# Re: XAUI IO specs

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Mark, Rich,

I will second Rich's request for clarification from the Hari
electrical spec authors.  In Rich's example below, if each of
the two phases swung between +400 mV and -400 mV, then the
"single-ended peak-to-peak" would be 800 mV.  That makes the
"differential peak-to-peak" to be 1600 mV.

Putting it another way, dif'l voltage, Vdifl = Voutpos - Voutneg.
If Voutpos and Voutneg each swing between +/-400 mV, then the
dif'l signal swings between +/-800 mV, yielding 1600 mVp-p.

Vdifl(p-p) = 2 * Vsingle-ended(p-p)
= 4 * Vsingle-ended(zero-peak)

Regards,
Mike

ps:  On rereading Rich's note, if by "positive differential signal"
he meant the difference of two signals, then his description
is the same as mine (but then "referenced to ground" is
confusing, because only single-ended signals are referenced
to anything -- dif'l signals are referenced to each other).
This is the type of confusion that haunts anyone specifying
dif'l signals unless everyone is brutally unambiguous.

Rich Taborek wrote:
>
> Mark,
>
> I'll have to defer to Mr. Ali Ghiasi and Mr. Richard Dugan on this issue to
> properly resolve the nomenclature. My understanding of the parameters listed is
> as follows using Vo Dif(max) 800 mV as an example:
>
> When the Output is set to a logic one, the positive differential signal,
> referenced to a 0 V ground, is a maximum of +400 mV and the negtive differential
> signal, referenced to a 0 V ground, is a maximum of -400 mV.
>
> When the Output is set to a logic zero, the positive differential signal,
> referenced to a 0 V ground, is a maximum of -400 mV and the negtive differential
> signal, referenced to a 0 V ground, is a maximum of +400 mV.
>
> I'd call this V diff peak-to-peak, but this I'm NOT an expert in this area.
>
> Best Regards,
> Rich
>
> --
>
> Mark Kerestes wrote:
> >
> > Rich, Ali
> >  On slide 22 of the XAUI/XGXS Proposal from Albuquerque was listed :
> > Vo Dif(max) 800mV
> > Vo Dif(min) 500mV
> > Vin Dif(max)  1000mV
> > Vin Dif(min) 175mV
> > I assume these are truely Vdif and NOT Vdif peak to peak? I have some
> > confusion from looking back at the
> > Nov 5 1999 "HARI the Electrical Interface" which seems to have a table
> > that mixes Vdif and Vdif peak to peak
> > showing PECL vs LVDS vs HARI side by side.
> > Best regards,
> > Mark
>
> -------------------------------------------------------
> Richard Taborek Sr.                 Phone: 408-845-6102
> Chief Technology Officer             Cell: 408-832-3957
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