Intel PXA255 manual Signal Description, MMC Controller Reset, Card Initialization Sequence

MultiMediaCard Controller

15.2.1Signal Description

The MMC controller signals are MMCLK, MMCMD, MMDAT, MMCCS0, and MMCCS1. Table 15-4describes each signal’s function.

Table 15-4. MMC Signal Description

Signal Name	Input/Output	Description
MMCLK	Output	Clock signal to MMC
MMCMD	BiDirectional	Command line
MMDAT	BiDirectional	Data line
MMCCS0	Output	Chip Select 0 (used only in SPI mode)
MMCCS1	Output	Chip Select 1 (used only in SPI mode)

The MMCLK, MMCCS0, and MMCCS1 signals are routed through alternate functions within the GPIO. Refer to Section 4.1, “General-Purpose I/O” on page 4-1for a description of the process 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 Section 4.1.2, “GPIO Alternate Functions” on page 4-2for a complete description of the GPIO alternate functions.

15.2.2MMC 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 Section 2.6, “Reset” on page 2-6. All registers and FIFO controls are set to their default values after any reset.

15.2.3Card 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 15-18for command definitions) by loading the appropriate command index into the 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.

15.2.4MMC 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 Intel® PXA255 Processor Developer’s Manual