Digital clock switching means

Details Digital clock switching means Digital clock switching means

2007-11-20

2007-11-20

Wells, Kenneth B. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific signal discriminating without subsequent control

By pulse width or spacing

C327S099000

Reexamination Certificate

active

11386916

ABSTRACT:
A digital clock switching circuit and method is disclosed and is operable to deadlock-free switch a digital clock source for an integrated circuit. The circuit includes a first finite state machine associated with a first clock source and a second finite state machine associated with a second clock source. The finite state machines are connected to each other and monitor the current state of the other finite state machine. Each finite state machine receives an input select signal to control which clock source should be active and passed to a clock output. Each finite state machine includes a counter, wherein the counter associated with the active clock source is initialized to a first predetermined value when the input select signal indicates a switching off of the active clock source. The finite state machine associated with the active clock source enters a CHECK state and varies a count at each clock cycle. If the other finite state machine verifies a presence of its clock source before the counter reaches a second predetermined value the switch of the active clock source is effected.

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