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Dynamic ODT Feature, External Termination

Reagan Revisore
Expert 4225 points

All,

On our AM335x reference design we have the DDR_ODT line having external termination, but with the DDR3 interface, we can also enable dynamic ODT. This feature seems to imply that the termination on the ODT line itself is taken care of internally on the 335x, but we still have the external termination.

Is there a discrepancy here, or is there just a misunderstanding of what all the 335x is providing on that line?

-Reagan

  • 0
    TI__Guru**** 393215 points
    Hi Reagan,
     
    Here is a description of the DDR3 ODT input signal, taken from a memory datasheet:
     
    "On-die termination: ODT enables (registered HIGH) and disables (registered LOW) termination resistance internal to the DDR3 SDRAM. When enabled in normal operation, ODT is only applied to each of the following balls: DQ[7:0], DQS, DQS#, and DM for the x8; DQ[3:0], DQS, DQS#, and DM for the x4..."
     
    As you see DDR_ODT is an enable signal for the data lanes termination on the DDR3 side. It is an address/control class signal and needs to have external Vtt termination. Dynamic ODT takes care of the data lanes termination on the AM335X side.