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Voyager
Voyager
163 Views
Registered: ‎08-16-2018

Terminations with Artix-7 and SO-DIMM DDR3

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I want to connect a DDR3 SODIMM to an Artix-7. In the AC701 schematic, there are terminations but not fitted. From what I read, I can/should use the internal terminations on the FPGA. I wonder then why they are there... maybe a question that solves no problem, so I will limit my question to:

Can I use a DDR3 SODIMM module with an Artix-7 (clock 400 MHz) with no external terminations?

 

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Voyager
Voyager
112 Views
Registered: ‎02-01-2013

Re: Terminations with Artix-7 and SO-DIMM DDR3

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The AC701 was designed over 5 years ago. The placement of the terminations on that board may have been a simple CYA move. [Consider Your Alternatives. ;-)] There might have been a risk that the internal FPGA terminations weren't adequate.

The current Zynq-7000 SoC and 7 Series Devices Memory Interface Solutions User Guide (UG 586) does not call for external DQ terminations in a DIMM-based DDR interface. Coupled with the fact that the terminations are de-popped on the board you have, I'd say it's safe to eliminate them from a new A7 DDR3 SO-DIMM design.

-Joe G.

 

3 Replies
Voyager
Voyager
113 Views
Registered: ‎02-01-2013

Re: Terminations with Artix-7 and SO-DIMM DDR3

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The AC701 was designed over 5 years ago. The placement of the terminations on that board may have been a simple CYA move. [Consider Your Alternatives. ;-)] There might have been a risk that the internal FPGA terminations weren't adequate.

The current Zynq-7000 SoC and 7 Series Devices Memory Interface Solutions User Guide (UG 586) does not call for external DQ terminations in a DIMM-based DDR interface. Coupled with the fact that the terminations are de-popped on the board you have, I'd say it's safe to eliminate them from a new A7 DDR3 SO-DIMM design.

-Joe G.

 

Moderator
Moderator
105 Views
Registered: ‎11-28-2016

Re: Terminations with Artix-7 and SO-DIMM DDR3

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Hello @johnvivm,

The recommendation is to follow the DDR3 SDRAM Design Guidelines starting on page 192 of UG586.  My signature has a link to the latest version. Here the guidance is to use ODT when writing to the memory, use DCI for the FPGA in HP banks, and to use the IN_TERM option for the FPGA in HR banks. We also recommend to run simulations on the interface to verify your layout and MIG settings. 
ug586_1.PNGug586_2.PNGug586_3.PNG

If you take a look at other 7-Series boards like the VC707, VC709, and the KC705 which all have SODIMMs none of them have termination resistors installed on the DQ bus.

Voyager
Voyager
91 Views
Registered: ‎02-01-2013

Re: Terminations with Artix-7 and SO-DIMM DDR3

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Naturally, since A7's don't have HP banks, you'll be relying on IN_TERM terminations for all of your bidirectional DQ/DQS signals. (The MIG should take care of that for you.)

And be sure to use a tracking regulator to generate your Vref and Vtt voltages--like the one used on the AC701.

-Joe G.