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Method and circuit for allowing a microprocessor to change its operating frequency on-the-fly

  • US 6,859,884 B1
  • Filed: 04/02/2001
  • Issued: 02/22/2005
  • Est. Priority Date: 10/26/2000
  • Status: Expired due to Term
First Claim
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1. A circuit that allows a processor forming a part of a microcontroller to change its operating frequency, comprising:

  • a clock generator generating a plurality of clock signals at a plurality of frequencies;

    a first switch receiving the plurality of clock signals and selecting one of the clock signals as an output thereof to be the current clock according to a current speed select signal;

    a current speed latch storing the current speed select signal;

    a first phase shifter shifting the phase of the current clock to produce a phase shifted current clock;

    a second switch receiving the plurality of clock signals and selecting one of the clock signals as an output thereof to be the new clock according to a new speed select signal;

    a new speed register storing the new speed select signal;

    wherein, the new speed select signal is produced by the processor and stored in the new speed register;

    a second phase shifter shifting the phase of the new clock to produce a phase shifted new clock; and

    logic means, receiving the current clock, the phase shifted current clock, the new clock, the phase shifted new clock and a signal from the processor directing a speed change as inputs thereto, the logic means for producing a signal latching the new speed into the current speed latch at a point in time after the speed change signal when the current clock, phase shifted current clock, the new clock and the phase shifted new clock have the same state.

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