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DRA829V: MMC1_SDCD Pull down Notation

Mari Tsunoda
Expert 5726 points
Part Number: DRA829V

Hi Team,

I received an inquiry from my customer regarding the MMC1_SDCD and MMC2_SDCD advisory indicated as "Added clarification notes to MMC1_SDCD and MMC2_SDCD signals about pulled down requirement" on the datasheet (p4, 12, and 150)

Can you tell me the reason behind this? 

MMC1_SDCD is for card detection and shorts to GND when inserted at SW in connector. Therefore, it is not possible to determine that the card is not inserted unless it is pulled up on the board. Looking at EVM PROC078A(001)_SCH.PDF, it is pulled up to VSYS_IO_3V3 by R86.

Best regards,

Mari Tsunoda

  • 0
    TI__Intellectual 1230 points

    Hi Mari,

    During boot, the ROM code checks the status of the card detect pin (SDCD, pin P23).  It must be low to indicate card detected if booting from SD card. 

    An external pull-down resistor is required on this pin if the memory device in use does not support card detect, or if the pin is unconnected for any other reason. For memory devices which do support card detect, a pull-up resistor (such as in the EVM schematic) indicates a default state of no card present.

    Regards,

    Marco