DS1685/DS1687
3V/5V Real-Time Clocks
www.maxim-ic.com
FEATURES
Incorporates Industry-Standard DS1287 PC Clock
plus Enhanced Features Such as: Y2K Compliant
+3V or +5V Operation
64-Bit Silicon Serial Number
Power-Control Circuitry Supports System
Power-On from Date/Time Alarm or Key
Closure
32kHz Output for Power Management
Crystal-Select Bit Allows RTC to Operate with
6pF or 12.5pF Crystal
SMI Recovery Stack
242 Bytes Battery-Backed NV RAM
Auxiliary Battery Input
RAM Clear Input
Century Register
Date Alarm Register
Compatible with Existing BIOS for Original
DS1287 Functions
Available as Chip (DS1685) or Stand-Alone
Encapsulated DIP (EDIP) with Embedded
Battery and Crystal (DS1687)
Timekeeping Algorithm Includes Leap-Year
Compensation Valid Through 2099
Underwriters Laboratory (UL) Recognized
APPLICATIONS
Embedded Systems
Utility Meters
Security Systems
Network Hubs, Bridges, and Routers
PIN CONFIGURATIONS
TOP VIEW
PWR
X1
X2
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
GND
1
2
24
23
V
CC
X2
X1
PWR
N.C.
V
CC
SQW
PWR
1
2
3
4
5
6
7
8
9
10
11
12
24
V
CC
SQW
V
BAUX
RCLR
N.C.
IRQ
KS
RD
N.C.
WR
ALE
CS
DS1685/
3
DS1685S/
22
4
DS1685E
21
5
6
7
8
9
10
11
12
20
19
18
17
16
15
14
13
V
BAUX
RCLR
V
BAT
IRQ
KS
RD
GND
WR
ALE
CS
AD0
AD1
AD2
AD3
AD4
AD5
N.C.
5
6
7
8
9
V
BAUX
SQW
N.C.
N.C.
RCLR
V
BAT
IRQ
KS
RD
GND
WR
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
GND
DS1687
23
22
21
20
19
18
17
16
15
14
13
4
3
2
1
28
27
26
25
24
23
22
21
20
19
DS1685Q
10
11
12
13 14
15 16
17
18
DIP (0.600″)/
SO (0.300″)/
TSSOP (0.173″)
AD6
N.C.
AD7
GND
CS
ALE
N.C.
PLCC
EDIP (0.740″)
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REV: 112105
DS1685/DS1687 3V/5V Real-Time Clocks
ORDERING INFORMATION
PART*
DS1685-3
DS1685-3+
DS1685-5
DS1685-5+
DS1685-5IND
DS1685-5IND+
DS1685E-3
DS1685E-3+
DS1685E-5
DS1685E-5+
DS1685EN-3
DS1685EN-3+
DS1685EN-5
DS1685EN-5+
DS1685E-3/T&R
DS1685E-3+T&R
DS1685E-5/T&R
DS1685E-5+T&R
DS1685EN-3/T&R
DS1685EN-3+T&R
DS1685EN-5/T&R
DS1685EN-5+T&R
DS1685Q-3
DS1685Q-3+
DS1685Q-5
DS1685Q-5+
DS1685QN-3
DS1685QN-3+
DS1685QN-5
DS1685QN-5+
DS1685QN-5/T&R
DS1685Q-3/T&R
DS1685Q-3+T&R
DS1685Q-5/T&R
DS1685Q-5+T&R
DS1685S-3
DS1685S-3+
DS1685S-5
TEMP RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
VOLTAGE
(V)
3
3
5
5
5
5
3
3
5
5
3
3
5
5
3
3
5
5
3
3
5
5
3
3
5
5
3
3
5
5
5
3
3
5
5
3
3
5
PIN-PACKAGE
24 DIP (0.600”)
24 DIP (0.600”)
24 DIP (0.600”)
24 DIP (0.600”)
24 DIP (0.600”)
24 DIP (0.600”)
24 TSSOP (0.173”)
24 TSSOP (0.173”)
24 TSSOP (0.173”)
24 TSSOP (0.173”)
24 TSSOP (0.173”)
24 TSSOP (0.173”)
24 TSSOP (0.173”)
24 TSSOP (0.173”)
24 TSSOP (0.173”)/Tape & Reel
24 TSSOP (0.173”)/Tape & Reel
24 TSSOP (0.173”)/Tape & Reel
24 TSSOP (0.173”)/Tape & Reel
24 TSSOP (0.173”)/Tape & Reel
24 TSSOP (0.173”)/Tape & Reel
24 TSSOP (0.173”) /T&R
24 TSSOP (0.173”) /T&R
28 PLCC
28 PLCC
28 PLCC
28 PLCC
28 PLCC
28 PLCC
28 PLCC
28 PLCC
28 PLCC/Tape & Reel
28 PLCC/Tape & Reel
28 PLCC/Tape & Reel
28 PLCC/Tape & Reel
28 PLCC/Tape & Reel
24 SO (0.300”)
24 SO (0.300”)
24 SO (0.300”)
TOP MARK*
DS1685-3
DS1685-3
DS1685-5
DS1685-5
DS1685-5
DS1685-5
DS1685E-3
DS1685E-3
DS1685E
DS1685E
DS1685E-3
DS1685E-3
DS1685E
DS1685E
DS1685E-3
DS1685E-3
DS1685E
DS1685E
DS1685E-3
DS1685E-3
DS1685E
DS1685E
DS1685Q-3
DS1685Q-3
DS1685Q-5
DS1685Q-5
DS1685Q-3
