MMC HAT for the Raspberry Pi

The MMC HAT adds a second micro SD socket to your Raspberry Pi using the second SDIO interface.

The MMC HAT has many uses including:

• Micro SD card reader. Write new images, repair or modify existing Raspberry Pi installations with ease
• Additional storage, mount as your home directory, for general storage or backups
• RAID1 on the root (/) partition for added reliability
• Connector for USB Serial Adaptor (FTDI 3.3v)

Compatibility

OS: Only compatible with Raspberry Pi OS.

Can be used on Raspberry Pi A+, B+, Zero (with headers), Zero W* (with headers) , 2B, 3B*, 3B+* and 4B**

• * When used on a Raspberry Pi Zero W, 3B or 3B+ the on-board WiFi is disabled as it is on the SDIO interface used by the MMC HAT
• **The Raspberry Pi 4 has three SD controllers so you can use onboard SD, WiFi and the MMC HAT (SD) at the same time
• **The SD clock speed will be slower on a Pi4 when compared to the Pi4's onboard SD controller. Earlier boards (3B+ and before) will benefit from faster speed from the MMC HAT.

When using a Raspberry Pi 4 please add the following three lines to the TOP of the config.txt file in the boot directory.

[pi4]

dtparam=mmchat_pi4

[all]

Speed

With the standard SD clock speed a micro SD card in the MMC HAT (/dev/mmcblk2) performs at similar speeds to the onboard micro SD card (/dev/mmcblk0) on boards up to the 3B+.

The clock speed will be slower on a Pi4 when compared to the Pi4's onboard SD controller, as the Pi4 moved to emmc2 which improves on the original sdhost and arasan interfaces. Still, the MMC HAT is great for the Pi4 as a card reader, spare storage and the other features of this board.

Package Contents

The standard MMC HAT package contains:

• 1x MMC HAT PCB with pre-soldered header
• 4x 12mm M2.5 standoff
• 8x 6mm M2.5 screw
• 4x stick on feet