sd card problem / GPIO drive

[Michal]

Hello,

I have a problem with communicating with SD cards (https://devzone.nordicsemi.com/f/nordic-q-a/34401/fatfs-example-does-not-work-with-every-sd-card). I resloved partially my problems with configuring SCK and MOSI lines to H0H1. But I still have problems with some of SD cards. Is it possible that nrf gpios drive is not "strong" enough to properly control SPI lines? Or may it be that current peak caused by SD card have introduced some noise to power lines and to SPI lines?

I tried resolving this problem at software level but no configuration is helping.

I am testing on standard fatfs example from sdk 15.2.

Regards,

Michał

[haakonsh]

I'd try to lower the CLK speed incrementally and see if that helps. I would also scope the IO lines with both a digital analyzer and a regular oscilloscope to see if there's something out of place. 

[Michal]

Thanks, I tried it all. I lowered CLK speed to lowest and did not get better results. Also I was checking lines with logic analyzer and I saw that sometimes lines go high or low for microseconds when they should not.

I am wondering if because of too weak drive of gpios nrf may not be able to drive some of SD cards over SPI?

[haakonsh]

"I am wondering if because of too weak drive of gpios nrf may not be able to drive some of SD cards over SPI?"
One way to test that hypothesis is to drive the I/O lines by external MOSFETs. 

"Or may it be that current peak caused by SD card have introduced some noise to power lines and to SPI lines?"
Try decoupling the SD card supply with 4,7µF in parallell with 100nF, and 1nF.