FPGA Central

Newbie alert...

I would like to drive my Spartan 3 design with inputs from a 5V source. I've
been unable to find anything in the Spartan 3 datasheet that lets me know if
this is do-able. (The signal will be coming fom the parallel port on my
laptop, which I suspect probably is 3.3V but I want to be on the safe side.)

Any tips are appreciated.

Thanks,

-Nevo

"Nevo" <[email protected]> wrote in message
news:zwrIg.2012$XD1.1382@trnddc01...
> Newbie alert...
>
> I would like to drive my Spartan 3 design with inputs from a 5V source.
> I've been unable to find anything in the Spartan 3 datasheet that lets me
> know if this is do-able. (The signal will be coming fom the parallel port
> on my laptop, which I suspect probably is 3.3V but I want to be on the
> safe side.)
>
> Any tips are appreciated.
>
> Thanks,
>
> -Nevo

I think I wrote this a little too hastily.

I'm using the Digilent Spartan 3 starter board and would like to drive my
design with the parallel port of my computer with as few (hopefully no)
external parts as possible. All the IO banks are using 3.3V reference. If
there's a particular configuration of the I/O pins that could tolerate a 5V
input, I'd appreciate a short explanation. Meanwhile I'll keep reading the
datasheet.

Thx,

-Nevo

"Nevo" <[email protected]> wrote in message
news:zwrIg.2012$XD1.1382@trnddc01...
> Newbie alert...
>
> I would like to drive my Spartan 3 design with inputs from a 5V source.
> I've been unable to find anything in the Spartan 3 datasheet that lets me
> know if this is do-able. (The signal will be coming fom the parallel port
> on my laptop, which I suspect probably is 3.3V but I want to be on the
> safe side.)
>
> Any tips are appreciated.
>
> Thanks,
>
> -Nevo

Hm... I found http://direct.xilinx.com/bvdocs/appnotes/xapp179.pdf, which
lists the 5V tolerant SelectIO standards for the Spartan 2 family (and
implicitly says none of the standards are 5V tolerant in the Spartan 2E
family), but I'm unable to find a simlar reference for the Spartan 3 family.

Table 27, Absoulte Maximum Ratings under DC Electrical Characteristics,
suggests that putting 5V into the chip is a no-no.

Hm; I think I'm going to answer my own question here by pointing myself to
XAPP429 and a whole host of archived messages in comp.arch.fpga.

Nevo wrote:
> "Nevo" <[email protected]> wrote in message
> news:zwrIg.2012$XD1.1382@trnddc01...
> > Newbie alert...
> >
> > I would like to drive my Spartan 3 design with inputs from a 5V source.
> > I've been unable to find anything in the Spartan 3 datasheet that lets me
> > know if this is do-able. (The signal will be coming fom the parallel port
> > on my laptop, which I suspect probably is 3.3V but I want to be on the
> > safe side.)
> >
> > Any tips are appreciated.
> >
> > Thanks,
> >
> > -Nevo
>
> Hm... I found http://direct.xilinx.com/bvdocs/appnotes/xapp179.pdf, which
> lists the 5V tolerant SelectIO standards for the Spartan 2 family (and
> implicitly says none of the standards are 5V tolerant in the Spartan 2E
> family), but I'm unable to find a simlar reference for the Spartan 3 family.
>
> Table 27, Absoulte Maximum Ratings under DC Electrical Characteristics,
> suggests that putting 5V into the chip is a no-no.
>
> Hm; I think I'm going to answer my own question here by pointing myself to
> XAPP429 and a whole host of archived messages in comp.arch.fpga.

You need some sort of interface if you want to use 5V I/O with the
Spartan 3. You have lots of options.

Leon

A 390-Ohm series resistor normally works ok. If you look at the starter
kits that use Spartan3E you see that all the 5V stuff has this to connect to
the FPGA.

If you don't fancy that then you can get a dedicated IC, like an LCX125...
Beware that they're fairly slow, the resistor is better IMHO.
http://www.fairchildsemi.com/ds/74/74LCX125.pdf

Good luck.

