SD Card compatibility issues

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Source text: SD card compatibility issues

Recently encountered an issue with SD card compatibility. The main chip SD card group signal, after the adapter board, long line, and then to the SD clip board. There is a problem with multiple card compatibility.   For example, SanDisk or Samsung's OK, and Kingston's card individual capacity of the No, etc. (it is said that Kingston's card is more fakes on the market).     The load characteristics of each SD card will vary. have done the related treatment, share to everybody.
The most important reason is the instability of the SD_CLK signal, the distortion is more severe. Measured waveform:

qq20150714100005.png (269.58 KB, download number: 0)

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After the circuit correction waveform is as follows:

qq20150714100026.png (191.15 KB, download number: 0)

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After the correction, at least in the low level interval, there is no previous rebound (bounce will cause chip recognition level logic error)
The overall connection, and the circuit matching parameters are as follows:

qq20150714100256.png (12.41 KB, download number: 0)

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The SD_CLK signal is added to the power board by adding a 33R string resistor and 33p ground capacitance to match (absorb signal emission and slow signal rise time, add RC terminal match (absorb transmit and echo) on SD card board.　　The RC parameter is obtained based on the actual verification of the line connection. The actual verification effect is good. has shown good compatibility with various SDKs.

SD card compatibility issues (RPM)