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SD card corruption. Bad communication?

Former Member

Hi,

 

I am having corruption occur on our SD card files and believe I am having an issue with ringing on our SD card communication lines. The corruption occurs anywhere between 2 days and 2 weeks or writing to the SD card every hour (simple logging).

 

Our current design has a PIC18F6722 connected via SPI to 3 peripherals (Flash memory, Ethernet IC and an SD card interface). In total there is at least 20cm of trace length for the SPI lines between these peripherals.  The traces also connect to other SPI peripherals, which are always disabled when we communicate with the SD card.

 

My current design does not have EMI filters or termination between the PIC and SD card. I am thinking our signal ringing, or reflections may have something to do with the fact there is no termination on the line.

 

Has anyone experienced this? Does anyone have an example schematic for interfacing a PIC with an SD card?

 

Thanks in advance for your help.

 

Cheers,

  • 0

    Hi, the SD card protocol used in many applications, is the basic SPI (one out data, one in data, one clock line). Such mode was implemented since first MMC cards, the real innovative flash memories. When you write a sector of data (512 bytes) on a card, you can verify the correctness of data, but this check is not accomplished in all the softwares. In my opinion, the wire length isn't very important, if you use a low clock frequency. I suggest to add some low value resistor on all lines, just to cancel the ringing effects of the lines, expecially on the clock line. Put a 220/330 Ohm resistor just near the processor SPI Clock line and look if the results are better. A fast speed clock, on a long line, can introduce ringing effects on fast transients. Some of these transients can be interpreted as "false clocks" from the SD card, then can corrupt writings, readings, commands, and obviously... generate errors. Hope this helps, bye