fpgaftdijtagxilinx
I have some boards with Xilinx Spartan 3 FPGAs, I would like to upload new bitstreams over JTAG. I was planning on using UrJTAG.
I already have a couple of FTDI based JTAG adapters for ARM targets – can these be used?
They run at 3V3, I read that the Xilinx JTAG is at 2V5 will this be a problem?
Alternatively, I have a few FTDI FT232s, is there a simple cable I could build?
I have decided to go with the Bus Blaster, because it looks like the most flexible and inexpensive JTAG adaptor out there. It features a CPLD which does most of the work and can be re-programmed also.
I'd go for anything Video (especially HD video) related:
One of favourite FPGA projects of a friend of mine, http://nsa.unaligned.org/, used HD transform boards.
Another of my personal favourites that I abused a bit myself, is a BlackMagick Intensity HD capture card, coming with a nice set of video peripherals, a decent microcontroler, and an Spartan 3.
After some abuse, it's probably the cheapest non-academic devkit for PCI/PCIe work on FPGA. It seems to be going new for $120-$150 on ebay these days, and you can probably score one with damaged video interface chips.
Best Answer
You'll want a look at Xilinx app note 453, title "The 3.3V Configuration of Spartan-3 FPGAs". Basically the advice is putting resistors in series to limit the current through the protection diodes, and one over the 2.5V to sink the remaining current. Using level shifting circuitry instead would also work.