VISA read problem

[YvesM_91]

Hi everyone,

I am using LabVIEW 2023 Q3 32 bits and I want to communicate with a COM port using the VISA functions. It used to work in the past but something may have changed and I can't figure out what.

When I use a VISA read command, I receive the correct answer from my instrument as long as I don' ask long databytes. I want to read 65536 bytes and I receive only 4096 whatever the timeout I put.

[santo_13]

Please attach your code (in LV2019 or earlier) and more detail of your instrument to guide you better.

[crossrulz]

When I need to read more than 4k of data, I tend to read in chunks.  This is simply a VISA Read inside of a FOR loop.

[YvesM_91]

unfortunately, my LV code is only in LV2023 now.

[YvesM_91]

My LV code worked fine in previous versions with 64 kB of data and it is not working well now.

The software dedicated to the instrument works fine but with LV I can address several instruments/motors... and make some scans.

Do we need to clear the buffer before addressing a new command ? I am wondering if remaining data in the buffer would cause my problems

[santo_13]

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@YvesM_91 wrote:

unfortunately, my LV code is only in LV2023 now.

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All that you have to do is goto File menu, select save for previous version and select 19.0

https://www.ni.com/docs/en-US/bundle/labview/page/saving-for-a-previous-version.html

[YvesM_91]

I hope it is ok now for reading in LV2019

[YvesM_91]

Now I put a VISA I/O buffer to 65536 but the VISA read command does only read 3741 bytes (it should read 65534).

Why is so ?

[santo_13]

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@YvesM_91 wrote:

I hope it is ok now for reading in LV2019

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You didn't attach anything

[santo_13 · Accepted solution]

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@YvesM_91 wrote:

Now I put a VISA I/O buffer to 65536 but the VISA read command does only read 3741 bytes (it should read 65534).

Why is so ?

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Potentially the data contained the termination character and hence VISA treated the data is complete.