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OMAPL138 SD/SDIO query

Mukul Bhatnagar
Guru* 83935 points
Other Parts Discussed in Thread: OMAPL138, CSD

Question from Customer

A SD Card can be running in Default mode or High-Speed mode for the bus timing (according to the PHYSICAL LAYER SPECIFICATION Version 1.10).

How is the switching between these modes being handled in OMAPL138? I have not found any registers controlling this.”

  • 0
    TI__Guru* 83935 points

    Response:

    To change the card transfer rate between normal (less than 20MHz) and high-speed mode (for MMC/SD controller meeting ver. 4.0 of the spec), I see  sequence recommended (via generic web search) to maintain compatibility with older controllers:

     Bus Width setting (Using by CMD6) Bus test (using by CMD14 & CMD19)

    HS_TIMING setting (using by CMD6) Change the frequency (over the 26MHz)

    Read the Extended CSD (using by CMD8)

     

    On the OMAPL138 , the bus clock/rate can be modified by changing the divide down field CLKRT of the MMCCLK register. Table 27-7 in SPRUH77A

     

  • 0 in reply to Mukul Bhatnagar
    TI__Guru** 116100 points

    Thanks Mukul for sharing the questions with answers.