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092800
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
CC
powered elapsed time counter
32-bit V
BAT
powered elapsed time counter
16-bit power cycle counter
Compatible with existing BIOS for original
DS1287 functions
Available as IC (DS1689) or standalone
module with embedded battery and crystal
(DS1693)
IC is available in industrial temperature
version
Timekeeping algorithm includes leap year
compensation valid up to 2100
ORDERING INFORMATION
PART #
DESCRIPTION
DS1689S
RTC IC, 28-pin SOIC
DS1689SN
RTC IC, 28-pin SOIC IND
DS1693
RTC Module; 28-pin DIP
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
(Open drain)
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
IRQ
- Interrupt Request Output
(Open drain)
SQW
- Square Wave Output
V
CCI
- +3- or +5V Main Supply
GND -
Ground
V
BAT
- Battery + Supply
V
BAUX
- Auxiliary Battery Supply
PSEL
- +3- or +5V Power Select
CEI
- RAM Chip Enable In
CEO
- RAM Chip Enable Out
DS1689/DS1693
3-Volt/5-Volt Serialized Real-Time Clock
with NV RAM Control
www.maxim-ic.com
V
BAUX
DS1689S 28-Pin SOIC
(330-mil)
13
27
1
2
3
4
5
6
7
8
9
10
11
12
14
28
26
25
24
23
22
21
20
19
18
17
15
16
CEI
V
CCO
SQW
V
BAT
IRQ
PSEL
RD
GND
WR
ALE
KS
CS
CEO
V
CCI
X2
AD0
AD2
AD3
AD4
AD5
AD6
AD7
GND
PWR
X1
RCLR
AD1
GND
DS1693 28-Pin Encapsulated Package
(740-mil)
13
27
NC
AD0
AD2
AD3
AD4
AD5
AD6
AD7
GND
PWR
CEI
V
CCO
SQW
NC
IRQ
PSEL
RD
NC
WR
ALE
KS
CS
1
2
3
4
5
6
7
8
9
10
11
12
14
28
26
25
24
23
22
21
20
19
18
17
15
16
NC
RCLR
AD1
V
BAUX
CEO
V
CCI
DS1689/DS1693
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DESCRIPTION
The DS1689/DS1693 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 industry 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 DS1689 also incorporates a number of enhanced features including
a silicon serial number, power-on/off control circuitry, and 114 bytes of user NVSRAM, power-on
elapsed timer, and power cycle counter.
Each DS1689/DS1693 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 electronically 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 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 DS1689/DS1693 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
CCO
and
CEO
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
CC
power through the V
CCO
pin. The chip enable output to RAM (
CEO
) is
controlled during power transients to prevent data corruption.
The DS1689 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 DS1693 incorporates the DS1689 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 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
DS1689/DS1693. The following paragraphs describe the function of each pin.
SIGNAL DESCRIPTIONS
GND, V
CCI
- DC power is provided to the device on these pins. V
CCI
is the +3-volt or +5-volt input.
Five-volt operation is selected when the PSEL pin is at a logic 1. If PSEL is floated or at a logic 0, the
device will be in auto-sense mode and will determine the correct operating voltage based on the V
CCI
voltage level.
PSEL (Power Select Input) - This pin selects whether 3-volt operation or 5-volt operation will be used.
When PSEL is a logic 1, 5-volt operation is selected. When PSEL is a logic 0 or is floated, the device will
be in auto-sense mode and will determine the correct mode of operation based on the voltage on V
CCI
.
DS1689/DS1693
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V
CCO
(External SRAM Power Supply Output) - This pin will be internally connected to V
CCI
when
V
CCI
is within nominal limits. However, during power fail, V
CCO
will be internally connected to the V
BAT
or V
BAUX
(whichever is larger). For 5-volt operation, switch over from V
CCI
to the backup supply occurs
when V
CCI
drops below the larger of V
BAT
and V
BAUX
. For 3-volt operation, switch over from V
CCI
to the
backup supply occurs at V
PF
if V
PF
is less than V
BAT
and V
BAUX
. If V
PF
is greater than V
BAT
and V
BAUX
,
the switch from V
CCI
to the backup supply occurs when V
CCI
drops below the larger of V
BAT
and V
BAUX
.
