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Topic: SPI SD card reader & other SPI device not working together (Read 729 times) previous topic - next topic

Ray_Beebe

Spent sevral hours trying to figure out the odd behavior of an micro SD card reader with an SPI camera module. Both worked fine on their own, but when used together either SPI camera or Card failure occurred almost all the time.

Turns out the SD card readers improper design was the problem.  A quick look at the card reader shows an LVC125A Tri-state buffer is used for CS, MOSI, MISO and SCK. Looked good, but after checking all connections it turns out all the OE's for the LVC125 are active all the time. The CS pin went into the buffer and out to the SD card only. The Tri-sate capability of the chip was not being use! That would work for CS, MOSI and SCK but not for  MISO - an output. The MISO buffer output was always driving the SPI bus high or low even when other SPI devices were active. Totally unbelievable a tri-state buffer is used in a design and its tri-state capability not used at all!

The solution was to unsolder buffer pin 13 from the board then solder a wire between pin 13 and the CS input. Then use some hot glue to protect the hair thin wire and solder work. Now when the SD cards CS is high or low the MISO output is high impedance or active.

I've been writing and reading images to the micro SD card with no issues at all now.

issraar

Hello @Ray_Beebe,

could you please let me know which one is CS Input , pin 8 or 9 ??

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