DS1689_05 Datasheet, PDF (5/36 Pages) Dallas Semiconductor – 3V/5V Serialized Real-Time Clocks with NV RAM Control

DS1689/DS1693
DETAILED DESCRIPTION
The DS1689/DS1693 are real-time clocks (RTCs) designed as successors to the industry standard
DS1285, DS1385, DS1485, and DS1585 PC real-time clocks. These devices provide the industry
standard DS1285 clock function with the new feature of either +3.0V 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 NV
SRAM, 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 ensure that no two devices are alike. 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.
Customers can reserve blocks of available numbers from Dallas Semiconductor.
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 incorporate 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 V_CCO 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 V_CC power through the V_CCO 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 32.768kHz 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 V_CC is guaranteed.
OPERATION
The block diagram in Figure 1 shows the pin connections with the major internal functions of the
DS1689/DS1693. The following paragraphs describe the function of each pin.
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