How is the HSWAP pin connected internally? Can I connect the HSWAP pin to VCCAUX?
The HSWAP pin is a dual-purpose pin in Spartan-3E devices, and it has an internal pull-up resistor connected to VCCO_0. However, we recommend using an external 4.7k resistor to pull the HSWAP pin High or Low.
You can connect the HSWAP pin to VCCAUX, but be aware that an internal upper clamp diode is connected to VCCO. Forward-biasing this clamp diode will conduct a reverse current into the VCCO rail, but the current will be limited by the external pull-up to VCCAUX.