65.13 e.MMC HS400 Timing Mode Selection

The HS400 mode has the following features:

• DDR data sampling method
• SDCLK frequency up to 200 MHz, Data rate is up to 400MB/s
• Only 8-bit bus width supported
• Signaling levels of 1.8V and 1.2V
• Data strobe signal is toggled only for data read, CRC response and CMD response (if Enhanced Strobe mode is supported)

HS400 mode is not supported during Boot Operation mode.

After the host driver initializes the device, it checks whether the device supports the HS400 mode by reading the field DEVICE_TYPE in the Extended CSD register of the e.MMC device (see “Embedded MultiMedia Card (e.MMC) Electrical Standard 5.01”). Then it enables the HS400 mode in the device before changing the clock frequency to a frequency higher than 52 MHz.