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Micron DDR2 at 85 degrees - can EMR2 register be controlled.

Boris Fennema
Intellectual 510 points
Other Parts Discussed in Thread: OMAP-L138

Dear all,

 

We are using a Micron part ( MT47H128M8 family ) and  there is an additional EMR2 register in the data sheet which needs a bit set to allow the higher refresh rate to be used at temperatures above 85 degrees.

How can I tell the OMAP DDR2 controller to set this bit ?

 

All the best,

 

Boris.

  • 0
    TI__Guru** 116100 points

    Hi Boris,

    Please refer the initialization sequence of DDR2 (5th step) in Micron data sheet,

    You can set the E7 bit (EMR2) through LOAD MODE (LM) command,

    You can execute EMR2 register as like MODE REGISTER.

  • 0 in reply to Titusrathinaraj Stalin
    Intellectual 510 points

    What I do not understand is how to execute the LOAD MODE command using the TI DDR2 register interface as per spruh77 chapter.

    Any ideas ?

  • 0 in reply to Boris Fennema
    TI__Guru*** 125430 points

    First, some clarification on that bit...  In normal operation it's the DRAM controller inside the processor that performs all the refreshes, not the DRAM itself.  Along those lines, that particular bit is only applicable for when the DRAM is in self-refresh.  So if you wanted to put the DRAM into self-refresh at a very high temperature, you would be intended to set that bit.  Unfortunately, there's no way to do that on OMAP-L138 since EMRS(2) is not issued as part of the initialization sequence.

    The other case which I expect is more typical, is the case where the temperature is over 85C during the course of normal operation.  In this scenario the refresh rate is handled inside the OMAP-L138 DRAM controller.  So in particular you would modify SDRCR.RR such that the refresh interval is cut in half, which will double your refresh rate.