DS1689/DS1693 BLOCK DIAGRAM Figure 1
SQW (Square Wave Output) - The SQW pin can output a signal from one of 13 taps provided by the 15
internal divider stages of the real time clock. 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. A 32 kHz SQW signal is output when SQWE=1, the Enable 32 kHz (E32K) bit in
extended register 04BH is a logic 1, and V
CC
is above V
PF
. A 32 kHz square wave is also available when
V
CC
is less than V
PF
if E32K=1, ABE=1, and voltage is applied to V
BAUX
.
DS1689/DS1693
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AD0-AD7 (Multiplexed Bi-directional 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 DS1689 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 DS1689/DS1693 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 DS1689/DS1693
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 bi-
directional 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
DS1689/DS1693.
RD
(RTC Read Input; active low) -
RD
identifies the time period when the DS1689/DS1693 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 signal must be asserted low during a bus
cycle for the RTC portion of the DS1689/DS1693 to be accessed.
CS
must be kept in the active state
during
RD
and
WR
timing. Bus cycles, which take place with ALE asserted but without asserting,
CS
will latch addresses. However, no data transfer will occur.
IRQ
(Interrupt Request Output; open drain, active low) - The
IRQ
pin is an active low output of the
DS1689/DS1693 that can be tied 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 enabled flag bits contributing to
IRQ
's active
state.
When no interrupt conditions are present, the
IRQ
level 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 pull-up resistor.
CEI
(RAM Chip Enable Input; active low) -
CEI
should be driven low to enable the external RAM.
CEO
(RAM Chip Enable Output; active low) - When power is valid,
CEO
will equal
CEI
. When
power is not valid,
CEO
will be driven high regardless of
CEI
.
PWR
(Power-on Output; open drain, active low) - The
PWR
pin is intended for use as an on/off
control for the system power. With V
CC
voltage removed from the DS1689/DS1693,
PWR
may be
automatically activated from a Kickstart input via the
KS
pin or from a Wake-up interrupt. Once the
system is powered on, the state of
PWR
can be controlled via bits in the Dallas registers.
DS1689/DS1693
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KS
(Kickstart Input; active low) - When V
CC
is removed from the DS1689/DS1693, 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 Auxiliary Battery Enable bit (ABE) 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.
RCLR
(RAM Clear Input; active low) - If enabled by software, taking
RCLR
low will result in the
clearing of the 114 bytes of user RAM. When enabled,
RCLR
can be activated whether or not V
CC
is
present.
V
BAUX
- Auxiliary battery input required for kickstart and wake-up features. This input also supports
clock/calendar and External NVRAM if V
BAT
is at lower voltage or is not present. A standard +3-volt
lithium cell or other energy source can be used. Battery voltage must be held between +2.5 and +3.7 volts
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=0.
DS1689 ONLY
X1, X2 - Connections for a standard 32.768 kHz quartz crystal. For greatest accuracy, the DS1689 must
be used with a crystal that has a specified load capacitance of either 6 pF or 12.5 pF. The Crystal Select
(CS) bit in Extended Control Register 4B is used to select operation with a 6 pF or 12.5 pF 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 by guard-
ringed with ground and that high frequency signals be kept away from the crystal area.
For more information on crystal selection and crystal layout considerations, please consult Application
Note 58, "Crystal Considerations with Dallas Real Time Clocks." The DS1689 can also be driven by an
external 32.768 kHz oscillator. In this configuration, the X1 pin is connected to the external oscillator
signal and the X2 pin is floated.
V
BAT
- Battery input for any standard 3-Volt lithium cell or other energy source. Battery voltage must be
held between 2.5 and 3.7 volts for proper operation.
POWER-DOWN/POWER-UP CONSIDERATIONS
The real-time clock function will continue to operate and all of the RAM, time, calendar, and alarm
memory locations remain nonvolatile regardless of the level of the V
CCI
input. When V
CCI
is applied to
the DS1689/DS1693 and reaches a level of greater than V
PF
(power fail trip point), the device becomes
accessible after t
REC
, provided that the oscillator is running and the oscillator countdown chain is not in
reset (see Register A). This time period allows the system to stabilize after power is applied.
When PSEL is floating or logic 0, the DS1689 is in autosense mode and 3-volt or 5-volt operation is
determined based on the voltage on V
CCI
. Selection of 5-volt operation is automatically invoked when
V
CCI
rises above 4.5 volts for a minimum of t
REC
. However, 3-volt operation is automatically selected if
V
CCI
does not rise above the level of 4.25 volts. Selection of the power supply input levels requires
150 ms of input stability before operation can commence.
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