Patent ID: 7890787

Claim:
A microprocessor programmable clock calibration system comprising: a normally off reference oscillator clock; a normally on calibratable oscillator clock; a programmable processor for providing a calibration command which turns on said reference oscillator clock; a calibration control system responsive to said calibration command for comparing frequencies of said clocks, said processor turning off said reference oscillator clock after the frequencies are compared, wherein the calibration control system includes a first counter to count the reference oscillator clock and a second counter to count the calibratable oscillator clock and the frequencies of the clocks are compared by comparing the counts of the two counters; and a trim circuit responsive to a difference in said clock frequencies for adjusting said calibratable clock towards said reference clock, wherein the trim circuit is driven by the calibration control system and the calibration control system includes a state machine with states of idle, reset calibration logic, enable calibration, wait for counters to stop, compare oscillator clock frequencies and adjust calibratable oscillator clock frequency.