DS3234
Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
General Description
The DS3234 is a low-cost, extremely accurate SPI bus
real-time clock (RTC) with an integrated temperature-compensated crystal oscillator (TCXO) and crystal. The
DS3234 incorporates a precision, temperature-compensated voltage reference and comparator circuit to monitor
VCC. When VCCdrops below the power-fail voltage (VPF),
the device asserts the RST output and also disables read
and write access to the part when VCCdrops below both
VPFand V
BAT
. The RST pin is monitored as a pushbutton
input for generating a µP reset. The device switches to the
backup supply input and maintains accurate timekeeping
when main power to the device is interrupted. The integration of the crystal resonator enhances the long-term accuracy of the device as well as reduces the piece-part count
in a manufacturing line. The DS3234 is available in commercial and industrial temperature ranges, and is offered
in an industry-standard 300-mil, 20-pin SO package.
The DS3234 also integrates 256 bytes of battery-backed
SRAM. In the event of main power loss, the contents of
the memory are maintained by the power source connected to the V
BAT
pin. The RTC maintains seconds,
minutes, hours, day, date, month, and year information.
The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the
24-hour or 12-hour format with AM/PM indicator. Two
programmable time-of-day alarms and a programmable
square-wave output are provided. Address and data
are transferred serially by an SPI bidirectional bus.
Applications
Servers Utility Power Meters
Telematics GPS
Benefits and Features
• Highly Accurate RTC with Integrated Crystal and
SRAM Completely Manages All Timekeeping
Functions
• Accuracy ±2ppm from 0°C to +40°C
• Accuracy ±3.5ppm from -40°C to +85°C
• Real-Time Clock Counts Seconds, Minutes, Hours,
Day, Date, Month, and Year, with Leap Year
Compensation Valid Up to 2099
• Digital Temp Sensor Output: ±3°C Accuracy
• Register for Aging Trim
• RST Input/Output
• Two Time-of-Day Alarms
• Programmable Square-Wave Output
• Simple Serial Interface Connects to Most
Microcontrollers
• 4MHz SPI Bus Supports Modes 1 and 3
• Battery-Backup Input for Continuous Timekeeping
• Low Power Operation Extends Battery Backup Run
Time
• Operating Temperature Ranges: Commercial: 0°C to
+70°C, Industrial: -40°C to +85°C
• 300-Mil, 20-Pin SO Package
• Underwriters Laboratories
®
(UL) Recognized
19-5339; Rev 4; 3/15
Ordering Information
Typical Operating Circuit
#
Denotes an RoHS-compliant device that may include lead(Pb)
that is exempt under the RoHS requirements. Lead finish is
JESD97 Category e3, and is compatible with both lead-based
and lead-free soldering processes. A "#" anywhere on the top
mark denotes an RoHS-compliant device.
Underwriters Laboratories Inc. is a registered certification mark
of Underwriters Laboratories Inc.
PART TEMP RANGE
DS3234S# 0°C to +70°C 20 SO DS3234S
DS3234SN# -40°C to +85°C 20 SO DS3234SN
PINPACKAGE
TOP
MARK
V
V
µP
CC
SCLK
MOSI
MISO
SS
RST
PUSH-
BUTTON
RESET
CS
SCLK
DIN
DOUT
RST
N.C.
N.C.
N.C.
N.C.
N.C.
CC
V
CC
DS3234
GND
INT/SQW
32kHz
V
BAT
N.C.
N.C.
N.C.
N.C.
V
PU
DS3234
Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Maxim Integrated | 2www.maximintegrated.com
Absolute Maximum Ratings
Recommended Operating Conditions
(TA= -40°C to +85°C, unless otherwise noted.) (Notes 2, 3)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage Range on Any Pin Relative to Ground......-0.3V to +6.0V
Junction-to-Ambient Thermal Resistance (θ
JA
) (Note 1) ...55°C/W
Junction-to-Case Thermal Resistance (θ
JC
) (Note 1) ........24°C/W
Operating Temperature Range
(noncondensing) .............................................-40°C to +85°C
Junction Temperature......................................................+125°C
Storage Temperature Range ...............................-40°C to +85°C
Lead Temperature (soldering, 10s) .................................+260°C
Soldering Temperature (reflow, 2 times max) ....................+260°C
(See the
Handling, PC Board Layout, and Assembly
section.)
Electrical Characteristics
(VCC= 2.0V to 5.5V, VCC= active supply (see Table 1), TA= -40°C to +85°C, unless otherwise noted.) (Typical values are at VCC=
3.3V, V
BAT
= 3.0V, and TA= +25°C, unless otherwise noted. TCXO operation guaranteed from 2.3V to 5.5V on VCCand 2.3V to 3.8V on
V
BAT
.) (Notes 2, 3)
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer
board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial
.