Ben


"Leon" <[email protected]> wrote in message
news:[email protected] oups.com...
>
> Nevo wrote:
>> "Nevo" <[email protected]> wrote in message
>> news:zwrIg.2012$XD1.1382@trnddc01...
>> > Newbie alert...
>> >
>> > I would like to drive my Spartan 3 design with inputs from a 5V source.
>> > I've been unable to find anything in the Spartan 3 datasheet that lets
>> > me
>> > know if this is do-able. (The signal will be coming fom the parallel
>> > port
>> > on my laptop, which I suspect probably is 3.3V but I want to be on the
>> > safe side.)
>> >
>> > Any tips are appreciated.
>> >
>> > Thanks,
>> >
>> > -Nevo
>>
>> Hm... I found http://direct.xilinx.com/bvdocs/appnotes/xapp179.pdf, which
>> lists the 5V tolerant SelectIO standards for the Spartan 2 family (and
>> implicitly says none of the standards are 5V tolerant in the Spartan 2E
>> family), but I'm unable to find a simlar reference for the Spartan 3
>> family.
>>
>> Table 27, Absoulte Maximum Ratings under DC Electrical Characteristics,
>> suggests that putting 5V into the chip is a no-no.
>>
>> Hm; I think I'm going to answer my own question here by pointing myself
>> to
>> XAPP429 and a whole host of archived messages in comp.arch.fpga.
>
> You need some sort of interface if you want to use 5V I/O with the
> Spartan 3. You have lots of options.
>
> Leon
>

Nevo schrieb:

> Hm; I think I'm going to answer my own question here by pointing myself to
> XAPP429 and a whole host of archived messages in comp.arch.fpga.
Right. Like this one:
http://groups.google.com/group/comp....8bfdaf324cb93e
(First google groups hit for "5v spartan-3")

So just use a series resistor.

Kolja Sulimma

Nevo wrote:

> "Nevo" <[email protected]> wrote in message
> news:zwrIg.2012$XD1.1382@trnddc01...
>> Newbie alert...
>>
>> I would like to drive my Spartan 3 design with inputs from a 5V source.
>> I've been unable to find anything in the Spartan 3 datasheet that lets me
>> know if this is do-able. (The signal will be coming fom the parallel
>> port on my laptop, which I suspect probably is 3.3V but I want to be on
>> the safe side.)
>>
>> Any tips are appreciated.
>>
>> Thanks,
>>
>> -Nevo
>
> Hm... I found http://direct.xilinx.com/bvdocs/appnotes/xapp179.pdf, which
> lists the 5V tolerant SelectIO standards for the Spartan 2 family (and
> implicitly says none of the standards are 5V tolerant in the Spartan 2E
> family), but I'm unable to find a simlar reference for the Spartan 3
> family.
>
> Table 27, Absoulte Maximum Ratings under DC Electrical Characteristics,
> suggests that putting 5V into the chip is a no-no.
>
> Hm; I think I'm going to answer my own question here by pointing myself to
> XAPP429 and a whole host of archived messages in comp.arch.fpga.

Nevo, i applaud your ability to post (partial) answers to your own
questions. More people need that ability. It shows the ability to
recognize when you have bypassed the limits of your sure knowledge; and the
perseverance to continue seeking yourself, instead of passively waiting for
"an/the answer".

--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.Â*Â*
--Schiller

On 2006-08-27 20:33:55 -0700, "Nevo" <[email protected]> said:

> Hm... I found http://direct.xilinx.com/bvdocs/appnotes/xapp179.pdf,
> which lists the 5V tolerant SelectIO standards for the Spartan 2 family
> (and implicitly says none of the standards are 5V tolerant in the
> Spartan 2E family), but I'm unable to find a simlar reference for the
> Spartan 3 family.

Hmm indeed. I'm glad you mentioned this, because I'd assumed the 2E and
the 2 had the same 5v-tolerance characteristics... Having read
ds077.pdf (Spartan-2E) as *well* as ds001.pdf (Spartan-2), I now
realise my error...

Looks like I'll be using a -2 rather than a -2E for my
interface-to-ancient-bus-logic :-)

Cheers,
Simon