Abstract: A buffer circuit for programming an I/O pin of a programmable logic device to function either as a normal I/O site, a power pin, or a ground pin has been provided. The I/O pin may be programmed by a user by simply placing first and second control signals in appropriate logic states. The buffer circuit also includes a tri-state circuit for providing tri-state outputs when functioning as a normal I/O site.

Abstract: The output signal of a CMOS power-on reset circuit changes state upon detecting a predetermined threshold of the power supply voltage during the start-up transient. During the power-up of the power supply voltage, the output signal of the power-on reset circuit ramps up with the power supply voltage until the latter reaches a first predetermined level whereat a control signal begins to track the increasing power supply voltage, less two diodes potentials. Upon reaching the turn-on potential of a transistor, the control signal activates an inverter to substantially reduce the output signal signifying that the power supply voltage level is sufficient for the operation of external circuitry. The output signal then disables the current flowing through the power-on reset circuit to save power consumption.