Circuit for automatically detecting off-chip, crystal or on-chip, RC oscillator option

摘要

A self-configurable clock circuit which automatically detects at power up whether an off-chip crystal oscillator is connected to an integrated circuit including the self-configurable clock circuit, and following such detection generates a system clock signal and a power on reset signal to be used by other circuitry included in the integrated circuit. If the off- chip crystal oscillator is connected to the integrated circuit, then the self-configurable clock circuit provides the system clock signal from a first signal generated from the off-chip crystal oscillator. On the other hand, if the off-chip crystal oscillator is not connected to the integrated circuit, then the self-configurable clock circuit provides the system clock signal from a second signal generated from an on-chip RC oscillator circuit.