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AM335x DDR_RESET Termination

Prad1
Genius 3825 points

Hi,

Regarding the DDR3 "DDR_RESET" recommended termination.

The AM335x Schematic checklist here mentions as
"do not connect DDR_RESET or DDR_CKE to VTT termination resistors. These should be
connected directly between AM335x and DDR."

But in case of startekit EVM here(page 7) DDR_RESETn seems to be connected to VTT_DDR.
Could you please let me know which is the correct way.

Will it be ok to connect like(connected to VDDS_DDR) this below.

Best Regards

prad

  • 0
    TI__Guru**** 393215 points
    Hi Prad,
     
    The Schematic Checklist is correct. You probably have an old Starterkit schematic. In the latest SK schematic both DDR_RESET or DDR_CKE aren't connected to VTT termination resistors.
  • 0 in reply to Biser Gatchev-XID
    TI__Guru**** 393215 points

    One more comment: DDR_RESET does have a pullup resistor to VDDS_DDR and DDR_CKE has a pulldown to GND. These are needed to hold the lines when processor is not active/in low-power mode.

  • 0 in reply to Biser Gatchev-XID
    Genius 3825 points

    Hi Biser,

    Thank you so much...

    In case of the latest schematics here(dated :Friday, March 22, 2013)
    DDR_RESET is connected to VTT_DDR(through R1532) as shown below,
    and there is description saying DNI. Does it mean No Connection?

    And will be ok to pull up the RESET pin of the DDR memory to VDDS_DDR
    as per the StarterKit Schematics (Below).

    Apart from this I need one more advice on the terminations,
    as you can see our customer's circuit above, they have connected
    DDR_CASN,DDR_A0 to DDR_A14, DDR_RASN,DDR_BA....etc pins to VTT_DDR
    as per the StarterKit Schematics.
    But apart form that they have also connected few by-pass capacitors which is not
    there in the StarterKit Schematics.
    If possible could you please let me know will it be ok to use such by-pass capacitors with
    the terminations.


    Best Regards.
    Prad

  • 0 in reply to Prad1
    TI__Guru**** 393215 points
    Yes, DNI means Do Not Insert.
    Yes, pulling up DDR_RESETn to VDDS_DDR is correct.
    Yes, the bypass capacitors are OK on Vtt.