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SD card - pull-ups required?

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gmorfeus

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Hi,

I am designing a PCB that will have micro sd card glued into sd card slot so there will be no chance of removing it (or disconnecting) from microcontroller. In such configuration, are pull-up resistors needed? As I understand, pull-ups are required on all pins except CLK and D3 pin?
Thanks.

Gabrijel
 

Hi,

I'm sure there are standard circuits for SD connections.

Did you do an internet search?

Klaus
 

I am designing a PCB that will have micro sd card glued into sd card slot so there will be no chance of removing it (or disconnecting) from microcontroller.
I'm not so sure that this is a good idea as SD cards have a limited write/erase cycle life. Depending on how you intend to use the SD card, this could mean that the whole device needs to be replaced if any part of the SD card fails.
Perhaps make the device enclosed in a box such that you need to open the box to access the SD card so that it can at least be replaced (even if not 'easily').
Susan
 

The pull-up resistors are for protecting the CMD and the DAT lines against bus floating when no card is inserted. So if the SD card is permanetly fitted, pull-up resistors are not needed.
 

Well, sd card will be used just for write and once the data is written, it won't be erased or overwritten. So there is no problem that it will die because of write/erase cycle.
I've found circuits how to connect sd card, but looked to me that pull-up resistors are used to be sure that lines are not floating while there is no sd card. I have also find (don't remember where exactly) that they are used to have definite line state while processor is booting. I find that strange while usually booting processor put all pins in hi-z while booting and that shouldn't be a problem for sd card. Did anyone tried connecting sd card without any pull-up resistors and all was working ok?
 

I have used an SD card without any pull ups. But depending on the micro used this may cause extra current to be drawn when no SD card is present. If in single bit mode (SPI) the three unused SD card inputs should have pull up resistors, although I have found that they make no practical difference but may reduce current. Note that pull up resistors connected to a SD card output must be greater than 50Kohm.
 

@pjmelect: Thanks a lot! That are all excellent information. I think that I'll just go with "proposed design": with pull-up resistors regardless if the sd card won't be possible to remove.

Thank you all for your help.

Gabrijel
 

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