SD Pull-up Requirements

[中文]

Espressif hardware products are designed for multiple use cases which may require different pull states on pins. For this reason, the pull state of particular pins on certain products needs to be adjusted to provide the pull-ups required in the SD bus.

SD pull-up requirements apply to cases where ESP32-S3 uses the SPI or SDMMC controller to communicate with SD cards. When an SD card is operating in SPI mode or 1-bit SD mode, the CMD and DATA (DAT0 - DAT3) lines of the SD bus must be pulled up by 10 kΩ resistors. SD cards and SDIO devices should also have pull-ups on all above-mentioned lines (regardless of whether these lines are connected to the host) in order to prevent them from entering a wrong state.

This document has the following structure:

• Overview of Compatibility between the default pull states on pins of Espressif's products and the states required by the SD bus

• Solutions - ideas on how to resolve compatibility issues

• Related Information - other relevant information

Overview of Compatibility

This section provides an overview of compatibility issues that might occur when using SDIO (secure digital input output). Since the SD bus needs to be connected to pull-ups, these issues should be resolved regardless of whether they are related to master (host) or slave (device). Each issue has links to its respective solution. A solution for a host and device may differ.

Systems on a Chip (SoCs)

ESP32-S3 SDMMC host controller allows using any of GPIOs for any of SD interface signals. However, it is recommended to avoid using strapping GPIOs, GPIOs with internal weak pull-downs and GPIOs commonly used for other purposes to prevent conflicts.

• GPIO0 (strapping pin)

• GPIO45, GPIO46 (strapping pins, internal weak pulldown)

• GPIO26 - GPIO32 (commonly used for SPI flash and PSRAM)

• GPIO33 - GPIO37 (when using chips and modules with octal SPI flash or octal PSRAM)

• GPIO43, GPIO44 (GPIOs used for UART0 by default)

• GPIO19, GPIO20 (GPIOs used for USB by default)

Development Boards

• ESP32-S3-DevKitC-1

  • No Pull-ups

• ESP32-S3-USB-OTG

  • The board may be used in 1-line and 4-line SD mode or SPI mode.

  • Required pull-ups are provided on GPIOs 33-38.

• ESP32-S3-EYE

  • The board is limited to 1-line SD mode.

  • Required pull-ups are provided on GPIOs 38-40.

Solutions

No Pull-ups

When using a development board without pull-ups:

• If your host and slave device are on separate boards, replace one of them with a board that has pull-ups. For the list of Espressif's development boards with pull-ups, go to Development Boards.

• Attach external pull-ups by connecting each pin which requires a pull-up to VDD via a 10 kΩ resistor.

Related Information

Internal Pull-ups and Strapping Requirements

Using external resistors is always preferable. However, Espressif's products have internal weak pull-up and pull-down resistors which can be enabled and used instead of external ones. Please keep in mind that this solution can not guarantee reliable SDIO communication.

Generally it's not recommended to reuse strapping pins for SDIO purposes. The pullup and pulldown requirements of SD and strapping may conflict with each other. See datasheet for the strapping pins of {IDF_TARGET}.

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