DP RX 1.4 Subsystem AUX IO Configuration

[vincenttrinh]

Hi,

There are two options for this AUX IO configuration: "Internal" and "External".

I was wondering what the pros and cons were for using either one.  From a board level point of view, it seems the "Internal" configuration is much simpler.

Is there any kind of issue of electrical compliance with the internal version?

[florentw · Accepted solution]

Hi @vincenttrinh 

We just identified an issue with 7-Series / Ultrascale/Ultrascale+ devices for which OBUFTDS can cause a glitch on an True Differential buffer (thus with LVDS_25) used as an output.

If using the AUX channel as internal, then the core will toggle the tristate control  of the IOBUFDS and OBUFTDS. This can cause a disruption and for up to 1us you can see a disruption to the true differential buffer's output levels that share the same bank as the IOBUFDS or OBUFTDS buffers.

This issue will be documented in an AR to be published in the coming weeks (AR#61417).

Thus for a more reliable solution, I would recommend using the external configuration. The con will be that you have to add an extra device (as done on the FMC card) to switch the AUX for in and out.

With that said, the AUX channel is only used during the training phase, so once the stream is up you should not see any major disruptions after it and this will be only seen if you are other true differential buffer's output used on the same bank.

Regards