DS17885

The DS17885/DS17887 are real-time clocks (RTCs) designed as successors to the industry standard DS1285, DS1385, DS1485, DS1585, and DS1685 PC real-time clocks. These devices provide the industry standard DS1285 clock function with either +3V or +5V operation. The DS17885 also incorporates a number of enhanced features including a silicon serial number, power-on/off control circuitry, 114 bytes of user NV SRAM plus 8kB of additional NV RAM, and 32.768kHz output for sustaining power management activities.

The DS17885/DS17887 power-control circuitry allows the system to be powered on by an external stimulus such as a keyboard or by a time-and-date (wake-up) alarm. The PWR output pin is triggered by one or either of these events, and is used to turn on an external power supply. The PWR pin is under software control, so that when a task is complete, the system power can then be shut down.

The DS17885 is a clock/calendar chip with the features described above. An external crystal and battery are the only components required to maintain time-of-day and memory status in the absence of power. The DS17887 incorporates the DS17885 chip, a 32.768kHz crystal, and a lithium battery in a complete, self-contained timekeeping module. The entire unit is fully tested at Dallas Semiconductor such that a minimum of 10 years of timekeeping and data retention in the absence of VCC is guaranteed.