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Altera_Forum's avatar
Altera_Forum
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14 years ago

DDR2 -CYCLONE IV Termination

Hello

I am designing a board which contains a DDR2 SDRAM memory and a CYCLONE IV device.

I looked at the development kit of CYCLONE IV schematics and saw that all the signals from/to the ddr2 have an external parralel 50 ohm termination to vtt(0.9v).

I read some of the threads regarding the subject but they are quite ambiguous..I don't have enough space on my board so I would love to get a clear answer to the following questions:

  1. Is the external termination resistor neccecarry ? Can it be ommited from all the signals? If not- what signals still must have the external termination?

  2. What is the correct INTERNAL OCT (for the CYCLONE device) which can replace the external termination?

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    I'm already have a my board with Cyclone IV and DDR2 - it already worked without termination. Micron's article says that you don't need termination resistors if you have length less then 62.5 mm.

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    hi,

    I have also a small board with cyclone IV / DDR2.

    When you say that DDR2 works without termination, is it only for dq/dqs or for all signals² : diff clocks, addresses and command signals ?

    I also see on cyclone III dev kit that FPGA vref IO (VREFBxNy) are connected to DDR_vref. Is it needed ?

    thanks.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    You have to place termination resistor only for diff clock.

    FPGA vref IO connect to DDR_VREF ( = 1.8V/2) due to io standard used DDR2.

    Also you have to read ALtera documents about using DDR more carefully