGA and RT VIs.



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Hi Ravi,


I wanted to suggest that you can use The Cont Read Dig Chan-Ext example from the Example Finder (Help>>Find Examples) for this measurement. You can locate this example under Hardware Input and Output>>DAQmx>>Digital Measurements. This is set to read in data based on an external clock. You can specify the lines to read and the line you are using for your clock. You can also create a constant for the DAQmx Timing VI for the Active Edge input in order to read on the falling edge of the clock signal. While the VI should be compatible with either hardware you mentioned in your post, the 9401 only has 8 DIO lines which would mean you would need to use another module to handle the clock. Using the 6534 you may notice that you are reading back data in chunks of 32 bits if you are trying to read more often than 32 bits have been acquired. This would be due to the DMA transfer, which means that the data is transferred to memory without needing the processor to execute the command. The other option is to use Interrupts as the data transfer mechanism and I have included some links to more information about the data transfer below.  


The 6534 Help would be useful to look at if you choose to use it. There a a few sections that you should note such as the Generating and Receiving Digital Patterns and Waveforms—Sample Clock section, the Selecting the Sample Clock Active Edge section, and the Configuring the Sample Clock section. These are located under the Sample Timing Types heading. The DMA section of the help file can be found under Data Transfer>>Choosing a Data Transfer Method and will describe the data transfer sizes for the specified data width.


Interrupt Driven Transfers Using an External Clock with a PCI-6534


Configuring the Data Transfer Mechanism (Interrupts or DMA) in DAQmx and Traditional DAQ


NI 6533/6534 for NI-DAQmx Help

Steve B

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