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DDR_STRBEN length

JI JUN SIC
Prodigy 60 points

dm368 evm board schematic note

DDR_STRBEN is trace to DDR memory
for delay compensation
This net is equal to the DDR_CLKP ( or DDR_CLKN )
plus
the length of DDR_DQXX Average Trace length  

EX)

DDR2_____DDR-CCLKP_________R(22 Ohm)________DDR-CLKP________DM368

DDR2_____DDR-DDQxx_________R(22 Ohm)________DDR-DQxx_________DM368

DM368(T9)___DDR-STRBEN___R(10 Ohm)____T-DDR-STRBEN____DM368(T8)

1 . (DDR_STRBEN) = (DDR_CLKP) +  (DDR_DQxx)

2. (DDR_STRBEN + T_DDR_STRBEN)= (DDR_CLKP + DDR_CCLKP  ) +  (DDR-DQxx+DDR-DDQxx)

What is right of 1 and 2?

  • 0
    TI__Expert 5955 points

    According to the figure, your formula number 2 is appropriate for DDR_STRBEN trace length.

    Thanks,

    -Tai

  • 0 in reply to Tai Nguyen
    Expert 1675 points

    it seems that the length is the total length (DM~R + R~DDR).

    however, we can download the allegro file from spectrumdigital.com.

    and found DDR_STRBEN=2128.89+383.08=2511.97Mil.

    But DDR_CLKP = 1590Mil, DDR_DQS0 = 1386Mil.

    according to  the formula 2, strben = 1590 + 1386 = 2976 mil, But not EQUAL to 2511.97Mil

    what's problem???

  • 0 in reply to YJ Liu
    Prodigy 65 points

    The layout file for LeopardBoard365 doesn't satisfy the requirement either.

     (DDR_STRBEN + T_DDR_STRBEN)= (DDR_CLKP + DDR_CCLKP  ) +  (DDR-DQxx+DDR-DDQxx)

     (474.38 + 465.22 )                                 (  460.35 + 476.2 )                    +   ( 460.54  + 476.95 )    

                                                                                                                           DQS1 selected as reference