Texas Instruments TMS320DM644x User Manual
www.ti.com
2.8
Reset Considerations
2.8.1
Software Reset Considerations
2.8.2
Hardware Reset Considerations
2.9
Initialization
2.9.1
MMC/SD Controller Initialization
2.9.2
Initializing the MMC Control Register (MMCCTL)
Peripheral Architecture
The MMC/SD peripheral has two reset sources: hardware reset and software reset.
A software reset (such as a reset that the emulator generates) does not cause the MMC/SD controller
registers to alter. After a software reset, the MMC/SD controller continues to operate as it was configured
prior to the reset.
registers to alter. After a software reset, the MMC/SD controller continues to operate as it was configured
prior to the reset.
A hardware reset of the processor causes the MMC/SD controller registers to return to their default values
after reset.
after reset.
The general procedure for initializing the MMC/SD controller is given in the following steps. Details about
the registers or register bit fields to be configured in the MMC/SD mode are in the subsequent
subsections.
the registers or register bit fields to be configured in the MMC/SD mode are in the subsequent
subsections.
1. Place the MMC/SD controller in its reset state by setting the CMDRST bit and DATRST bit in the MMC
control register (MMCCTL). You can set other bits in MMCCTL after reset.
2. Write the required values to other registers to complete the MMC/SD controller configuration.
3. Clear the CMDRST bit and the DATRST bit in MMCCTL to release the MMC/SD controller from its
3. Clear the CMDRST bit and the DATRST bit in MMCCTL to release the MMC/SD controller from its
reset state. It is recommended not to rewrite the values that are written to the other bits of MMCCTL in
.
4. Enable the SD_CLK pin so that the memory clock is sent to the memory card by setting the CLKEN bit
in the MMC memory clock control register (MMCCLK).
Note:
The MMC/SD cards require a clock frequency of 400 kHz or less for the card initialization
procedure. Make sure that the memory clock confirms this requirement. Once card
initialization completes, you can adjust the memory clock up to the lower of the card
capabilities or the maximum frequency that is supported.
procedure. Make sure that the memory clock confirms this requirement. Once card
initialization completes, you can adjust the memory clock up to the lower of the card
capabilities or the maximum frequency that is supported.
The bits in the MMC control register (MMCCTL) affect the operation of the MMC/SD controller. The
subsections that follow help you decide how to initialize each of control register bits.
subsections that follow help you decide how to initialize each of control register bits.
In the MMC/SD mode, the MMC/SD controller must know how wide the data bus must be for the memory
card that is connected. If an MMC card is connected, specify a 1-bit data bus (WIDTH = 0 in MMCCTL); if
an SD card is connected, specify a 4-bit data bus (WIDTH = 1 in MMCCTL).
card that is connected. If an MMC card is connected, specify a 1-bit data bus (WIDTH = 0 in MMCCTL); if
an SD card is connected, specify a 4-bit data bus (WIDTH = 1 in MMCCTL).
To place the MMC/SD controller in its reset state and disable it, set the CMDRST bit and DATRST bit in
MMCCTL. The first step of the MMC/SD controller initialization process is to disable both sets of logic.
When initialization is complete, but before you enable the SD_CLK pin, clear the CMDRST bit and
DATRST bit in MMCCTL to enable the MMC/SD controller.
MMCCTL. The first step of the MMC/SD controller initialization process is to disable both sets of logic.
When initialization is complete, but before you enable the SD_CLK pin, clear the CMDRST bit and
DATRST bit in MMCCTL to enable the MMC/SD controller.
SPRUE30B – September 2006
Multimedia Card (MMC)/Secure Digital (SD) Card Controller
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