DS1685_DS1687.pdf

www.maxim-ic.com

DS1685/DS1687

3V/5V Real-Time Clock

www.maxim-ic.com

FEATURES

Incorporates industry-standard DS1287 PC clock

plus enhanced features:

PIN ASSIGNMENT (Top View)

Y2K-compliant

PWR

AD0

V CC

SQW

V BAUX

RCLR

V BAT

IRQ

GND

+3 or +5V operation

64-bit silicon serial number

Power-control circuitry supports system

power-on from date/time alarm or key

closure

AD1

AD2

Crystal-select bit allows RTC to operate with

6pF or 12.5pF crystal

AD3

AD4

AD5

AD6

SMI Recovery Stack

242 bytes user NV RAM

AD7

GND

ALE

Auxiliary battery input

RAM clear input

Century register

DS1685 24-Pin DIP

DS1685S 24-Pin SO (300mil)

DS1685E 24-Pin TSSOP

Date alarm register

Compatible with existing BIOS for original

DS1287 functions

Available as chip (DS1685) or standalone

module with embedded battery and crystal

(DS1687)

PWR

V CC

N.C.

SQW

V BAUX

Timekeeping algorithm includes leap-year

compensation valid up to 2100

N.C.

AD0

Underwriters Laboratory (UL) recognized

RCLR

N.C.

AD1

Package Dimension Information

http://www.maxim-ic.com/TechSupport/DallasPackInfo.htm

AD2

IRQ

AD3

AD4

AD5

AD6

4 3 2 1 28 27 26

AD0

AD1

AD2

AD3

AD4

AD5

RCLR

V BAT

IRQ

GND

AD7

ALE

GND

N.C.

DS1687 24-Pin Module PDIP (740mil)

12 13 14 15 16 17 18

DS1685Q 28-Pin PLCC

Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device

may be simultaneously available through various sales channels. For information about device errata, click here: http://www.maxim-ic.com/errata .

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080202

32kHz output for power management

DS1685/DS1687

ORDERING INFORMATION

PART

PIN-PACKAGE

VOLTAGE

(V)

