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DDR2 -CYCLONE IV Termination

Altera_Forum
Honored Contributor II
855 Views

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? 

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3 Replies
Altera_Forum
Honored Contributor II
137 Views

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
Honored Contributor II
137 Views

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
Honored Contributor II
137 Views

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
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