The DS1602 is a real time clock/elapsed time counter designed to count seconds when VCC power is applied and continually count seconds under battery backup power with an additional counter regardless of the condition of VCC. The continuous counter can be used to derive time of day, week, month, and year by using a software algorithm. The VCC powered counter will automatically record the amount of time that VCC power is applied. This function is particularly useful in determining the operational time of equipment in which the DS1602 is used. Alternatively, this counter can also be used under software control to record real time events. Communication to and from the DS1602 takes place via a 3wire serial port. A 1-byte protocol selects read/ write functions, counter clear functions and oscillator trim. A low cost 32.768 kHz crystal attaches directly to the X1 and X2 pins. If battery powered-only operation is desired, the VBAT pin must be grounded and the VCC pin must be connected to the battery.