The attribute OE_PHASE is used to control the function of Output Enable pin in the Tristate buffer and I/O modules. Its possible values are ACTIVE_LOW and ACTIVE_HIGH.
If OE_PHASE is ACTIVE LOW, then when OE_ENABLE is LOW, the Output = Input, and when OE_ENABLE is HIGH, the Output= High Impedance.
If OE_PHASE is ACTIVE HIGH, then when OE_ENABLE is HIGH, the Output = Input, and when OE_ENABLE = LOW, the Output= High Impedance
For the XC3000, XC4000, XC5200, and Spartan families, the only allowed value of OE_PHASE is ACTIVE_LOW. For XC9500, the only allowed value is ACTIVE_HIGH. For XC9500XL, you can set the value to either ACTIVE_LOW or ACTIVE_HIGH.