DS1685Q-3
DS1685Q-5
DS1685Q-5
DS1685Q-5
DS1685Q-3
DS1685Q-3
DS1685Q-5
DS1685Q-5
DS1685S-3
DS1685S-3
DS1685S-5
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DS1685/DS1687 3V/5V Real-Time Clocks
PART*
DS1685S-5+
DS1685SN-3
DS1685SN-5
DS1685SN-5/T&R
DS1685S-3/T&R
DS1685S-3+T&R
DS1685S-5/T&R
DS1685S-5+T&R
DS1687-3
DS1687-3+
DS1687-5
DS1687-5+
DS1687-3IND
DS1687-3IND+
DS1687-5IND
DS1687-5IND+
TEMP RANGE
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
VOLTAGE
(V)
5
3
5
5
3
3
5
5
3
3
5
5
3
3
5
5
PIN-PACKAGE
24 SO (0.300”)
24 SO (0.300”)
24 SO (0.300”)
24 SO (0.300”)/Tape & Reel
24 SO (0.300”)/Tape & Reel
24 SO (0.300”)/Tape & Reel
24 SO (0.300”)/Tape & Reel
24 SO (0.300”)/Tape & Reel
24 EDIP (0.740”)
24 EDIP (0.740”)
24 EDIP (0.740”)
24 EDIP (0.740”)
24 EDIP (0.740”)
24 EDIP (0.740”)
24 EDIP (0.740”)
24 EDIP (0.740”)
TOP MARK*
DS1685S-5
DS1685S-3
DS1685S-5
DS1685S-5
DS1685S-3
DS1685S-3
DS1685S-5
DS1685S-5
DS1687-3
DS1687-3
DS1687-5
DS1687-5
DS1687-3
DS1687-3
DS1687-5
DS1687-5
+ Denotes a lead-free/RoHS-compliant device. A “+” anywhere on the top mark indicates a lead-free/RoHS-compliant device.
*
An “N” or “IND” denotes an industrial temperature grade device.
TYPICAL OPERATING CIRCUIT
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DS1685/DS1687 3V/5V Real-Time Clocks
DETAILED DESCRIPTION
The DS1685/DS1687 are real-time clocks (RTC) designed as successors to the industry-standard DS1285,
DS1385, DS1485, and DS1585 PC RTCs. These devices provide 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 to 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 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 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
EDIP. 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 3V/5V Real-Time Clocks
PIN DESCRIPTIONS
PIN
DS1685
DIP, SO,
TSSOP
PLCC
DS1687
EDIP
Active Low Power-On Output, Open Drain. The
PWR
pin is intended for use
as an on/off control for the system power. With V
CC
voltage removed from
the DS1685/DS1687,
PWR
can be automatically activated from a kickstart
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. The voltage of the pullup supply should be no greater than
5.5V.
No Connection. Pins missing by design.
Connections for 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.
Multiplexed, Bidirectional Address/Data Bus. 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/DS1687 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 portion 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 extended RAM.
Ground
Chip-Select Input, Active-Low. The chip-select signal must be asserted low
during a bus cycle for the RTC portion of the DS1685/DS1687 to be
accessed.
CS
must be kept in the active state during
RD
and
WR
timing.
Bus cycles that take place with ALE asserted but without asserting
CS
will
latch addresses. However, no data transfer will occur.
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.
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.
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.
NAME
FUNCTION
1
2
1
PWR
—
1, 11, 13,
18
3
2, 3, 16,
20
—
N.C.
2
X1
3
4
—
X2
4–11
5–10, 12,
14
4–11
AD0–AD7
12, 16
15, 20
12
GND
13
16
13
CS
14
17
14
ALE
15
19
15
WR
17
21
17
RD
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