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.

[Ole Bauck]

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.

[Stanislav Silnitskiy]

I'm a newby in embedded systems, so stupid question:

nrf51_bitfields.h:

#define GPIO_PIN_CNF_PULL_Pullup (0x03UL) /*!< Pullup on pin. */

using it when configuring SPIM pins makes a work, or just notifies nRF51 hardware, that there is a passive on the line, which pulls the line up?