sd-dat

4. 📍 Embedded vs. Removable == SD VS SDMMC

Feature	SD Card	eMMC / SDMMC-connected storage
Removable	✅ Yes	❌ No (soldered)
Typical use	Cameras, laptops, dev boards	Phones, tablets, SBC eMMC boot
Speed	Good, but depends on class	Higher with HS200/HS400 modes
Interface	SPI or SD native	SD/MMC native only

📝 Key Points

SDMMC usually refers to the native high-speed SD/MMC bus on MCUs/SoCs.
Normal SD card can use that SDMMC bus — or just SPI mode — depending on the hardware.
In embedded boards (like STM32, ESP32-S3, Raspberry Pi), SDMMC peripheral = faster, multi-bit parallel bus.
eMMC is basically an MMC chip soldered permanently, always accessed via the SDMMC interface.

Comparison: SDIO vs. SPI Interface

Both SDIO (Secure Digital Input Output) and SPI (Serial Peripheral Interface) are used for communication with SD cards and other peripherals, but they have key differences in speed, complexity, and use cases.

Feature Comparison

Feature	SDIO Interface	SPI Interface
Bus Type	Parallel (4-bit or 1-bit)	Serial (1-bit)
Speed	Faster (up to 100+ Mbps)	Slower (typically 1–25 Mbps)
Data Lines	4-bit mode: CLK, CMD, DATA0-3 1-bit mode: CLK, CMD, DATA0	MOSI, MISO, SCK, CS (1-bit communication)
Complexity	More complex (requires SD controller)	Simpler (easier to implement in microcontrollers)
Performance	Higher data transfer rate	Lower data rate
Power Consumption	More efficient for high-speed transfers	Can be less efficient due to longer transfers
Multi-Device Support	Can support multiple devices efficiently	Requires separate chip select (CS) lines for each device
Use Cases	SD cards, Wi-Fi modules, Bluetooth modules, GPS, and high-speed peripherals	Simple microcontroller communication, low-speed SD card access, sensors, small displays

Summary

SDIO is better for high-speed data transfers (e.g., Wi-Fi, SD cards in high-performance applications).
SPI is simpler, easier to implement, and works well for low-speed, low-power applications where high transfer rates are not required.

SPI inteface for ESP32-WROVER

SP 4-wire - SPI-dat

#define SD_CS IO13
#define SD_MISO IO2
#define SD_MOSI IO15
#define SD_CLK IO14

https://github.com/Edragon/Arduino-ESP32/tree/master/Sketchbook/driver-Data

This is how I connected my SD card:

https://github.com/espressif/arduino-esp32/tree/master/libraries/SD

1-bit microSD

CMD
CLK
DATA == D0

SDIO interface for ESP32 == 4-bit mode

SD (Secure Digital) card interface, specifically the SDIO (Secure Digital Input Output) or 4-bit SD mode.

Dat 0~4 used in SCM1030-dat

MicroSD Card Connections

The following pins are used to interface with the microSD card when it is on operation.

MicroSD card	ESP32		extra
CLK	GPIO 14
CMD	GPIO 15	pull-up
DATA0	GPIO 2	pull-up
DATA1	GPIO 4	pull-up (not working)	flashlight
DATA2	GPIO 12	X
DATA3	GPIO 13	pull-up

official arduino code - SD

Note: The SPI pins can be manually configured by using SPI.begin(sck, miso, mosi, cs). Alternatively, you can change the CS pin and use the other default settings by using SD.begin(cs).

+--------------+---------+-------+----------+----------+----------+----------+----------+
| SPI Pin Name | ESP8266 | ESP32 | ESP32‑S2 | ESP32‑S3 | ESP32‑C3 | ESP32‑C6 | ESP32‑H2 |
+==============+=========+=======+==========+==========+==========+==========+==========+
| CS (SS)      | GPIO15  | GPIO5 | GPIO34   | GPIO10   | GPIO7    | GPIO18   | GPIO0    |
+--------------+---------+-------+----------+----------+----------+----------+----------+
| DI (MOSI)    | GPIO13  | GPIO23| GPIO35   | GPIO11   | GPIO6    | GPIO19   | GPIO25   |
+--------------+---------+-------+----------+----------+----------+----------+----------+
| DO (MISO)    | GPIO12  | GPIO19| GPIO37   | GPIO13   | GPIO5    | GPIO20   | GPIO11   |
+--------------+---------+-------+----------+----------+----------+----------+----------+
| SCK (SCLK)   | GPIO14  | GPIO18| GPIO36   | GPIO12   | GPIO4    | GPIO21   | GPIO10   |
+--------------+---------+-------+----------+----------+----------+----------+----------+

For more info see file README.md in this library or on URL:
https://github.com/espressif/arduino-esp32/tree/master/libraries/SD

official arduino code - SD_MMC

// Default pins for ESP-S3
// 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-WROOM-1 does not have GPIO 33 and 34 broken out.
// Note: if it's ok to use default pins, you do not need to call the setPins
int clk = 14;
int cmd = 15;
int d0 = 2;
int d1 = 4;
int d2 = 12;
int d3 = 13;  // GPIO 34 is not broken-out on ESP32-S3-DevKitC-1 v1.1

arduino code

#include <SPI.h>
#include <SD.h>
File myFile;

void setup()
{
// Open serial communications and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for Leonardo only
}
Serial.print("Initializing SD card...");
// On the Ethernet Shield, CS is pin 4. It's set as an output by default.
// Note that even if it's not used as the CS pin, the hardware SS pin
// (10 on most Arduino boards, 53 on the Mega) must be left as an output
// or the SD library functions will not work.
pinMode(10, OUTPUT);
if (!SD.begin(4)) {
Serial.println("initialization failed!");
return;
}
Serial.println("initialization done.");
// open the file. note that only one file can be open at a time,
// so you have to close this one before opening another.
myFile = SD.open("test.txt", FILE_WRITE);
// if the file opened okay, write to it:
if (myFile) {
Serial.print("Writing to test.txt...");
myFile.println("Hello,world!");
// close the file:
myFile.close();
Serial.println("done.");
} else {
// if the file didn't open, print an error:
Serial.println("error opening test.txt");
}
// re-open the file for reading:
myFile = SD.open("test.txt");
if (myFile) {
Serial.println("test.txt:");
// read from the file until there's nothing else in it:
while (myFile.available()) {
Serial.write(myFile.read());
}
// close the file:
myFile.close();
} else {
// if the file didn't open, print an error:
Serial.println("error opening test.txt");
}
}

void loop()
{
// nothing happens after setup
}