SDram refresh interval

Discussion in 'VHDL' started by KnowNothing, Aug 5, 2008.

  1. KnowNothing

    KnowNothing

    Joined:
    Aug 5, 2008
    Messages:
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    I am hoping someone here can help me with this question. Is this posted in the correct place?

    My receiver uses a TM4M16SD-70 sdram. Which I believe is 8 meg.

    According to the STI5518 Register Manual the Memory Interval is set by writing to the VID_CFG_MCF register. It states the following example for to determine the value to use:

    If 2048 rows must be refreshed every 32 ms for a SDRAM clock of 100MHz, the following value must be stored:

    32 * ( .001/2048 ) * (100000000/24) = 65

    In my case:
    If 8 meg of rows must be refreshed every X ms for a SDRAM clock of 121.5MHz, where X = 32 ms (I think, is this correct for this chip?)
    it uses the following formula:

    interval = ((121500 * 500 decimal - 1280 decimal) >> 12 decimal) and 127 decimal

    (">>" means to shift result 12 bits to the right)

    I am trying to understand what the different values in this formula represent.
    I know that 121500 is the frequency determined by the formula:
    frequency = clock frequency / 1000 where clock frequency = 121500000 hz

    can anybody explain what the other values represent?
    500 = ?
    1280 = ?

    How does this formula relate to the other formula?
    Last edited: Aug 5, 2008
    KnowNothing, Aug 5, 2008
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