A digital CMOS programmable clock generator

The digital CMOS software programmable clock generator (PCG) was designed as a macro cell to provide quadrature clocks for the Hobbit based Personal Communicators. The PCG produces a highly accurate variable frequency system clock from 20 kHz to 100 MHz (10 kHz to 50 MHz in quadrature), while using a single inexpensive crystal oscillator as a reference. Both the frequency and tolerance of PCG can be programmed by the user. This cell resides inside the system control chip and has a bus interface allowing local storage of programmed data. Control signals which start and stop operation come from a power management portion of the chip. The output frequency can be changed on the fly.<
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