Signal Description; Mmc Controller Reset; Card Initialization Sequence; Mmc And Spi Modes - Intel PXA255 Developer's Manual

MultiMediaCard Controller
15.2.1

Signal Description

The MMC controller signals are MMCLK, MMCMD, MMDAT, MMCCS0, and MMCCS1.
Table 15-4
Table 15-4. MMC Signal Description
Signal Name
MMCLK
MMCMD
MMDAT
MMCCS0
MMCCS1
The MMCLK, MMCCS0, and MMCCS1 signals are routed through alternate functions within the
GPIO. Refer to
used to assign these signals to a specific GPIO. Even though there are several GPIO assigned to
each signal, each signal must be programmed to one of the possible GPIOs. Refer to
"GPIO Alternate Functions" on page 4-2
functions.
15.2.2

MMC Controller Reset

The MMC controller can only be reset by a hard or soft reset of the processor. The ways to reset the
processor and the MMC controller can be found in
and FIFO controls are set to their default values after any reset.
15.2.3

Card Initialization Sequence

After reset, the MMC card must be initialized by sending 80 clocks to it on the MMCLK signal. To
initialize the MMC card, set the MMC_CMDAT[INIT] bit to a 1. This sends 80 clocks before the
current command in the MMC_CMD register. This function is useful for acquiring new cards that
have been inserted on the bus. Chip selects are not asserted during the initialization sequence.
After the 80-clock initialization sequence, the software must continuously send CMD1 (see
Table 15-18
MMC_CMD register until the card indicates that the power-up sequence is complete. The software
can then assign an address to the card or put it into SPI mode.
15.2.4

MMC and SPI Modes

After reset, the MMC card is in the MMC mode. The card may remain in MMC mode or be
configured to SPI mode by setting the MMC_SPI register bits. The following sections briefly
describe each mode as it pertains to the MMC controller.
15-6
describes each signal's function.
Input/Output
Output Clock signal to MMC
BiDirectional Command line
BiDirectional Data line
Output Chip Select 0 (used only in SPI mode)
Output Chip Select 1 (used only in SPI mode)
Section 4.1, "General-Purpose I/O" on page 4-1
for command definitions) by loading the appropriate command index into the
Description
for a description of the process
for a complete description of the GPIO alternate
Section 2.6, "Reset" on page
Intel® PXA255 Processor Developer's Manual
Section 4.1.2,
2-6. All registers