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Registered: ‎07-23-2014

Correct electrical connection for unidirectional LVDS signals for AUX signal with DisplayPort LogiCORE



I'm currently looking at the DisplayPort LogiCORE on a Spartan-6 and am trying to understand how the dual uni-directional interface for the AUX channel works.



From the "LogiCORE IP DisplayPort v3.2 Product Guide" on page 110;
> The core has been designed as unidirectional LVDS_25, requiring two pin pairs.
> The output AUX signal is 3-state controlled. The board should be designed to
> combine these signals external to the FPGA.


What is the correct way to electrically combined these two pin pairs? I have not been able to find any examples of this configuration.


This method also seems like a strange way to impliment a bi-directional LVDS signal. Normally with LVDS you want a point-to-point link and this seems to be fraught with danger. Does anyone know what limitations ended up with this being used? Looking at newer versions of the core, it seems like on a Series-7 device it is now possible to use a single bi-directional pair?



The document also mentions that on a Spartan-6 device, it is optional to use the DISPLAY_PORT IOSTANDARD and instead you can use the two pin pairs as described above with the LVDS_25 IOSTANDARD. When doing this, is it possible to use the LVDS_33 IOSTANDARD (for the AUX pairs) rather than the LVDS_25 IOSTANDARD? The Spartan-6 documentation mentions in multiple places that LVDS_33 and LVDS_25 are electrically identical.



Thank you for your help.


Tim 'mithro' Ansell


Tim 'mithro' Ansell
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