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sdcardio: Configure internal pull-up on MISO #8941

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rgov opened this issue Feb 17, 2024 · 6 comments
Open

sdcardio: Configure internal pull-up on MISO #8941

rgov opened this issue Feb 17, 2024 · 6 comments
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@rgov
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rgov commented Feb 17, 2024

According to this page, when communicating with an SD card in SPI mode,

A pull-up on the DO (MISO) cannot be omited, or some cards will fail initialization process.

There exists common_hal_digitalio_digitalinout_set_pull() which can configure internal pull-ups on some MCUs. Is this something sdcardio could do for us?

@tannewt tannewt added this to the Long term milestone Feb 20, 2024
@tannewt
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tannewt commented Feb 20, 2024

Right now busio.SPI() doesn't allow it. What value do they suggest for Rpu?

@rgov
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rgov commented Feb 20, 2024

I'm not sure. Adafruit's breakout board uses a 47kΩ resistor. Espressif has some documentation that suggests a 10k resistor.

@dhalbert
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I don't see that pullup in this older breakout: https://learn.adafruit.com/adafruit-micro-sd-breakout-board-card-tutorial/download, or on, say the Feather M0 Datalogger. These boards do work, hmm.

@ladyada Have you heard about this desired pullup on MISO on SD cards?

@ladyada
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ladyada commented Feb 21, 2024

never heard of it before. traditionally we only need a pullup on the CS line. however, we should initialize the SD card first!

@tannewt
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tannewt commented Feb 21, 2024

The page states According to SDC/MMC specs, from 50k to 100k ohms is recommended to the value of pull-up registers.

My gut is that this should be the board's job. Not a use for internal pulls.

@dhalbert
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dhalbert commented Feb 1, 2025

Could be done via #9845.

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