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8148 memory

William Fischer
Prodigy 10 points


We are in the process of a PCB layout of a video product utilizing the 8148. We are not sure exactly how much DDR2memeory we will require. Is it possible to design the layout for all 8 (2gig) of memory and then only populate 4 pieces if that is all that is needed?

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    TI__Guru**** 393215 points
    Hi William,
     
    Yes, this is possible. However there are some considerations you should have in mind:
     
    One approach is to use only one EMIF in 32-bit mode for the 4-chip configuration. In this case you will need to reconfigure software and enable internal pullup/pulldown resistors on the unused EMIF, as described in sections 4.4 and 8.13.4.1.1.1 of the DM814X Datasheet.
     
    The other approach is to use both EMF's in 16-bit mode. In this case you should make sure that there are no stubs left on the Address/Control/Clock lines when you have only 2 memory chips per EMIF. This means that the DDR chips that are mounted on the PCB should be the ones that are at the end of the Address/Control/Clock lines.
     
    I have information that a customer has successfully implemented the first approach.