US005771180A [ii] Patent Number: 5,771,180 [45] Date of Patent: Jun. 23, 1998
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Primary Examiner—-James P. Trammell
Assistant Examiner—Hien Vo
Attorney, Agent, or Firm—Beyer & Weaver, LLP
[57] ABSTRACT
A real time clock includes an oscillator, a digital counter, a temperature sensor, and a digital processor. The digital processor can read the temperature measured by the temperature sensor and utilize this information to generate an adjustment value for the digital counter. The digital counter is coupled to the digital processor and has an adjustment stage which the digital processor writes into in order to compensate for any oscillator error due to temperature variation. The digital processor may also be coupled to memory storing a temperature adjustment look-up table for use in generating the adjustment value. A method of the present invention includes the initial steps of generating an adjustment look-up table and storing it in non-volatile memory. A method of the present invention further includes the ongoing steps of measuring an ambient temperature, generating an adjustment value, adjusting the digital counter to improve the accuracy of the real time clock, and storing a new alarm time for a future adjustment.
30 Claims, 7 Drawing Sheets
