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DS1691
3 Volt/5 Volt serialized real time clock with NV RAM control
FEATURESIncorporates industry standard DS1287 PC clock
plus enhanced features:+3 or +5V operation64–bit Silicon serial number64–bit customer specific ROM or additional
serial number availablePower control circuitry supports system
power on from date/time alarm or key closureAutomatic battery backup and writeprotection to external SRAMCrystal select bit allows RTC to operate with
6 pF or 12.5 pF crystal114 bytes user NV RAMAuxiliary battery inputRAM clear inputCentury register32 kHz output for power management32–bit VCC powered elapsed time counter32–bit VBAT powered elapsed time counter16–bit power cycle counterCompatible with existing BIOS for original
DS1287 functionsAvailable as IC (DS1688) or stand–alone
module with embedded battery and crystal(DS1691)Timekeeping algorithm includes leap year
compensation valid up to 2100
ORDERING INFORMATION
PART # DESCRIPTIONDS1688S RTC IC, 28–pin SOIC
DS1691 RTC Module; 28–pin DIP
PIN ASSIGNMENT
PIN DESCRIPTION- Crystal Input- Crystal Output
RCLR- RAM Clear InputAD0-AD7- Mux’ed Address/Data Bus
PWR- Power-on Interrupt Output- Kickstart Input- RTC Chip Select Input
ALE- RTC Address Strobe- RTC Write Data Strobe- RTC Read Data Strobe
VCCO- RAM Power Supply Output
DS1688/DS1691
3 Volt/5 Volt Serialized Real Time Clock
with NV RAM Control
DS1688/DS1691
IRQ- Interrupt Request Output
SQW- Square Wave Output
VCCI- +3 or +5V Main Supply
GND- Ground
VBAT- Battery + SupplyVBAUX- Auxiliary Battery Supply
PSEL- +3 or +5V Power Select
CEI- RAM Chip Enable In
CEO- RAM Chip Enable Out
DESCRIPTIONThe 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 writeprotection 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 anadditional 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 PWRoutput pin
can be triggered by one or either of these events, and can be used to turn on an external power supply.
The PWRpin 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 abattery 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 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 aminimum of 10 years of timekeeping and data retention in the absence of VCC is guaranteed.
For a complete description of operating conditions, electrical characteristics, bus timing, and pin
DS1688/DS1691
SIGNAL DESCRIPTION
SQW (Square Wave Output) – The SQW output signal functions identical to the DS1689/DS1693 withan exception occurring at power–up. A 32 kHz square wave will be output on this pin, tREC, after a
power–up condition has been detected. This condition sets the following bits enabling the 32 kHz output;
DV1=1, SQWE=1, and E32K=1. The square wave will be output on this pin if either SQWE=1 or
E32K=1.
DS1688S 28-PIN SOIC
DS1688/DS1691
DS1691 28-PIN 740 MIL MODULE
:
www.ic-phoenix.com
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