Dim LED's under certain programs

Spartan-3 USB 2.0 Modules
1

Hi,

I use the LED’s on the unit to debug my programs. However, I found that under certain bit files, the LED is also quite dim.

My application requires the FPGA’s output to set the pins hi/lo on another device. This device’s pins are internally pulled high. When the FPGA led is dim, the FPGA cannot pull those down all the way either (although it does go part-way). Is this a defect with my FPGA?

What sort of bug in my verilog could cause such behavior?

Thanks,

2

You should probably check your output pad.txt file to make sure all your pins are mapped correctly. If pins are mapped incorrectly and you end up with contention because of this, leakage current can sometimes cause outputs to do this.

When this happens, the FPGA I/Os are under stress and can be damaged.