Re: Virtex 4 package layout
- From: Gabor <gabor@xxxxxxxxxxx>
- Date: Tue, 19 Feb 2008 12:16:13 -0800 (PST)
On Feb 19, 11:18 am, austin <aus...@xxxxxxxxxx> wrote:
OK, I was WRONG. I am not often WRONG, but, I can be WRONG, and I have
been WRONG in the past.
NC is no connect. We don't use those pins, and they are not connected
internally in V4, and V5.
Sorry for any confusion.
In my experience, NC means no internal connection. DNU means "do not
or "make no external connection." There are many examples of this in
JEDEC standard memories for instance.
I would like to add that Xilinx does a pretty good job of making the
package footprint compatible across the parts that use it. This gets
even better in the V5 series where the smaller parts just leave out
entire banks instead of a spattering of pins within banks. This helps
to maintain I/O functionality when going to a larger device. In
the old devices, the additional I/O's separating the same pins of
the package can cause excessive pin-to-pin timing when upgrading
to a larger device. As one who works with board-level products,
I've seen a number of headaches involved with making the FPGA size
a customer option. With some vendors it was almost impossible to
find a DDR memory pinout that works across the device range of a given
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