Rainbow Electronics DS1691 - Manual (Page 2)

DS1688/DS1691
2 of 4
IRQ - Interrupt Request Output
SQW - Square Wave Output
V
CCI
- +3 or +5V Main Supply
GND - Ground
V
BAT
- Battery + Supply
V
BAUX
- Auxiliary Battery Supply
PSEL - +3 or +5V Power Select
CEI - RAM Chip Enable In
CEO - RAM Chip Enable Out
DESCRIPTION
The DS1688/DS1691 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 +5.0 volt operation and automatic backup and write
protection to an external SRAM. The DS1688 also incorporates a number of enhanced features including
a silicon serial number, power on/off control circuitry, 114 bytes of user NV SRAM, power on elapsed
timer, and power cycle counter.
Each DS1688/DS1691 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 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. Blocks
of available numbers from Dallas Semiconductor can be reserved by the customer.
The serialized RTC’s 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 DS1688/DS1691 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 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 out-put to RAM ( CEO ) is
controlled during power transients to prevent data corruption.
The DS1688 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 DS1691 incorporates the DS1688 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 V
CC
is guaranteed.
For a complete description of operating conditions, electrical characteristics, bus timing, and pin
descriptions other than the SQW output see the DS1689/DS1693 data sheet.