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RM48L952: Is pull-down required in higher EMIF address line

Jani Okker
Expert 3010 points
Part Number: RM48L952

Hi,

Customer is creating a design with RM48L952 and will use EMIF in their application. Configuration will be similar to the TRM example Configuration  described on Figure 17-27.

On this configuration there is pull-down resistors on address lines [18:13]. We've been trying to figure out what is the reason for these pull-downs. Are those mandatory to be there?

  • 0
    TI__Guru**** 196226 points
    Hello Jani,

    If the CSx pins are to be connected and used as EMIF chip select signals, external pull-up resistors should be connected and used as EMIF chip select signals default to an inactive (high) state immediately following reset.

    The EMIF always drive the data bus to the previous write data value when it is idle (data bus parking). The one exception to this behavior occurs after performing an async read operation while the EMIF is in the self-refresh state. In this situation, the read operation is not followed by the EMIF parking the data bus. Instead, the EMIF tri-states the data bus. Therefore, it is not recommended to perform asynchronous read operations while the EMIF is in the self-refresh state, in order to prevent floating inputs on the data bus. External pull-ups should be placed on the 16 EMIF data bus pins (which do not have internal pull-ups) if it is required to perform reads in this situation. The precise resistor value should be chosen so that the worst case combined off-state leakage currents do not cause the voltage levels on the associated pins to drop below the high-level input voltage requirement.

    The address signals don't require a pull-up resistors.

    Regards,
    QJ