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Altera_Forum
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12 years ago

Externally clocking ALTLVDS with a large number of channels

I'm attempting to fit a 29 channel ALTLVDS clocked by an external PLL into a EP4SGX70HF35C2 Stratix IV. I get the following error from the fitter: "Error (176143): Project contains fast PLL driving 29 SERDES transmitters, but target device can contain only 28 SERDES transmitters per fast PLL"

My question is, once I partition the 29 channel ALTLVDS into two smaller blocks, can I simply add another fast/serial clock output to my existing external PLL, or do I truly need to use another PLL?

5 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    In the SIV handbook search on the table "LVDS Channels Supported in Stratix IV GX Device Row I/O Banks". I assume you're in the 1152 package, which supports 56 TX channels. The problem is that half of them are on the left side and half on the right. The PLLs on the left only drive the left channels and same for right side. So you will physically need two PLLs to drive that many channels. Is it one device that really needs 29 or multiple devices(unlikely since it's an odd number). If it is multiple, then you can split them. If one device, maybe you don't need one of the I/O? I had one user not hook up the LSB.

  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    Yeah, you're correct on the package. This makes sense. Thanks.

    The device is a dual-port 14-bit dac, so 28 pairs for data and one for clock. I feel like driving it with 2 PLLs may be asking for trouble, so dropping the lsb is an option.
  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    In altlvds, did you say 28 channels or 29? I thought the clock was a separate LVDS input driving the PLL, and you'd be able to get 29 data channels?

  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    Sorry for the confusion. The DAC (AD9739A) provides a clock that I'm feeding to the PLL. However, you also provide a DDR clock in sync with the data back to the DAC. I was using the "Transmitter outclock" in ALTLVDS Transmitter Settings to generate this clock. So I specified 28 channels in MegaWizard, but it needs 29 transmitters, and I assumed the 29th is for the clock.

  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    Sorry, I was thinking you were receiving data, which would work, but you're right that a 29th is needed for data. Hopefully dropping the LSB works?