TOP MARK

TEMP RANGE

DS1685-3

24 DIP

DS1685-3

0°C to +70°C

DS1685-5

24 DIP

DS1685-5

0°C to +70°C

DS1685-5IND

24 DIP

DS1685-5*

-40°C to +85°C

DS1685E-3

24 TSSOP

DS1685E-3

0°C to +70°C

DS1685E-5

24 TSSOP

DS1685E

0°C to +70°C

DS1685EN-3

24 TSSOP

DS1685E-3*

-40°C to +85°C

DS1685EN-5

24 TSSOP

DS1685E*

-40°C to +85°C

DS1685E-3/T&R

24 TSSOP/

Tape and Reel

DS1685E-3

0°C to +70°C

24 TSSOP/

Tape and Reel

DS1685E-5/T&R

DS1685E

0°C to +70°C

24 TSSOP/

Tape and Reel

DS1685EN-3/T&R

DS1685E-3*

-40°C to +85°C

24 TSSOP/

Tape and Reel

DS1685EN-5/T&R

DS1685E*

-40°C to +85°C

DS1685Q-3

24 PLCC

DS1685Q-3

0°C to +70°C

DS1685Q-5

24 PLCC

DS1685Q-5

0°C to +70°C

DS1685QN-3

24 PLCC

DS1685Q-3*

-40°C to +85°C

DS1685QN-5

24 PLCC

DS1685Q-5*

-40°C to +85°C

DS1685QN-5/T&R

24 PLCC/Tape and Reel

DS1685Q-5*

-40°C to +85°C

DS1685Q-3/T&R

24 PLCC/Tape and Reel

DS1685Q-3

0°C to +70°C

DS1685Q-5/T&R

24 PLCC/Tape and Reel

DS1685Q-5

0°C to +70°C

DS1685S-3

24 SO

DS1685S-3

0°C to +70°C

DS1685S-5

24 SO

DS1685S-5

0°C to +70°C

DS1685SN-3

24 SO

DS1685S-3*

-40°C to +85°C

DS1685SN-5

24 SO

DS1685S-5*

-40°C to +85°C

DS1685SN-5/T&R

24 SO/Tape and Reel

DS1685S-5*

-40°C to +85°C

DS1685S-3/T&R

24 SO/Tape and Reel

DS1685S-3

0°C to +70°C

DS1685S-5/T&R

24 SO/Tape and Reel

DS1685S-5

0°C to +70°C

DS1687-3

24 PDIP Module

(740mil)

DS1687-3

0°C to +70°C

24 PDIP Module

(740mil)

DS1687-5

0°C to +70°C

24 PDIP Module

(740mil)

DS1687-3IND

DS1687-3*

-40°C to +85°C

24 PDIP Module

(740mil)

DS1687-5IND

DS1687-5*

-40°C to +85°C

*An “N” located in the right-hand corner of the top of the package denotes an industrial device.

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DS1685/DS1687

TYPICAL OPERATING CIRCUIT

DESCRIPTION

The DS1685/DS1687 is a real-time clock (RTC) designed as a successor to the industry-standard

DS1285, DS1385, DS1485, and DS1585 PC RTCs. This device provides the industry-standard DS1285

clock function with either +3.0V or +5.0V operation. The DS1685 also incorporates a number of

enhanced features including a silicon serial number, power-on/off control circuitry, 242 bytes of user NV

SRAM, and 32.768kHz output for sustaining power management activities.

The DS1685/DS1687 power-control circuitry allows the system t o be powered on by an external stimulus

such as a keyboard or by a time and date (wake-up) alarm. The PWR output pin can b e trig gered 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 DS1685 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 DS1687 incorporates the DS1685 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

DS1685/DS1687. The following paragraphs describe the function of each pin.

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DS1685/DS1687

SIGNAL DESCRIPTIONS

GND, V CC – DC power is provided to the device on these pins. V CC is the +3V or +5V input.

SQW (Square-Wave Output) - The SQW pin provides a 32kHz square-wave output, t REC , after a power-

up condition has been detected. This condition sets the following bits, enabling the 32kHz output;

DV1 = 1, and E32K = 1. A square wave is output on this pin if either SQWE = 1 or E32K = 1. If E32K =

1, then 32kHz is output regardless of the other control bits. If E32K = 0, then the output frequency is

dependent on the control bits in register A. The SQW pin can output a signal from one of 13 taps

provided by the 15 internal divider stages of the RTC. The frequency of the SQW pin can be changed by

programming Register A as shown in Table 2. The SQW signal can be turned on and off using the SQWE

bit in register B or the E32K bit in extended register 4Bh. A 32kHz SQW signal is output when the

enable-32kHz (E32K) bit in extended register 4Bh is a logic 1 and V CC is above V PF . A 32kHz square

wave is also available when V CC is less than V PF if E32K = 1, ABE = 1, and voltage is applied to the

V BAUX pin.

AD0–AD7 (Multiplexed Bidirectional Address/Data Bus) – Multiplexed buses save pins because

address information and data information time-share the same signal paths. The addresses are present

during the first portion of the bus cycle and the same pins and signal paths are used for data in the second

portion of the cycle. Address/data multiplexing does not slow the access time of the DS1685 since the bus

change from address to data occurs during the internal RAM access time. Addresses must be valid prior

to the latter portion of ALE, at which time the DS1685/D S168 7 latches the address. Valid write data must

be present and held stable during the latter portion of the WR pulse. In a read cycle, the DS1685/DS1687

outputs 8 bits of data during the latter po rtio n of the RD pulse. The read cycle is terminated and the bus

returns to a high-impedance state as RD transitions high. The address/data bus also serves as a

bidirectional data path for the external extended RAM.

ALE (RTC Address-Strobe Input; Active High) – A pulse on the address strobe pin serves to

demultiplex the bus. The falling edge of ALE causes the RTC address to be latched within the

DS1685/DS1687.

