Interfacing with the MMC/SD Module
Setup and Use of the Multimedia Card/Secure Digital Host Controller Application Note, Rev. 0
Freescale Semiconductor
9
block of data then repeats.
Figure 2
is a screenshot of both the SD_CLK and the SD_DAT [0] pins
running on the i.MX1 using DMA transfer.
Figure 2. SD_CLK (1) and SD_DAT [0] (2) Multiple Block Write
4.3.2
Block Read
Blocks of data are read by sending data from the MMC/SD card to the host. Reading the data in the
MMC/SD card occurs during the data transfer mode. Commands for reading data are as follows:
•
CMD17
READ_SINGLE_BLOCK
•
CMD18
READ_MULTIPLE_BLOCK
•
CMD30
SEND_WRITE_PROT
•
CMD56
GEN_CMD
•
ACMD51 SEND_SCR
After a read command is implemented the SD_CLK starts automatically and the FIFO fills with data
from the MMC/SD card. After the FIFO is full the SD_CLK stops. During this point the data from the
FIFO automatically is loaded into memory (RAM). When all the data has been loaded into memory the
SD_CLK starts again to get the next block of data from the MMC/SD card.
Figure 3
is a screenshot of
both the SD_CLK and SD_DAT [0] pins of the i.MX1 using DMA transfer.