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2.1 Clock Control
MMCCLK
(CLKRT)
Function clock for
MMC/SD controller
MMC/SD controller
MMC/SD
input clock card
MMC/SD
Memory clock
on CLK pin
Peripheral Architecture
There are two clocks, the function clock and the memory clock, in the MMC/SD controller (Figure 4 ).
The function clock determines the operational frequency of the MMC/SD controller and is the input clockto the MMC/SD card(s). The MMC/SD controller is capable of operating with a function clock up to100 MHz.
The memory clock appears on the SD_CLK pin of the MMC/SD controller interface. The memory clockcontrols the timing of communication between the MMC/SD controller and the connected memory card.The memory clock is generated by dividing the function clock in the MMC/SD controller. The divide-downvalue is set by CLKRT bits in the MMC memory clock control register (MMCCLK) and is determined by thefollowing equation:
memory clock frequency = function clock frequency/(2 × (CLKRT + 1))
Figure 4. MMC/SD Controller Clocking Diagram
(1) Maximum memory clock frequency in MMC card can be 20 MHz.
(2) Maximum memory clock frequency in SD card can be 50 MHz.
Multimedia Card (MMC)/Secure Digital (SD) Card Controller12 SPRUE30B – September 2006Submit Documentation Feedback