Supply Voltage
Logic 1 Input CS, SCLK, DIN V
Logic 0 Input CS, SCLK, DIN,
RST
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
VCC 2.0 3.3 5.5
2.0 3.0 3.8
V
BAT
IH
V
2.0V VCC 3.63V -0.3
IL
3.63V < VCC 5.5V -0.3 +0.7
V
0.7 x
V
CC
VCC +
0.3
+0.2 x
V
CC
V
V
Active Supply Current I
Standby Supply Current I
Temperature Conversion Current I
Power-Fail Voltage V
V
(VCC = 2.0V to 5.5V, TA = -40°C to +85°C, unless otherwise noted.) (Notes 2 and 3)
Logic 1 Output, 32kHz
I
OH
I
OH
I
OH
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
VCC = 3.63V 400
V
= 5.5V 700
CC
VCC = 3.63V 120
V
= 5.5V 160
CC
VCC = 3.63V 500
V
= 5.5V 600
CC
2.45 2.575 2.70 V
25 100 nA
0.85 x V
CC
Leakage Current I
BAT
= -500µA
= -250µA
= -125µA
CCA
CCS
CCSCONV
PF
BATLKG
V
OH
SCLK = 4MHz, BSY = 0
(Notes 4, 5)
CS = VIH, 32kHz output off,
SQW output off
(Note 5)
SPI bus inactive, 32kHz
output off, SQW output off
VCC > 3.63V,
3.63V > V
2.7V > (V
(BB32kHz = 1)
CC
CC
> 2.7V,
or V
BAT
) > 2.0V
µA
µA
µA
V
DS3234
Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Maxim Integrated | 3www.maximintegrated.com
Electrical Characteristics (continued)
(VCC= 2.0V to 5.5V, VCC= active supply (see Table 1), TA= -40°C to +85°C, unless otherwise noted.) (Typical values are at VCC=
3.3V, V
BAT
= 3.0V, and TA= +25°C, unless otherwise noted. TCXO operation guaranteed from 2.3V to 5.5V on VCCand 2.3V to 3.8V on
V
BAT
.) (Notes 2, 3)
Electrical Characteristics
(VCC= 0V, V
BAT
= 2.0V to 3.8V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
Logic 0 Output, 32kHz V
Logic 1 Output, DOUT V
Logic 0 Output, DOUT, INT/SQW V
Logic 0 Output, RST V
Output Leakage Current 32kHz,
INT/SQW, DOUT
Input Leakage DIN, CS, SCLK I
RST Pin I/O Leakage I
TCXO (V
Output Frequency f
Frequency Stability vs.
Temperature
Frequency Stability vs. Voltage Δf/V 1 ppm/V
Trim Register Frequency
Sensitivity per LSB
Temperature Accuracy Temp -3 +3 °C
Crystal Aging Δf/f
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
I
= 1mA 0.4 V
OL
I
= -1.0mA 0.85 x V
OH
I
= 3mA 0.4 V
OL
I
= 1.0mA 0.4 V
OL
CC
Output high impedance -1 0 +1 µA
-1 +1 µA
RST high impedance (Note 6) -200 +10 µA
V
= 3.3V or V
CC
BAT
= 3.3V
32.768 kHz
= 2.3V to 5.5V, V
CC
OL
OH
OL
OL
I
LO
LI
OL
= 2.3V to 3.8V, TA = -40°C to +85°C, unless otherwise noted.) (Notes 2 and 3)
BAT
OUT
0°C to +40°C -2 +2
V
= 3.3V or
Δf/f
OUT
CC
= 3.3V
V
BAT
-40°C to 0°C and
+40°C to +85°C
-3.5 +3.5
-40°C 0.7
Δf/LSB Specified at:
+25°C 0.1
+70°C 0.4
+85°C 0.8
After reflow,
OUT
not production tested
First year ±1.0
0–10 years ±5.0
V
ppm
ppm
ppm
Timekeeping Battery Current
(Note 5)
Temperature Conversion Current I
Data-Retention Current I
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
I
BATTC
BATTDR
BATT
V
= 3.4V 1.5 2.3
EOSC = 0, BBSQW = 0,
CRATE1 = CRATE0 = 0
EOSC = 0, BBSQW = 0 400 µA
EOSC = 1 100 nA
BAT
V
= 3.8V 1.5 2.5
BAT
µA
DS3234
Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Maxim Integrated | 4www.maximintegrated.com
