The DS1689/DS1693 is a real time clock (RTC) designed as a successor to the industry standard DS1285, DS1385, DS1485, and DS1585 PC real time clocks. This device provides the industry standard DS1285 clock function with the new feature of either +3.0 or +5.0V operation and automatic backup and write protection to an external SRAM. The DS1689 also incorporates a number of enhanced features including a silicon serial number, power-on/off control circuitry, and 114 bytes of user NVSRAM, power-on elapsed timer, and power cycle counter.
Each DS1689/DS1693 is individually manufactured with a unique 64-bit serial number as well as an additional 64-bit customer specific ROM or serial number. The serial number is programmed and tested at Dallas to insure that no two devices are a like. The serial number can be used to electronically identify a system for purposes such as establishment of a network node address or for maintenance tracking. Blocks of available numbers from Dallas Semiconductor can be reserved by the customer.
The serialized RTCs also incorporate power control circuitry, which allows the system to be powered on via an external stimulus, such as a keyboard or by a time and date (wake-up) alarm. The PWR output pin can be triggered by one or either of these events, and can be 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 DS1689/DS1693 incorporates a power-on elapsed time counter, a power-on cycle counter, and a battery powered continuous counter. These three counters provide valuable information for maintenance and warranty requirements.
Automatic backup and write protection for an external SRAM is provided through the VCCO and CEO pins. The lithium energy source used to permanently power the real time clock is also used to retain RAM data in the absence of VCC power through the VCCO pin. The chip enable output to RAM (CEO) is controlled during power transients to prevent data corruption.
The DS1689 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 DS1693 incorporates the DS1689 chip, a 32.768 kHz 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.
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