Questions about Spartan 3A

[Patrick Maupin]

1) Has anybody designed a board that will work with all members of the
Spartan3A family in an FT256? Do you use any special pin programming
on, for example an XC3S400A, to keep it from pulling excessive current
when it's in the transition region because it's connected to VCCINT
(because that pin site is a VCCINT pin in an XC3S700A/XC321400A)?
Also, it seems like the extra startup current (before configuration)
for all the XC3S700A/XC3S1400A VCCINT/GND pins which are I/O pins in
an XC3S400 would be in the range of 10 mA or so for the XC3S400. Does
that sound about right?

2) The Spartan 3A documentation states that LVDS output can only be
used on banks 0 and 2. It also states that internal 100 ohm LVDS
receive termination is only available on pins that are output pins,
but it doesn't explicitly state whether this includes output pins in
banks 1 and 3, or whether "output" in this context means "pins which
are capable of LVDS output" (which would only include pins in banks 0
and 2).

I suppose for question 2 I can fairly easily fire up ISE and find the
answer. Maybe I'll do that tomorrow.

Thanks,
Pat

[John Adair]

Our Craignell2 DIL module http://www.enterpoint.co.uk/component_replacements/craignell2.html
has been built with FPGA parts from the XC3S200A to XC3S1400A in the
FTG256 package. We did to confirm that we didn't have pinning issues.
We didn't bother with the XC3S50A because it caused to many issues
with pins in the design. I think the XC3S700A and XC3S1400A were
afterthoughts in the family and hence the power pin moves on those
parts. The derivative development board product Drigmorn2 is being
built with XC3S700A but we will probably build it with other chip fits
for OEM customers.

Whilst these boards were not built to support LVDS we avoided a lot of
pin problems by not using pins that become input only on any of the
variants. This does cut down the usable pins a lot and one of my pet
hates of an otherwise good family. Interestingly Spartan-6 looks a lot
better in this respect and we put a lot LVDS support into Drigmorn3
the next member of the family. For LVDS output you are restricted to
banks 0 and 2. For inputs use any bank. We have not had any problems
with excessive power either.

John Adair
Enterpoint Ltd. - Home of Drigmorn2. The Spartan-3A Starter Board.

[Patrick Maupin]

On Dec 19, 4:21 am, John Adair <g...@enterpoint.co.uk> wrote:
> Our Craignell2 DIL modulehttp://www.enterpoint.co.uk/component_replacements/craignell2.html

Thanks for the quick reply!

I think my board will probably support the 50 on up, simply because
I'm not going to try to make that many pins available. (But, at the
end, I might do like you and give up on it -- that remains to be
seen.)

Best regards,
Pat