A clock switching circuit switches between clock signals generated by a local clock unit and those generated by a-system clock unit when disabling, and then subsequently enabling, the system clock unit. The clock switching circuit includes a plurality-of switching circuits that are arranged and configured...http://www.google.de/patents/US5479648?utm_source=gb-gplus-sharePatent US5479648 - Method and apparatus for switching clock signals in a fault-tolerant computer system
