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You better had read AN522 before writing this post. It's full title already suggests that the requested multipoint LVDS interface is well supported by Stratix IV:
"Implementing Bus LVDS Interface in Cyclone III, Stratix III, and
stratix iv Devices"
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Damn, how could you tell I didn't read it ... sheesh ...
So it appears the caveats with respect to LVDS have changed. The Altera LVDS transmitters with SERDES channels cannot be used for this application, because the transmitters can not be tri-stated.
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DIFFIO_TX pin do not support true LVDS differential receivers.
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The BLVDS transmitter uses two single-ended (SE) output buffers with the second output buffer programmed as inverted.
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So what they've changed is you can use the single-ended transmit buffers in the LVDS receivers ... nice trick.
Previously you would have to emulate tri-stateable transmitters with external resistor termination networks (but then they could not operate at high bit-rates). I don't see any comments regarding the fact that these new transmitter buffers are current-output drivers, but its worth looking into it ... I'll have to try this out.
Thanks Frank!
Cheers,
Dave
Honored Contributor
