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nrf51 (spim) <-> sd card

Stanislav Silnitskiy

Hello! Do I need any extra passives, connecting SD card to SPIM of nRF51? It works fine with MOSI, MISO, SCK, SEL, VCC and GND directly connected, just want to be sure it will not surprise me one day.

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    From reading various sources on the internet it seems that you should use pull-up resistors on all logic lines, or else some SD cards may not work. This is because the lines are floating when the SD card is not inserted or when the nRF chip boots up. Using pull-up on all pins seems to be a part of the SD card spec (have not confirmed this).

    Adding pull-up resistors in the layout will not do any harm since you can choose to leave them unconnected. They will take up space however.

  • 0 in reply to Ole Bauck

    Hi Ole, Thank you guiding me! But what the problem is, when nRF is booting? As to my knowledge, it starts from some address of code, found in nrf51x_____.S, then, if SoftDev is used, it passes control to softedev and then to my app, where I configure pins with internal pull-ups. So, from the SD card's point of view, it receives power, then some time pins are floating, then pins are pulled-up and after all card receives first commands from my app. If this scenario is correct, where it can fail or lead to following fails?

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  • 0 in reply to Ole Bauck

    Hi Ole, Thank you guiding me! But what the problem is, when nRF is booting? As to my knowledge, it starts from some address of code, found in nrf51x_____.S, then, if SoftDev is used, it passes control to softedev and then to my app, where I configure pins with internal pull-ups. So, from the SD card's point of view, it receives power, then some time pins are floating, then pins are pulled-up and after all card receives first commands from my app. If this scenario is correct, where it can fail or lead to following fails?

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