DS1685/DS1687
3V/5V Real-Time Clocks
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
V
BAUX
RCLR
V
BAT
IRQ
KS
RD
GND
WR
ALE
CS
AD0
AD1
AD2
AD3
AD4
AD5
N.C.
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
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
5
6
7
8
9
10
4
3
2
1
28
27
26
25
24
23
22
21
20
DS1685Q
11
12
13 14
15 16
17
18
19
PDIP (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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19-5215; Rev 10/12
DS1685/DS1687 3V/5V Real-Time Clocks
ORDERING INFORMATION
PART*
DS1685-3+
DS1685-5+
DS1685-5IND+
DS1685E-3+
DS1685E-5+
DS1685EN-3+
DS1685EN-5+
DS1685E-3+T&R
DS1685E-5+T&R
DS1685EN-3+T&R
DS1685EN-5+T&R
DS1685Q-3+
DS1685Q-5+
DS1685QN-3+
DS1685QN-5+
DS1685Q-3+T&R
DS1685Q-5+T&R
DS1685S-3+
DS1685S-5+
DS1685S-3+T&R
DS1685S-5+T&R
DS1687-3+
DS1687-5+
DS1687-3IND+
DS1687-5IND+
TEMP RANGE
0°C to +70°C
0°C to +70°C
-40°C to +85°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
-40°C to +85°C
-40°C to +85°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
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
VOLTAGE
(V)
3
5
5
3
5
3
5
3
5
3
5
3
0B
PIN-PACKAGE
24 PDIP (0.600”)
24 PDIP (0.600”)
24 PDIP (0.600”)
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”) /T&R
28 PLCC
28 PLCC
28 PLCC
28 PLCC
28 PLCC/Tape & Reel
28 PLCC/Tape & Reel
24 SO (0.300”)
24 SO (0.300”)
1B
TOP MARK*
DS1685-3
DS1685-5
DS1685-5
DS1685E-3
DS1685E
DS1685E-3
DS1685E
DS1685E-3
DS1685E
DS1685E-3
DS1685E
DS1685Q-3
DS1685Q-5
DS1685Q-3
DS1685Q-5
DS1685Q-3
DS1685Q-5
DS1685S-3
DS1685S-5
DS1685S-3
DS1685S-5
DS1687-3
DS1687-5
DS1687-3
DS1687-5
5
3
5
3
5
3
5
3
5
3
5
3
5
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”)
+Denotes a lead(Pb)-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
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 Maxim Integrated such that a minimum of 10 years of timekeeping and data
retention in the absence of V
CC
is guaranteed.
DETAILED DESCRIPTION
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
PDIP,
SO,
TSSOP
PLCC
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 Maxim
Integrated 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.
DS1687
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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DS1685/DS1687 3V/5V Real-Time Clocks
PIN DESCRIPTIONS (continued)
PIN
DS1685
PDIP,
SO,
TSSOP
Kickstart Input, Active Low. When V
CC
is removed from 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 present and the auxiliary-battery enable bit (ABE) and kick-
start enable bit (KSE) must be set to 1 if the kickstart 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. If not used, connect to V
CC
, or to
V
BAUX
if V
BAUX
is used.
Interrupt-Request Output, Open Drain, Active Low. The
IRQ
pin is an
active-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 set. To clear the
IRQ
pin, the application software must clear
all the enabled flag bits contributing to
IRQ’s
active state asserted but
without asserting
CS
latch addresses. However, no data transfer occurs.
Battery Input for Any Standard 3V Lithium Cell or Other Energy Source.
Battery voltage must be held between 2.5V and 3.7V for proper operation.
V
BAT
must be grounded if not used. Diodes should not be placed between
V
BAT
and the battery. See “Conditions of Acceptability” at
www.maximintegrated.com/UL.
RAM Clear Input, Active Low. If enabled by software, taking
RCLR
low
clears the 242 bytes of user RAM to FFh. 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.
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, register 4BH, should be written to 0.
See “Conditions of Acceptability” at
www.maximintegrated.com/UL.
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 3. 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.
DC Power for Primary Power Supply. When V
CC
is applied within the
normal limits, the device sis fully accessible and data can be written and
read. When V
CC
is below V
PF
reads and writes are inhibited.
PLCC
EDIP
DS1687
NAME
FUNCTION
18
22
18
KS
19
23
19
IRQ
20
24
—
V
BAT
21
25
21
RCLR
22
26
22
V
BAUX
23
27
23
SQW
24
28
24
V
CC
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