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Micro SD and card detect


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I'm working with a 3M microSD card holder (mainly because the footprint already exists in the AdaFruit libraries)....but I'm having some issues making sense out of it.  The footprint is setup with the two tabs on the back labeled as "card detect".  However, these tabs just connect to the metal case, which then connect directly to ground elsewhere.  So as it sits, the card detect line is just a direct connection to ground.

 

I pulled the data sheet and the only piece of info it has is a cryptic diagram saying when the card is in, pin #2 is connected to pad #2 (card).  So when the card is in, pad #2 makes contact with pin #2 on the sd card?  No kidding...never would have thought that.  Next you'll tell me pin 1 gets connected to pad 1.  I did pull one of the cases apart and verified that there is no physical switch inside the case that connects any pad to anything else when the card is inserted.  Also, pin 2 is the chip select line...so I'm failing to see how it can function as both chip select and card detect.

 

Any ideas....or maybe a better part that isn't so weird?

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#CD should be a NC contact switch that is opened whenever a card is inserted.

Your socket could create a short between the #CD pin and ground through an SD pin; two contacts that contact the same pad and thus create a conducting path.

This sounds ugly, the card detect should function through a separate line, not affecting the SD protocol.

Apparently pad 2 of the SD card is the card detect pin. That is, it is when in SD 1bit or 4 bit mode. When in SPI mode the pin becomes the chip select.

So as long as you're in SD mode you can probe pin 2 for card presence, but when you switch to SPI mode you lose this function.

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