Rainbow Electronics DS1691 User Manual

www.dalsemi.com

DS1688/DS1691

3 Volt/5 Volt Serialized Real Time Clock

with NV RAM Control

FEATURES

Incorporates industry standard DS1287 PC clock
plus enhanced features:

 +3 or +5V operation
 64–bit Silicon serial number
 64–bit customer specific ROM or additional

serial number available

 Power control circuitry supports system

power on from date/time alarm or key closure

 Automatic battery backup and write

protection to external SRAM

 Crystal select bit allows RTC to operate with

6 pF or 12.5 pF crystal

 114 bytes user NV RAM
 Auxiliary battery input
 RAM clear input
 Century register
 32 kHz output for power management
 32–bit V
 32–bit V
 16–bit power cycle counter
 Compatible with existing BIOS for original

DS1287 functions

 Available as IC (DS1688) or stand–alone

module with embedded battery and crystal
(DS1691)

 Timekeeping algorithm includes leap year

compensation valid up to 2100

powered elapsed time counter

CC

powered elapsed time counter

BAT

PIN ASSIGNMENT

PIN DESCRIPTION

X1 - Crystal Input
X2 - Crystal Output

RCLR - RAM Clear Input

AD0-AD7 - Mux’ed Address/Data Bus

PWR - Power-on Interrupt Output
KS - Kickstart Input
CS - RTC Chip Select Input

ALE - RTC Address Strobe

WR - RTC Write Data Strobe

RD - RTC Read Data Strobe

V

CCO

- RAM Power Supply Output

ORDERING INFORMATION

PART # DESCRIPTION

DS1688S RTC IC, 28–pin SOIC
DS1691 RTC Module; 28–pin DIP

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DS1688/DS1691

IRQ - Interrupt Request Output

SQW - Square Wave Output
V

CCI

- +3 or +5V Main Supply
GND - Ground
V
V

BAT
BAUX

- Battery + Supply

- 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 industr y 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 includin g
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 elect ronic all y 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 powe r control cir cuitr y, which allows the s ystem to be po wered 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

and CEO

CCO

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

power through the V

CC

pin. The chip enable out-put to RAM (CEO ) is

CCO

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 th at a
minimum of 10 years of timekeeping and data retention in the absence of V

is guaranteed.

CC

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.

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