Re: XGMII: HSTL Classes
Ted-
Whether your company or some other vendor happens to support a particular
interface specification is just a little too close to a conversation that
could be construed as one that was related "as to how to carve up a market".
i.e. not appropriate for the standards reflector.
Please rephrase.
Thanks
Geoff
At 04:23 PM 9/15/00 -0700, Speers, Ted wrote:
>Regarding the choice of IO standard for XGMII, I'd like to offer the
>following perspective from an FPGA vendor.
>
>Currently, Xilinx supports HSTL Class 1, 3 and 4 but Altera only supports
>HSTL Class 1. Actel does not support HSTL at the moment but, if at all
>possible, would like to ensure that products in the pipeline can support
>XGMII.
>
>If interoperability is a goal, out of the shoot, I'd say you're stuck with
>HSTL Class 1 if you want to make the switch to HSTL from SSTL.
>
>If that's not enough, here's more:
>
>CSIX ( a backplane standards org http://www.csix.org ) has selected HSTL
>Class 1. Might be relevant to the line card board designer ... minimizing
>the IO standards he has to deal with.
>
>The difference among classes is primarily drive strengths which are spec'ed
>to support different termination schemes:
>
>HSTL Class 1: IOH -8, IOL 8
>HSTL Class 2: IOH -16, IOL 16
>HSTL Class 3: IOH -8, IOL 24
>HSTL Class 4: IOH -8, IOL 48
>
>HSTL Class 2 is onerous to support for an FPGA vendor because of the
>required size of the pull-up. Similarly, Class 3 and Class 4 require large
>pull-downs that are expensive to support in a general purpose FPGA.
>
>VCCO for all HSTL classes is 1.5 V +/- 0.1 V. There is no 1.8 volt HSTL
>standard that I am aware of (BTW, I'm not an IO guy so I could be lying
>about all of this stuff).
>
>I also understand that there are other tricky (but not unsolvable) things
>involved with design of the diff amp based around the requirement for a Vref
>(min) of 0.68V. That doesn't give much headroom in 1.5 volt and lower
>technologies.
>
>So, if I was old enough to vote, I would vote for HSTL Class 1 over other
>HSTL standards.
>
>Thx,
>
>Ted Speers
>Sr. Manager, Strategic Marketing
>Actel