Electrical Characteristics
(VCC= 2.0V to 5.5V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
Power-Switch Characteristics
5(TA= -40°C to +85°C)
Capacitance
(TA= +25°C)
SCLK Clock Frequency f
Data to SCLK Setup t
SCLK to Data Hold t
SCLK to CS Setup t
SCLK to Data Valid (Note 7) t
SCLK Low Time t
SCLK High Time t
SCLK Rise and Fall tR, t
CS to SCLK Setup t
SCLK to CS Hold t
CS Inactive Time t
CS to Output High Impedance t
Pushbutton Debounce PBDB 250 ms
Reset Active Time t
Oscillator Stop Flag (OSF) Delay t
Temperature Conversion Time t
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SCL
DC
CDH
CCS
CDD
CL
CH
CC
CCH
CWH
CDZ
RST
OSF
CONV
2.7V ≤ VCC ≤ 5.5V 4
2.0V ≤ V
< 2.7V 2
CC
30 ns
30 ns
30 ns
2.7V ≤ VCC ≤ 5.5V 80
2.0V ≤ V
< 2.7V 160
CC
2.7V ≤ VCC ≤ 5.5V 110
2.0V ≤ V
< 2.7V 220
CC
2.7V ≤ VCC ≤ 5.5V 110
2.0V ≤ V
F
< 2.7V 220
CC
400 ns
2.7V ≤ VCC ≤ 5.5V 100
2.0V ≤ V
< 2.7V 200
CC
400 ns
(Note 8) 40 ns
250 ms
(Note 9) 100 ms
125 200 ms
200 ns
MHz
ns
ns
ns
ns
VCC Fall Time; V
V
PF(MIN)
VCC Rise Time; V
V
PF(MAX)
Recovery at Power-Up t
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
to
PF(MAX)
PF(MIN)
to
t
t
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Capacitance on All Input Pins C
Capacitance on All Output Pins C
VCCF
VCCR
REC
IN
IO
300 µs
0µs
(Note 10) 125 300 ms
(Note 11) 10 pF
Outputs high impedance (Note 11) 10 pF
DS3234
Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Maxim Integrated | 5www.maximintegrated.com
Pushbutton Reset Timing
Power-Switch Timing
Note 2: Limits at -40°C are guaranteed by design and not production tested.
Note 3: All voltages are referenced to ground.
Note 4: Measured at V
IH
= 0.8 x VCCor VIL= 0.2 x VCC, 10ns rise/fall time, DOUT = no load.
Note 5: Current is the averaged input current, which includes the temperature conversion current. CRATE1 = CRATE0 = 0.
Note 6: The RST pin has an internal 50kΩ (nominal) pullup resistor to V
CC
.
Note 7: Measured at V
OH
= 0.8 x VCCor VOL= 0.2 x VCC. Measured from the 50% point of SCLK to the VOHminimum of DOUT.
Note 8: With 50pF load.
Note 9: The parameter t
OSF
is the period of time the oscillator must be stopped for the OSF flag to be set over the voltage range of
0V ≤ V
CC
≤ V
CC(MAX)
and 2.3V ≤ V
BAT
≤ V
BAT(MAX)
.
Note 10: This delay only applies if the oscillator is enabled and running. If the EOSC bit is 1, t
REC
is bypassed and RST immediately
goes high.
Note 11: Guaranteed by design and not production tested.
WARNING: Negative undershoots below -0.3V while the part is in battery-backed mode may
cause loss of data.
RST
V
CC
V
PF(MAX)
V
PF(MIN)
t
VCCF
RST
PB
DB
V
PF
t
RST
V
PF
t
VCCR
t
REC
DS3234
Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Maxim Integrated | 6www.maximintegrated.com
Timing Diagram—SPI Read Transfer
Timing Diagram—SPI Write Transfer
t
CS
CCS
t
SCLK
DIN
DOUT
NOTE: SCLK CAN BE EITHER POLARITY, SHOWN FOR CPOL = 1.
