Abstract: An integrated circuit comprises an application-non-specific library cell, externally developed logic circuitry integrated with the library cell, and an up-integration module (UIM) connected to the library cell and to the logic circuitry and providing a two-way interface between the library cell and the logic circuitry and between the library cell and an external device. The logic developed for a prototype system comprising such a library cell in association with external logic circuitry can be integrated into the circuit without requiring any change in its function or in the program code developed for the prototype system.

Abstract: A phase lock loop circuit comprises a variable frequency oscillator having a control input and an output, a divider having an input coupled with the output of the oscillator and an output coupled with the first input of a phase or frequency comparator. The comparator has a second input for a reference frequency (F.sub.REF) and an output coupled with the oscillator control input for providing a signal which is related to the difference in phase or frequency of the signals at the first and second inputs to effect phase locking of the oscillator to the reference signal. A detector provides a switching signal when the control signal falls outside a predetermined range and a switch in the phase lock loop is responsive to the switching signal to open the loop.