I have seen people pulling up only the CS pin, so that when the microcontroller's pins are floating in the power-up, the microSD card is not corrupted.
Also, I have seen many people pulling up and down DI,DO and SCLK lines.
Some of the circuits that I've seen even connect pins 1 and 2 to Vdd/2 via a voltage divider that is formed between Vdd and Vss.
Which pins of the microSD card should be pulled up or high when interfacing a microcontroller with an embedded SPI interface and has the appropriate logic voltage levels?
Best Answer
The specification only makes mention of the 50K\$\Omega\$ pull-up internal to the card used for card detection. It talks about this in reference to the commands used to disable it. Search for "pull" to see all the mentions of it.
However, the SanDisk SD Card Product Manual is much more helpful. From Chapter 3:
So you need to add pull-ups to all unused pins to prevent high-current from occurring due to the inputs being floating.
For the SPI signals that you will be using, pull-ups are not required. However if your traces are long or running through a noisy section on your board, or if you are running a high clock rate, adding pull-up resistors will help to clean up your signals transitions.