DS1994 Memory/Time iButton

Abstract: This application note gives details on techniques for accurate time measurement with the Dallas Semiconductor DS1994 Memory/Time iButton. Significant improvement of timekeeping accuracy can be achieved by using a real-time clock (RTC) with supplemental nonvolatile SRAM for the storage of calibration constants. Whenever the timekeeper is reset, improved calibration constants can be stored in the nonvolatile SRAM, so that successive resets adaptively enhance accuracy. When the timekeeper is read, these constants are supplied along with the uncorrected time-base to a microprocessor program that calculates and displays a more accurate reading. In this way the practical effect of errors from temperature, initial calibration, quartz aging, and shock history can be minimized.