Sticking with the same idea as the PIC microcontroller 5×5 board, I have decided to make a 5×5 FPGA board. The chip is a Xilinx Spartan3E (XC3S100E, XC3S250E or XC3S500E) in a VQ100 package. The design is based of the Open Source Papilio One from the Gadget Factory. I have taken their circuit and simplified it by removing the FT2232. I recently built up a Dangerous Prototypes Bus Blaster v4 which already uses the FT2232 and can program FPGAs using UrJTAG. The board breaks out 51 I/O pins as well as 6 pin JTAG. It has 5V, 3.3V, 2.5V and 1.2V linear regulators and a 4MB SPI Flash for bitstream retention. I used the same trick for selecting the power adapter polarity as the 5x5PIC. By removing the USB circuitry and moving the PCB to the very cheap 5×5, I can build one of these for about $22 (Qty 1) as opposed to the $49 retail price tag on the Papilio One.
The PCB design is finished and sent off to Seeed Studio in China for manufacturing. I’ll update when the boards arrive!
Boards and parts arrived from Seeed Studio, Newark and DigiKey. Assembling was a little bit nerve-wracking with the 100-pin $15 FPGA right at the center. I’ll be carefully checking for shorts before plugging this one in.
I initially soldered the FPGA in the wrong orientation! It’s important to note that the big circle is NOT pin 1! The little circle on the opposite corner is pin 1. Powering it on like this didn’t fry the FPGA and I was able to unsolder and rotate.