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nrf51 (spim) <-> sd card

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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0 Ole Bauck over 9 years ago

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.
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0 Ole Bauck over 9 years ago

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.
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0 Stanislav Silnitskiy over 9 years ago in reply to Ole Bauck
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?
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0 Ole Bauck over 9 years ago in reply to Ole Bauck

You can configure the pins to use internal pull up, but this will not remove the problem when the nRF boots up.
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0 Stanislav Silnitskiy over 9 years ago 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 Ole Bauck over 9 years ago in reply to Ole Bauck

"then some time pins are floating". That can cause problems, putting the SD card in some state. I have not experienced this myself, but searding on "SD SPI pull up" on the internet gave a lot of discussion on whether or not pull up was necessary. You will probably get away with no external pull up resistors.
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0 Stanislav Silnitskiy over 9 years ago in reply to Ole Bauck

Thank you, Ole, I think to put some on-board if space will allow it. It worth to have this kind of protection.
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