Building a board with Spartan 3 FPGA.

Hi, I am trying to build a very simple Spartan3 - based FPGA board.
The idea is to have FPGA + Flash PROM & Jtag header and I/Os.
Nothing else.

I am running into a problem:
Using my DMM, VCCAUX & VCCO seem to be shorted to GND.
At this point I am absolutely sure that they are shorted through the
Xilinx chip.

Does Xilinx chip need to be programmed with some kind of default
configuration, before it can even be powered on?
In other words, should there be some kind of *safety configuration*
programmed into the Flash PROM, prior to applying power to Xilinx FPGA?

If you have any references, links, suggestions, guidelines for putting
a single FPGA chip on a board with nothing other than the basics for
programming it, I would be grateful if you point me to them.

I copied my design from Digilent Spartan3 Starter Kit, getting rid of
all the *starter kit* peripherals there and just leaving the
essentials: JTAG header, Flash PROM, FPGA, expansion  I/Os

Thanks!

no.
DMM is not good to measure but before config the VCCxx pins should take
some normal current, eg not short circuit.

doing a s3 proto is rather simple, just connect the GND, VCCxx, JTAG
and pull PROG_B thats it

Antti

If VccAux appears to be grounded in a powered board, your problems will 
never be with the device.

If VccAux never comes up, there is no configuration to do anything negative 
to your board.

A newly-powered Spartan3 comes up in an innocuous state until the device is 
programmed at which point it does what it's programmed to do.

Check your soldering.  Check your gerbers.  I've seen problems with both 
despite the best attempts of engineers and design software.


"Telenochek" <interpasha@hotmail.com> wrote in message 
news:1148318946.683392.228470@j73g2000cwa.googlegroups.com...
> Hi, I am trying to build a very simple Spartan3 - based FPGA board.
> The idea is to have FPGA + Flash PROM & Jtag header and I/Os.
> Nothing else.
>
> I am running into a problem:
> Using my DMM, VCCAUX & VCCO seem to be shorted to GND.
> At this point I am absolutely sure that they are shorted through the
> Xilinx chip.
>
> Does Xilinx chip need to be programmed with some kind of default
> configuration, before it can even be powered on?
> In other words, should there be some kind of *safety configuration*
> programmed into the Flash PROM, prior to applying power to Xilinx FPGA?
>
> If you have any references, links, suggestions, guidelines for putting
> a single FPGA chip on a board with nothing other than the basics for
> programming it, I would be grateful if you point me to them.
>
> I copied my design from Digilent Spartan3 Starter Kit, getting rid of
> all the *starter kit* peripherals there and just leaving the
> essentials: JTAG header, Flash PROM, FPGA, expansion  I/Os
>
> Thanks!
> 

-----------------------------------
doing a s3 proto is rather simple, just connect the GND, VCCxx, JTAG
and pull PROG_B thats it
------------------------------------
That's exactly whats on my board + Flash PROM.

On a fully working Spartan3 board from Digilent,
when the board is not powered up:
the VCCO and VCCAUX appear to be shorted to GND (using DMM).
Of course, this could be due to low impedance between supplies and GND,
due to high Iq through the FPGA. But the board is not powered at all.

How do I debug the shorts if I can't even test for them?

1) Before you assemble, check for supply and ground shorts.
Too late?
2) Do a visual inspection of soldered TQFP leads with a stereo microscope
If you're doing a BGA instead, it's a much different issue.
Xray inspection of assembled boards would be needed to troubleshoot BGA 
shorts; this inspection is available from most professional assemblers.

"Telenochek" <interpasha@hotmail.com> wrote in message 
news:1148322083.396270.227300@38g2000cwa.googlegroups.com...
> -----------------------------------
> doing a s3 proto is rather simple, just connect the GND, VCCxx, JTAG
> and pull PROG_B thats it
> ------------------------------------
> That's exactly whats on my board + Flash PROM.
>
> On a fully working Spartan3 board from Digilent,
> when the board is not powered up:
> the VCCO and VCCAUX appear to be shorted to GND (using DMM).
> Of course, this could be due to low impedance between supplies and GND,
> due to high Iq through the FPGA. But the board is not powered at all.
>
> How do I debug the shorts if I can't even test for them?
> 

http://xilant.com/content/view/35/2/

EASY - the board as above DOES work, I used it for SPI indirect
programming testing

Antti

> 1) Before you assemble, check for supply and ground shorts.
> Too late?

Its not too late, I have multiple boards for this.
Without FPGA  (TQFP144) chip on board, there aren't any shorts.
I have checked connections with stereo microscope, no solder bridges.

I think the next thing I will try is to assemble everything, but the
FPGA
and verify that everything without FPGA is fine.
Trouble is that FPGA will be harder to solder with all the stuff on the
board already.
But doable.

Thanks!

EASY - the board as above DOES work, I used it for SPI indirect
programming testing
-----------------------------
Very nice but where is the schematic for it?

Thanks!

Telenochek wrote:

>>1) Before you assemble, check for supply and ground shorts.
>>Too late?
>>    
>>
>
>Its not too late, I have multiple boards for this.
>Without FPGA  (TQFP144) chip on board, there aren't any shorts.
>I have checked connections with stereo microscope, no solder bridges.
>
>I think the next thing I will try is to assemble everything, but the
>FPGA
>and verify that everything without FPGA is fine.
>Trouble is that FPGA will be harder to solder with all the stuff on the
>board already.
>  
>
Have you verified where pin 1 is?  I got tripped up a while ago with Xilinx
using a center-of-side pin 1 on CPLD packages but a corner pin 1 on FPGAs.
Really dumb mistake, but pretty easy to do.

Jon

When you say "shorted", how many ohms (without power applied) are you
seeing between VCC* and GND?  Is it a dead short (i.e. a couple of
ohms max), or is it in the ~15 ohms or more category?  If the latter,
it is probably not shorted,  and may just be the unpowered resistance
of the power system (load and/or regulator).  If it is a dead short,
and it does not exist without the devices on the board, then there are
a few options.  Solder bridges or faulty components, or you may have a
mistake in the pinout of one of the devices, and have a device ground
pin tied to the power plane, or vise-versa.

Andy