Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

DDR2 DQSn Pin Question

Hi, All

I am using Cyclone III and DDR2 as memory, I found there is no DQSn Pin in CycloneIII device. So how to connect DQSn pin in DDR2 memory device. Connect to Vtt=0.9V or GND, or somewhere else?

Thanks

4 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    Hi,

    it depends.

    In DDR2, the DQS signal may either be single ended or differential.

    Take a look in your DDR2 device's datasheet about this.

    If you are using a diferential DQS, then you need to set the DQS signal to the a differential SSTL I/O standard. The DQS_n signal will then be automatically assigned to the proper pin.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    --- Quote Start ---

    Hi,

    it depends.

    In DDR2, the DQS signal may either be single ended or differential.

    Take a look in your DDR2 device's datasheet about this.

    If you are using a diferential DQS, then you need to set the DQS signal to the a differential SSTL I/O standard. The DQS_n signal will then be automatically assigned to the proper pin.

    --- Quote End ---

    But I can not find any DQSn pin in the Cyclone III device, is that means CIII device can not support differential DQS mode?

    Thanks
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    Cyclone III documentation says that Differential SSTL is only supported on dedicated clock input and dedicated PLL output pins.

    Thus, I'm afraid that, no, you can't use a differential DQS in a Cyclone III.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    Unless you make a psudo-diff pin set by taknig the signal and it's inversion - placing them next to each other and adding proper termination on the board. THen it will be a mtter of the speed you are looking to obtain - best to do some PCB simulation with something like HyperLinx to make sure it all works.

    Regards,

    Avatar