Patent ID: 7218911

Claim:
A battery operated wireless communication device comprising: a wireless receiver operable to receive radio signals carrying digital messages and to extract the digital messages there from; a reference oscillator operable to produce a reference oscillator clock; a sleep oscillator operable to produce a sleep oscillator clock; and a dual mode timer for continually maintaining system time based upon a reference counter output while operating in an active mode and based upon a sleep counter output when operating in a sleep mode, the dual mode timer including: a reference counter operable to produce the reference counter output based upon the reference oscillator clock and a reference counter modulus when in the active mode; a sleep counter operable to produce the sleep counter output based upon the sleep oscillator clock and a sleep increment value; calibration circuitry to set the sleep increment value prior to the dual mode timer transitioning from the active mode to the sleep mode; a switch coupled to receive the reference counter output and the sleep counter output and that is operable to produce the reference counter output when the dual mode timer is operating in the active mode and to produce the sleep counter output when the dual mode timer is operating in the sleep mode; and a frame counter coupled to receive the output of the switch and a frame counter modulus and operable to produce multi-frame epochs based upon the output of the switch and the frame counter modulus.