[SI-LIST] SSO of a Spartan3 in a PQ208 package
- From: <henrik@xxxxxxxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 20 Mar 2006 19:05:56 +0100
Hi!=0D
=0D
As a hobby I'm designing a graphics card for the atari computers containing=
a=0D
Spartan3 (XC3S400) that will implement a 16-bit DDR1 interface at 166MHz=0D
(DDR333). I know I've asked you about this board before (but not this parti=
cular=0D
question), but new questions keep coming up. I hope you have patience with =
me. :-)=0D
=0D
I've chosen the PQ208 package for my prototype because I want to be able to=
=0D
solder this board myself without paying for mounting a BGA package (like th=
e=0D
FT256). Now I'm concerned about the SSO limitations of the PQ208 package. T=
he=0D
datasheet says that only 4 outputs of type SSTL2 class 1 or 2 outputs of ty=
pe=0D
SSTL2 class 2 would be able to switch in the same direction at the same tim=
e=0D
without problems, but I wonder if I can avoid this limitation by splitting =
up the=0D
outputs into groups of four pins where each group would switch a few hundre=
d=0D
picoseconds from the other group. This would result in two groups per bank =
(8=0D
data pins for each bank). When switching 4 SSTL2 class 1 outputs in a bank =
would=0D
the power rail in the package be so heavily loaded that even waiting 500ps =
until=0D
switching the next 4 outputs wouldn=E2=80=99t be possible without the signa=
ls being=0D
severly affected? I=E2=80=99m asking for your general feeling about this, s=
hould I give=0D
it a try or just forget it?=0D
=0D
=0D
=0D
Thanks=0D
=0D
/Henrik Gild=C3=A5=0D
=0D
=0D
=0D
=0D
=0D
=0D
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