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  • uSD access

    I have 9 uLCD-32PT with PICASO-SGC (using uLCD-32PT-I-LR-SGC-R22.PmmC) connected to a USB hub through uUSB-CE5 connectors and USB cables.

    Each uLCD has a 2G uSD card.

    In each uSD there are 2 small files (in FAT part).

    My program (in python) sends the command "Read File from Card (FAT) - @61hex" to read file content and sometimes the device replies that the size of the requested file is 0 (meaning the file doesn't exist or is empty) whereas the file exists and contains data.

    Do I miss something to do ? Why this happends only "sometimes" ?

    Thanks,

  • #2


    Check that the displays are all getting 5v and not something lower.

    When the voltage 'browns out' the uSD cards are the first to fail.

    Even if the hub was powered I imagine it would struggle to power 9 displays at once
    Mark

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    • #3
      When I connect just 1 uLCD on a laptop, the pb also happens (sometimes):
      - the device replies that the size of requested file is 0 (whereas not)
      - the device sends corrupted data as first file data (like "*$\'")
      - the device blocks while reading file data.

      Comment


      • #4


        Check the quality of your USB cable, many of the 'light weight' ones cannot supply the power required to drive the displays.
        Mark

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        • #5


          Hello,

          I change my USB cables and I split my uLCDs:
          - 4 on a hub,
          - 5 on another hub,

          And I still have the problem,
          - sometimes the file on FAT are not found (or empty)
          - sometimes the first byte of file data is corrupted.

          My program could work one day without problem but at one moment, the problem happens. Do you have an idea why ?

          Comment


          • #6


            Keep checking power, as I said, the uSD cards are the first to go 'funny' with unreliable power.

            Are the hubs powered? What are they rated at?
            Mark

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            • #7


              Hello,
              The hubs are powered. I'm using this one :
              http://www.trust.com/products/product.aspx?artnr=16131
              and this one :
              http://www.ldlc-pro.com/fiche/PB00073510.html (sorry this page is in french)

              If you think the problem is from hubs, can you give me a reference of hub that you use in your test please ?
              Thanks,

              Comment


              • #8


                Sorry we can't reccomend any particular hub.

                The fact that the 'error rate' goes up significantly when you use multiple displays would indicade a power problem.

                However, when reading all your posts again I'm not confident that you really said the error rate with multiple displays is much more than with a single display.

                Try getting it working properly with just one display, it should really go for weeks without problems. Maybe there is something odd with your python script?
                Mark

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                • #9


                  FYI,
                  We solve the problem by replacing all USB cables and uUSB-CE5 converters by 4D Programming cables and it works fine.

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