arduino-esp32/libraries/SD_MMC

SD_MMC library

This library provides the integration of ESP32 and ESP32-S3 with SD (Secure Digital) and MMC (Multi Media Card) cards using a built-in SDMMC module.

Please note that SD_MMC is only available for ESP32 and ESP32-S3. For other SoCs please use the SD library based on SPI.

Wiring:

Image source: Wikipedia

Image source: Wikipedia

pin number (refer to the picture)	micro SD - SD mode	micro SD - SPI mode	mini SD - SD mode	mini SD - SPI mode	SD - SD mode	SD - SPI mode	MMC (MMC3) - MMC mode	MMC (MMC3) - SPI mode	MMCplus / MMCmobile (MMC4) - MMC mode	MMCplus / MMCmobile (MMC4) - SPI mode
1	D2	not used	D3	CS	D3	CS	RES	CS	D3	CS
2	D3	CS	CMD	DI	CMD	DI	CMD	DI	CMD	DI
3	CMD	DI	VSS1 (GND)	VSS1 (GND)	VSS1 (GND)	VSS1 (GND)	VSS1 (GND)	VSS1 (GND)	VSS1 (GND)	VSS1 (GND)
4	VDD (3.3V)	VDD (3.3V)	VDD (3.3V)	VDD (3.3V)	VDD (3.3V)	VDD (3.3V)	VDD (3.3V)	VDD (3.3V)	VDD (3.3V)	VDD (3.3V)
5	CLK	SCLK	CLK	SCLK	CLK	SCLK	CLK	SCLK	CLK	SCLK
6	VSS (GND)	VSS (GND)	VSS2 (GND)	VSS2 (GND)	VSS2 (GND)	VSS2 (GND)	VSS2 (GND)	VSS2 (GND)	VSS2 (GND)	VSS2 (GND)
7	D0	DO	D0	DO	D0	DO	DAT	DO	D0	DO
8	D1	not used	D1	not used	D1	not used	-	-	D1	not used
9	-	-	D2	not used	D2	not used	-	-	D2	not used
10	-	-	For future use	For future use	-	-	-	-	D3	not used
11	-	-	For future use	For future use	-	-	-	-	D4	not used
12	-	-	-	-	-	-	-	-	D5	not used
13	-	-	-	-	-	-	-	-	D6	not used

Pin assignments for ESP32

On ESP32, SD_MMC peripheral is connected to specific GPIO pins and cannot be changed (rerouted). Please see the table below for the pin connections.

When using an ESP-WROVER-KIT board, this example runs without any extra modifications required. Only an SD card needs to be inserted into the slot.

ESP32 pin	SD card pin	Notes
GPIO14 (MTMS)	CLK	10k pullup in SD mode
GPIO15 (MTDO)	CMD	10k pullup in SD mode
GPIO2	D0	10k pullup in SD mode, pull low to go into download mode (see Note about GPIO2 below!)
GPIO4	D1	not used in 1-line SD mode; 10k pullup in 4-line SD mode
GPIO12 (MTDI)	D2	not used in 1-line SD mode; 10k pullup in 4-line SD mode (see Note about GPIO12 below!)
GPIO13 (MTCK)	D3	not used in 1-line SD mode, but card's D3 pin must have a 10k pullup

Pin assignments for ESP32-S3

On ESP32-S3, SDMMC peripheral is connected to GPIO pins using GPIO matrix. This allows arbitrary GPIOs to be used to connect an SD card or MMC. The GPIOs can be configured with the following commands:

  setPins(int clk, int cmd, int d0))
  setPins(int clk, int cmd, int d0, int d1, int d2, int d3))

The table below lists the default pin assignments.

When using an ESP32-S3-USB-OTG board, this example runs without any extra modifications required. Only an SD card needs to be inserted into the slot.

ESP32-S3 pin	SD card pin	Notes
GPIO36	CLK	10k pullup
GPIO35	CMD	10k pullup
GPIO37	D0	10k pullup
GPIO38	D1	not used in 1-line SD mode; 10k pullup in 4-line mode
GPIO33	D2	not used in 1-line SD mode; 10k pullup in 4-line mode
GPIO34	D3	not used in 1-line SD mode, but card's D3 pin must have a 10k pullup

Warning: ESP32-S3-WROOM-2 is using most of the default GPIOs (33-37) to interface with on-board OPI flash. If the SD_MMC is initialized with default pins it will result in rebooting loop - please reassign the pins elsewhere using the mentioned command setPins.

Note: ESP32-S3-DevKitC-1 v1.1 does NOT have GPIOs 33 and 34 broken out, so it will be necessary to change at least the pin for D2 and D3.

4-line and 1-line SD modes

By default, this library uses 4-bit line mode, utilizing 6 pins: CLK, CMD, D0 - D3 and 2 power lines (3.3V and GND). It is possible to use 1-bit line mode (CLK, CMD, D0, 3.3V, GND) by passing the second argument mode1bit==true:

  SD_MMC.begin("/sdcard", true);

Note: Even if card's D3 line is not connected to the ESP chip, it still has to be pulled up, otherwise the card will go into SPI protocol mode.

Note about GPIO2 (ESP32 only)

GPIO2 pin is used as a bootstrapping pin, and should be low to enter UART download mode. One way to do this is to connect GPIO0 and GPIO2 using a jumper, and then the auto-reset circuit on most development boards will pull GPIO2 low along with GPIO0, when entering download mode.

• Some boards have pulldown and/or LED on GPIO2. LED is usually ok, but pulldown will interfere with D0 signals and must be removed. Check the schematic of your development board for anything connected to GPIO2.

Note about GPIO12 (ESP32 only)

GPIO12 is used as a bootstrapping pin to select output voltage of an internal regulator which powers the flash chip (VDD_SDIO). This pin has an internal pulldown so if left unconnected it will read low at reset (selecting default 3.3V operation). When adding a pullup to this pin for SD card operation, consider the following:

FAQ:

Do I need any additional modules, like the Arduino SD module?

No, just wire your SD card directly to ESP32.

Tip: If you are using a microSD card and have a spare adapter to full-sized SD, you can solder Dupont pins on the adapter.

What is the difference between SD and SD_MMC libraries?

SD runs on SPI, and SD_MMC uses the SDMMC hardware bus on the ESP32. The SPI uses 4 communication pins + 2 power connections and operates on up to 80 MHz. The SPI option offers flexibility on pin connection because the data connections can be routed through GPIO matrix to any data pin. SD-SPI speed is approximately half of the SD-MMC even when used on 1-bit line. You can read more about SD SPI in the documentation

SD_MMC is supported only by ESP32 and ESP32-S3 and can be connected only to dedicated pins. SD_MMC allows to use of 1, 4 or 8 data pins + 2 additional communication pins and 2 power pins. The data pins need to be pulled up externally. You can read more about SD_MMC in the documentation 1-bit: SD_MMC_ speed is approximately two-times faster than SPI mode 4-bit: SD_MMC speed is approximately three-times faster than SPI mode.