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Old 01-14-2004, 06:45 PM
Barry Brown
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Default Virtex II - LVDS_33_DCI?

In the Virtex II User Guide (v1.6.1) on pg 200, it states ...

DCI in Virtex-II Hardware
DCI only works with certain single-ended and differential I/O standards. DCI
supports
the following Virtex-II standards:
LVDCI, LVDCI_DV2, GTL_DCI, GTLP_DCI, HSTL_I_DCI, HSTL_II_DCI, HSTL_III_DCI,
HSTL_IV_DCI, SSTL2_I_DCI, SSTL2_II_DCI, SSTL3_I_DCI, and SSTL3_II_DCI,
LVDS_25,
LVD***T_25, LVDS_33_DCI, LVDS_25_DCI, LVD***T_33_DCI , and LVD***T_25_DCI.

Note the reference to LVDS_33_DCI! In several other places I have found it
stated that if you use DCI with LVDS, then you must have Vcco = 2.5V, or it
won't work correctly.

I would like to try DCI with my Virtex II LVDS inputs with Vcco = 3.3V, and
have it work correctly. Can this be done? Or is there a typo in the User's
Guide.



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Old 01-15-2004, 04:14 AM
Brian Davis
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Default Re: Virtex II - LVDS_33_DCI?

Barry wrote:
>
> I would like to try DCI with my Virtex II LVDS inputs with Vcco = 3.3V, and
> have it work correctly. Can this be done? Or is there a typo in the User's
> Guide.
>

The documentation is wrong; the V2 LVDS DCI input terminators only work
at 2.5V, as they are implemented as a split termination between VCCO/GND
on each side of the pair- the common mode LVDS offset voltage will be
way off at VCCO=3.3V

See Xilinx Answer Record 15633 ( but ignore the incorrect 62.5 mW number )

For a handy list of other LVDS_xx_DCI 'features' that await, see also:
http://www.fpga-faq.com/archives/61300.html#61312

Brian
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