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Question on termination resistor position

Anonymous
Anonymous

Hi All,

 

I would like to ask a question on termination resistor.

 

 

 

 

Is there any requirement that these resistors be placed near

1.      Output pin

2.      Or receiving (input) pin

?

 

Or they can be arbitrarily placed at anywhere on the wire?

 

In the case for DSP-DDR2 connection, I analyzed both for

1.      Address pin termination resistors

2.      Data pin termination resistors

on their

1.      sheet position (on which sheet they are drawn)

2.      PCB physical location

 

And found there is a consistency: if the termination resistor is on the sheet of DSP, then in PCB it is also close to DSP; if it is on the sheet of DDR2, then in PCB it is also close to DDR2.

 

Is this just a coincidence, or a rule I need to follow?

 

   

Thanks,

Zheng

 

  • 0
    Intellectual 475 points

    Hi Zheng,

    I am working with a custom board with a DM8148 connected to four 16bit DDR3 devices.

    We have encountered some issues to access read / write to the memory.

    we are working with a DDR3-1333, if using DDR PLL to 333Mhz, the data R/WR is not working properly

    but at 100Mhz, it almost work properly, sometimes a write affect bad address. 

    I suspect we have some timing issue with addresses lines or maybe termination resistors or DDR3 controller settings.

    May be you have some hints to debug the DDR3 interface.

    Thanks,

  • Anonymous
    0 Anonymous in reply to Jonathan Journo

    Jonathan,

    I am not an expert with memory devices, and I think both the RAM type (DDR3 vs DDR2) and the processor we use are different. I am sorry that I could not give any useful help.

     

    Zheng