Having a home-made PCB board which can adopt to both Spartan-3A XC3S200A and XC3S400A FPGAs in the same FBGA320 footprint, we are having great troubles getting the 400A image of the logic to work stable, while the 200A image seems to work perfectly with the same logic. The symptoms are that various bits or groups of bits seem to "hang" whenever we try to get them on the uController Bus for reading etc..
We have tried using both Xilinx ISE 8.2 and 9.1 as Fitter, but with the same non-stable, although *different* result in respect of which bits cannot be reached.
The 3 I/Os being the difference between the two Spartan-3A variants are *not* connected in the PCB. Voltages are correct, and the timing should absolutely be no problem in the design (Fmax 4 times over). We have no troubles loading the FPGA devices in two different configurations. The problems seems consistent among boards with the same FPGA - 200A or 400A.
- Have you heard of such problems...?
- Or do you just have some type of clue...?
Thanks in advance,