Real-Time Measurement and Control

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ni-9401 "release data lines"

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I am using the cRio-9012 with 8 ni 9401 modules in the chassis. I have two of those modules that are connected to an 16 bit data lines. These data lines are used for both input and output. I can write input data to the device connected to 9401 modules. The device responds by setting data on these lines is there a way to release the inputs to allow the connected device to control the data lines. I am not using all of the ni 9401 modules in the chassis. If there is a way to release the lines then I can wire the unused modules to read the data. My software version is Labveiw 8.5
 
thaks
Tony
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Hi Tony,
 
Please clarify what you are trying to achieve--are you trying to eliminate having to use the data lines between teh devic and the modules?
 
Ipshita C.
National Instruments
Applications Engineer
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I'm trying to do data communication between the cRIO and my device. I need to read and write to the same 16 data lines. When I write to the data lines the values 1 or 0 is held until I do another write. I need to set the data lines wait a 10 clock pulses the releases the 16 data lines to allow my device to write data on the lines. thanks Tony
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Hi Tony,
 
From what I understand, you are trying to make your modules bidirectional so that they can accept both input and output, thereby preventing you having to do writes every time you want to do a read. The 9401 is a bidirectional module and be configured for bidirectional line measurements using four-bit nibble. You can have all input, all ouput or one nibble as input and the others as ouput--basically combine them whichever way you want. Please refer to this knowledgebase article on how to configure the nibble bits. Hope this helps.
 
Ipshita C.
National Instruments
Applications Engineer
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Yes that is what I'm trying to do I didn't describe my problem well. When the NI 9401 is configured for output it provides the 5 volt TTL high signal providing the source. After I write the data with the Ni 9401 configured as a digital output is there a way to disable the source? The digital output is holding the data lines to the previous write values and when I read the same data lines with a different ni 9401 module set as an digital input I recieve the data that I just wrote. I have tried turning the ni 9401 set as digital output to input after I write the data but switching between the input and output is to slow. Is there a different module or software/hardware solution that can do this? I apologize for not describing the problem better. thanks Tony
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Hi Tony,

From my understanding you are trying to use one module to read and the other to write. That should not present any problems.

Ipshita C.

National Instruments
Applications Engineer
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