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DS1688/DS1691 3V/5V Serialized Real-Time Clocks with NV RAM Control
www.maxim-ic.com
GENERAL DESCRIPTION
The DS1688/DS1691 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 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.
FEATURES
Incorporates Industry Standard DS1287 PC Clock Plus Enhanced Features: +3V 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 6Pf or 12.5Pf Crystal 114 Bytes User NV RAM Auxiliary Battery Input RAM Clear Input Century Register 32kHz Output for Power Management 32-Bit VCC Powered Elapsed Time Counter 32-Bit VBAT Powered Elapsed Time Counter 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
PIN-PACKAGE 28 SO (0.330) 28 SO (0.330) 28 EDIP (0.740) TOP MARK* DS1688S DS1688S DS1691
PIN CONFIGURATIONS
TOP VIEW
ORDERING INFORMATION
PART DS1688S DS1688S+ DS1691 TEMP RANGE 0C to +70C 0C to +70C 0C to +70C VOLTAGE (V) 3 to 5 3 to 5 3 to 5
+ Denotes a lead-free/RoHS-compliant device. + A "+" anywhere on the top mark denotes a lead-free/RoHS-compliant device.
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REV: 112205
DS1688/DS1691
DETAILED DESCRIPTION
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 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 DS1688/DS1691 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 VCCO and CEO pins. The lithium energy source used to permanently power the RTC 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 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 32.768kHz crystal, and a lithium battery in a complete, selfcontained 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. For a complete description of operating conditions, electrical characteristics, bus timing, and pin descriptions other than the SQW output, refer to the DS1689/DS1693 data sheet, available online at www.maxim-ic.com/DS1689.
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DS1688/DS1691
PIN DESCRIPTION
PIN SO 1 2, 3 4 5-12 13 14, 19 15 16 17 18 20 21 22 23 EDIP 1 -- 4 5-12 13 14 15 16 17 18 20 21 22 -- NAME VBAUX X1, X2 RCLR AD0-AD7 PWR GND KS CS ALE WR RD PSEL IRQ VBAT FUNCTION Auxiliary Battery Supply Crystal Input, Crystal Output Active-Low RAM Clear Input Muxed Address/Data Bus Active-Low Power-On Interrupt Output Ground Active-Low Kickstart Input Active-Low Chip Select Input Address Strobe Active-Low Write Data Strobe Active-Low Read Data Strobe +3V or +5V Power Select Active-Low Interrupt Request Output Battery + Supply Square-Wave Output. This signal functions identical to the DS1689/DS1693 with an exception occurring at power-up. A 32kHz square wave is output on this pin, tREC, after a power-up condition has been detected. This condition sets the following bits, enabling the 32kHz output: DV1 = 1, SQWE = 1, and E32K = 1. The square wave is output on this pin if either SQWE = 1 or E32K = 1. RAM Power-Supply Output +3V or +5V Main Supply Active-Low RAM Chip Enable Out Active-Low RAM Chip Enable In No Connection
24
24
SQW
25 26 27 28 --
25 26 27 28 2, 3, 19, 23
VCCO VCCI CEO CEI N.C.
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DS1688/DS1691
PACKAGE INFORMATION
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.)
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DS1688/DS1691
PACKAGE INFORMATION (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.)
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DS1688/DS1691
PACKAGE INFORMATION (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.)
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Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product. No circuit patent licenses are implied. Maxim/Dallas Semiconductor reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
(c) 2005 Maxim Integrated Products * Printed USA
The Maxim logo is a registered trademark of Maxim Integrated Products, Inc. The Dallas logo is a registered trademark of Dallas Semiconductor Corporation.

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