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Problem with FAT16 formatted 4GB uSD card

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  • Problem with FAT16 formatted 4GB uSD card

    I am using FAT16 formatted 4GB uSD card. In the 4DGL user manul, it is mentioned that the picasso GLCD will support uSD card up to 4GB formatted with FAT16. But in my case, i could mount the card but file could not be loaded. need help...thanks....

  • #2

    Which PmmC version are you using? The latest should be fine


    • #3


      I'm using 3 uSD cards with my uLCD28. My cards are :
      - 2GB (PNY brand) -> works fine
      - 4GB (unknow brand) -> dasn't work
      - 8GB (PNY brand) -> dasn't work

      I did the same way with the 3 cards :
      - partitionned with RMPET : 1st partition FAT16, less than 2 GB
      - formatted with Win XP : FAT16, 32 KB

      So, i tried the Pmmc R32 release, an external 5V supply : no more.
      Here's the result of the uSDTester for the biggests cards :
      "media_Init sucessful - No valid MBR or partition - Table found - Sector dump : FFFFFFFFFFFFFF...."

      Somethink wrong ? Thanks for your help.


      • #4

        Is the sector dump all 0xFF? if not, try to list its full contents (Photo?)

        can you show the output of a CHKDSK against all the cards?


        • #5

          Thanks for your quick answer,

          Yes, my dump is all FF.

          - Here's CHKDSK of the 2GB (with 4 file written)

          - Here's CHKDSK of the 8GB (with no files)



          • #6

            Hmmm, reading 0xFF when windows shows a valid file system is definitely wrong.

            It may be that those cards do not support SPI mode, unfortunately there is no documented way of detecting such cards, so it's not definitive.

            We will try to get hold of some 8gb PNY cards and test them, to see what is really going on.

            Until then the best thing to do would be to avoid them.


            • #7

              I'm unluky !

              perhapse could you tell me some brands that i could be sure ?



              • #8

                SanDisk seems to be the most widely used and reliable.

                Kingston is also fairly widely used, but unforutnately as the simply rebrand cards from other manufacturers (as do a lot of brands) rather than manufacture themselves you can often have 2 cards of the same capacity that are really internally different.


                • #9

                  From the "Part_1_Physical_Layer_Simplified_Specification_Ver_3.01_Final_100518.pdf" document (available here : I read that :
                  7. SPI Mode 7.1 Introduction The SPI mode consists of a secondary communication protocol that is offered by Flash-based SD Memory Cards. This mode is a subset of the SD Memory Card protocol, designed to communicate with a SPI channel, commonly found in Motorola's (and lately a few other vendors') microcontrollers. The interface is selected during the first reset command after power up (CMD0) and cannot be changed once the part is powered on. The SPI standard defines the physical link only, and not the complete data transfer protocol. The SD Memory Card SPI implementation uses a subset of the SD Memory Card protocol and command set. The advantage of the SPI mode is the capability of using an off-the-shelf host, hence reducing the design-in effort to minimum. The disadvantage is the loss of performance of the SPI mode versus SD mode (e.g. Single data line and hardware CS signal per card). The commands and functions in SD mode defined after the Version 2.00 are not supported in SPI mode. The card may respond to the commands and functions even if the card is in SPI mode but host should not use them in SPI mode.

                  So is the SPI mode only available for Flash based SD cards? Actually are there SD cards that are not Flash based ?
                  From the last sentence it seems Version 2 SD card should not be used un SPI mode. Does that make sense ?


                  • #10

                    Another helpful reference is good old wikipedia


                    Look at the table entitled "Comparison of technical features of MMC and SD card variants"

                    According to that all Micro SD cards support SPI, but at one time, before that table existed, there was a line that read 'SPI mode support is optional for Micro SD cards'.

                    Actually, here's another reference to the Issue.

                    Every genuine 'brand name' card that we have been able to test has worked with SPI.

                    But there's a lot of brands out there that we haven't tested.

                    And just because we have tested a brand x size y card, does not mean that the manufacturer will not change 'something' that results in the next batch not working (there's a long story there, don't ask).


                    • #11

                      The trouble was coming from the PNY card. I've bought 2 new uSD cards witch works fine :
                      - 16GB 'SanDisk'
                      - 8GB 'Lexar'
                      Partionned and formated : that's ok !

                      Thanks for your help.