A clocking system for providing periodic clocking or timing signals for use in an electronic circuit. The system includes a primary clock source, such as a crystal oscillator, that provides periodic clocking or timing signals at a predetermined frequency, and a back-up clock source that is similarly...http://www.google.com/patents/US4667328?utm_source=gb-gplus-sharePatent US4667328 - Clocking circuit with back-up clock source
