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Altera_Forum
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13 years ago

Cyclone V LVDS & DDR3 on same bank

Hello,

I am planning to use a Cyclone V 5CGTFD7D5F31 with the following requirements;

- 32 bit DDR3 interface Top and Bottom (64 bit total)

- 68 LVDS input pairs

Once I have assigned pins to the HMC for the DDR3 interfaces I am left with the following available LVDS RX pairs per bank;

3A: 8

3B: 6

4A: 5

5A: 8

5B: 12

6A: 20

7A: 5

8A: 14

Total: 78

The HMC uses banks 3B, 4A, 7A & 8A, so I will need to have both LVDS and DDR3 signals in these same banks.

Here’s the crunch:

DDR3 requires that VCCIO is set to 1.5V, while LVDS requires that VCCIO is set to 2.5V. VCCPD should be 2.5V in both cases (table 5-1).

From C5 handbook, Vol 2:

Page 5-2; “VCCPD powers the LVDS input buffers”.

Page 5-12; LVDS Input RD OCT; “You can use RD OCT when you set both the VCCIO and VCCPD to 2.5 V.”

So, assuming that the LVDS input buffers are powered from VCCPD = 2.5V, can I use the LVDS differential inputs if VCCIO is set to 1.5V fro DDR3?

Also, can I use RD OCT?

If not, can I do it with external RD?

Any guidance would be greatly appreciated!

Thanks, Ken

12 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    Hello!

    Still can't clearly understood, it is possible to use true LVDS transmit and receive (without using external resistors) in the bank with Vccio=1.8v, Vccpd=2.5?

    According this topic, it's impossibleю

    But i Create simple project in Quartus 15, compile it without errors.

    According Cyclone V Device Handbook update from June 2013 2013.06.17

    "Updated the topic about LVDS input RD OCT to remove the require‐

    ment for setting the VCCIO to 2.5 V. RD OCT now requires only that

    the VCCPD is 2.5 V."

    Somebody tell me who to believe? Quartus or Forum?

    Thank in advance!
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor

    Hi KWler,

    In the end we used a bigger device and did not have LVDS mixed with DDR3 so the issue went away...

    Sorry I can't be of more help.