RD (RTC Read Input; Active Low ) - RD identifies the time period when the DS1685/DS1687 drives

the bus with RTC read data. The RD signal is an enable signal for the output buffers of the clock.

WR (RTC Write Input; Active Low) - The WR signal is an active-low signal. The WR signal defines

the time period during which data is written to the addressed register.

CS (RTC Chip-Select Input; Active Low) – The chip-select signa l m ust be asserted low during a bus

cycle f or t he R TC portion of the DS1685/DS1687 to be accessed. CS must be kept in the act ive state

during RD and WR timing. Bus cycles that take place with ALE asserted but without asserting CS latch

addresses. However, no data transfer occurs.

IRQ (Interrupt-Request Output; Open Drain, Active Low) – The IRQ pin is an a ctiv e-low output of

the DS1685/DS1687 that can be connected to the interrupt input of a processor. The IRQ output remains

low as long as the status bit causing the interrupt is present and the corresponding interrupt-enable bit is

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DS1685/DS1687

set. To clear the IRQ pin, the application software must clear all enabled flag bits contributing to IRQ ’s

active state.

When no interrupt conditions are present , th e IRQ le vel is in the high-impedance state. Multiple

interrupting devices can be connected to an IRQ bus. The IRQ pin is an open-drain output and requires an

external pullup resistor. The voltage on the pullup supply should be no greater than V CC + 0.2V.

PWR (Power-On Output; Open Drain, Active Low) – The PWR pin is intended for use as a n on/off

control for the system power. With V CC voltage rem ov ed from the DS1685/DS1687, PWR can be

automatically activated from a kic kstar t input by the KS pin or from a wake-up interrupt. Once the

system is powered on, the state of PWR can be controlled by bits in the Dallas registers. The PWR pin

can be connected through a pullup resistor to a positive supply. For 5V operation, the voltage of the

pullup supply should be no greater than 5.7V. For 3V operation, the voltage of the pullup supply should

be no greater than 3.9V.

KS (Kickstart Input; Active Low) – When V CC is removed fro m the DS1685/DS1687, the system can

be powered on in response to an active-low transition on the KS pin, as might be generated from a key

closure. V BAUX must be p res ent and the auxiliary-battery enable bit (ABE) must be set to 1 if the ki ck start

function is used, and the KS pin must be pulled up to the V BAUX supply. While V CC is applied, the KS pin

can be used as an interrupt input.

RCLR (RAM Clear Input; Active Low) – If enabled by software, taking RCLR low clears th e 242

bytes of user RAM. When enabled, RCLR can be activated whether or not V CC is present. The RCLR

function is designed to be used by a human interface (shorting to ground manually or by a switch) and not

to be driven with external buffers. This pin is internally pulled up. Do not use an external pullup resistor

on this pin.

V BAUX – Auxiliary battery input required for kickstart and wake-up features. This input also supports

clock/ calendar and user RAM if V BAT is at lower voltage or is not present. A standard +3V lithium cell or

other energy source can be used. Battery voltage must be held between +2.5V and +3.7V for proper

operation. If V BAUX is not going to be used it should be grounded, and auxiliary-battery enable bit bank 1,

See “Conditions of Acceptability” a t http://www.maxim-ic.com/TechSupport/QA/ntrl.htm .

DS1685 ONLY

X1, X2 – Connections for a standard 32.768kHz quartz crystal. For greatest accuracy, the DS1685 must

be used with a crystal that has a specified load capacitance of either 6pF or 12.5pF. The crystal-select

(CS) bit in Extended Control Register 4B is used to select operation with a 6pF or 12.5pF crystal. The

crystal is attached directly to the X1 and X2 pins. There is no need for external capacitors or resistors.

Note: X1 and X2 are very high-impedance nodes. It is recommended that they and the crystal be guard-

ringed with ground and that high-frequency signals be kept away from the crystal area.

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