Texas Instruments TMS320DM644x manual Clock Control, MMC/SD Controller Clocking Diagram

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Peripheral Architecture

2.1Clock Control

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 clock to the MMC/SD card(s). The MMC/SD controller is capable of operating with a function clock up to 100 MHz.

The memory clock appears on the SD_CLK pin of the MMC/SD controller interface. The memory clock controls 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-down value is set by CLKRT bits in the MMC memory clock control register (MMCCLK) and is determined by the following equation:

memory clock frequency = function clock frequency/(2 × (CLKRT + 1))

MMC/SD input clock

Figure 4. MMC/SD Controller Clocking Diagram

MMC/SD controller

MMCCLK (CLKRT)

Memory clock

on CLK pin

Function clock for

MMC/SD controller

MMC/SD

card

(1)Maximum memory clock frequency in MMC card can be 20 MHz.

(2)Maximum memory clock frequency in SD card can be 50 MHz.

12 Multimedia Card (MMC)/Secure Digital (SD) Card Controller SPRUE30B –September 2006

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