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Altera_Forum's avatar
Altera_Forum
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14 years ago

Constraints for placement of LVDS signals on Cyclone III device

Hello,

I'm working on a design with 64 LVDS signals. The Cyclone III I'm working on is a EP3C120F768. Two signals belong to each others (one is a clock output signal and the other is a data in signal). Because we want to use parallel flash for configuration quite a few pins are already used. Banks 2, 3, 4 and 5 are free to use for the LVDS signals.

I wanted to place an output signal directly beside a corresponding input signal but the synthesis tool complained about invalid placement of output pins. Currently I have all output pins on bank 2 and 5 (left and right banks) and the input pins are all located at banks 3 and 4. But I think this placement would be a nightmare for the layouter.

Can anyone give me some hints on what options I have to place pins?

If needed I can upload my current placement file.

Best regards

Martin

2 Replies

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

    Hm, are You sure You're doing 2.5V outputs on LVDS connected banks? It should allow that. Or... Hm, I can't remember, but afaik I had to use LVDS_3E_R for LVDS outputs.

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

    The problem seems to be that the Cyclone III doesn't support output pins at the lower and upper banks. It had nothing to do that input and output pins were placed side by side.