Intel PXA27 Series Design Manual page 169

Table 15-3. MMC/SD/SDIO Controller Supported Device Configurations
Controller
Mode
MMC/SD/SDIO
SPI
The PXA27x processor MMC/SD/SDIO card controller communicates at a maximum data rate of
19.5 Mbps for MMC, 1-bit SD/SDIO, and SPI mode data transfers. The maximum data rate is
78 Mbps for 4-bit SD/SDIO data transfers.
The 3.3 V regulator serves several purposes in the reference platform:
•
Provides a clean 3.3 V supply to the MMC/SD/SDIO Card socket.
•
Serves to protect the main voltage supply on the board from being shorted or damaged by a
defective MMC/SD/SDIO Card device; there is the possibility of the MMC/SD/SDIO voltage
regulator being damaged instead.
•
Provides ability to easily power down the MMC/SD/SDIO Card socket without having to
power down the main 3.3 V supply.
The system designer determines whether to implement a dedicated regulator or pass-transistor for
supplying 3.3 V to the MMC/SD/SDIO socket. The decision is based upon analysis of functionality
versus component/board real estate costs.
®
Intel PXA27x Processor Family Design Guide
Comm
Maximum Devices Supported
Protocol
MMC MMC device stack size
determined by signal loading
limitations
SD One SD Card
SDIO One SDIO Card
SPI Two SD Cards, SDIO Cards,
two MMC Devices, or a
combination of two device types
MultiMediaCard/SD/SDIO Card Controller
Description
MMC protocol supports multiple cards.
Each SD Card must have its own data bus.
The PXA27x processor MMC/SD/SDIO
controller supports one data bus.
Each SDIO Card must have its own data bus.
The PXA27x processor MMC/SD/SDIO
controller supports one data bus.
MMC/SD/SDIO controller of the PXA27x
processor supports these devices:
•
2 chip selects
•
MMCCS<0>
•
MMCCS<1 >
The specified devices must be in SPI mode.
II:15-3