CC
t
DC
W/R
t
t
CL
t
CDH
WRITE ADDRESS BYTE
R
A6
HIGH IMPEDANCE
t
CH
CS
SCLK
t
CC
t
R
t
F
t
F
t
CDZ
t
CDD
A0
D7
READ DATA BYTE
t
CWH
t
D0
CCH
t
CL
t
CDH
WRITE ADDRESS BYTE
DOUT
DIN
t
DC
W/R
t
CH
A6
A0
HIGH IMPEDANCE
D7 D0
WRITE DATA BYTE
Maxim Integrated | 7www.maximintegrated.com
DS3234
Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
DS3234 toc01
VCC (V)
SUPPLY CURRENT (μA)
5.3
4.8
4.32.8
3.3 3.8
50
100
150
125
75
25
0
2.3
RST ACTIVE
INPUTS = GND
BATTERY CURRENT
vs. SUPPLY VOLTAGE
DS3234 toc02
SUPPLY VOLTAGE (V
BAT
)
SUPPLY CURRENT (nA)
3.8
3.3
2.8
1100
2100
1850
2600
2350
1600
1350
850
600
2.3
VCC = 0V
BB32kHz = 0
BBSQW = 1
BBSQW = 0
BATTERY CURRENT
vs. TEMPERATURE
DS3234 toc03
TEMPERATURE (°C)
SUPPLY CURRENT (nA)
80
6040
-20
0
20
700
650
750
800
850
600
-40
V
BAT
= 3.4V
V
BAT
= 3.0V
VCC = 0V
BB32kHz = 0
BBSQW = 0
FREQUENCY DEVIATION
vs. TEMPERATURE vs. AGING VALUE
DS3234 toc04
TEMPERATURE (°C)
FREQUENCY DEVIATION (ppm)
80
60
40
-20
020
25
15
5
-5
-15
-25
-35
65
55
45
35
-45
-40
AGING = -128
AGING = -33
AGING = 127
AGING = 0
AGING = 32
I
CCA
vs. DOUT LOAD
DS3234 toc05
CAPACITANCE (pF)
SUPPLY CURRENT (μA)
40
30
20
10
250
350
300
400
450
500
200
0
SCLK = 4MHz
DELTA TIME AND FREQUENCY
vs. TEMPERATURE
TEMPERATURE (°C)
DELTA FREQUENCY (ppm)
DELTA TIME (MIN/YEAR)
807050 60-10 0 10 20 30 40-30 -20
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
20
-200
-80
-60
-40
-20
0
-100
-40
DS3234 toc06
CRYSTAL
+20ppm
CRYSTAL
-20ppm
TYPICAL CRYSTAL,
UNCOMPENSATED
DS3234
ACCURACY
BAND
Typical Operating Characteristics
(VCC= +3.3V, TA = +25°C, unless otherwise noted.)
DS3234
Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Maxim Integrated | 8www.maximintegrated.com
Pin Description
Pin Configuration
TOP VIEW
N.C.
32kHz
INT/SQW
RST
N.C.
N.C.
CS
1
2
3
4
CC
DS3234
5
6
7
8
9
10
20
SCLK
19
DOUT
18
SCLK
17
DINV
V
16
BAT
15
GND
14
N.C.
13
N.C.N.C.
12
N.C.
11
N.C.N.C.
SO
PIN NAME FUNCTION
1 CS Active-Low Chip Select Input. Used to select or deselect the device.
2, 7–14 N.C. No Connection. Not connected internally. Must be connected to ground.
3 32kHz
4VCCDC Power Pin for Primary Power Supply. This pin should be decoupled using a 0.1µF to 1.0µF capacitor.
5 INT/SQW
32kHz Push-Pull Output. If disabled with either EN32kHz = 0 or BB32kHz = 0, the state of the 32kHz pin will be
low.
Active-Low Interrupt or Square-Wave Output. This open-drain pin requires an external pullup resistor. It can be
left open if not used. This multifunction pin is determined by the state of the INTCN bit in the Control Register
(0Eh). When INTCN is set to logic 0, this pin outputs a square wave and its frequency is determined by RS2
and RS1 bits. When INTCN is set to logic 1, then a match between the timekeeping registers and either of the
alarm registers activates the INT/SQW pin (if the alarm is enabled). Because the INTCN bit is set to logic 1
when power is first applied, the pin defaults to an interrupt output with alarms disabled. The pullup voltage can
be up to 5.5V, regardless of the voltage on V
. If not used, this pin can be left unconnected.
CC
Active-Low Reset. This pin is an open-drain input/output. It indicates the status of V
specification. As VCC falls below VPF, the RST pin is driven low. When VCC exceeds VPF, for t
V
PF
6 RST
pin is driven high impedance. The active-low, open-drain output is combined with a debounced pushbutton
input function. This pin can be activated by a pushbutton reset request. It has an internal 50k_ nominal value
pullup resistor to V
oscillator is disabled, t
15 GND Ground
Backup Power-Supply Input. If V
16 V
pin and the battery can cause improper operation. UL recognized to ensure against reverse charging when
BAT
used with a lithium battery. Go to
17 DIN SPI Data Input. Used to shift address and data into the device.
SPI Clock Input. Used to control timing of data into and out of the device. Either clock polarity can be used. The
18, 20 SCLK
clock polarity is determined by the device based on the state of SCLK when CS goes low. Pins 18 and 20 are
electrically connected together internally.
19 DOUT SPI Data Output. Data is output on this pin when the device is in read mode; CMOS push-pull driver.
relative to the
CC
RST
. No external pullup resistors should be connected. On first power-up, or if the crystal
CC
is bypassed and RST immediately goes high.
RST
is not used, connect to ground. Diodes placed in series between the V
BAT
www.maximintegrated.com/qa/info/ul.
, the RST
BAT
DS3234
Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Maxim Integrated | 9www.maximintegrated.com
Block Diagram
Detailed Description
The DS3234 is a TCXO and RTC with integrated crystal
and 256 bytes of SRAM. An integrated sensor periodically samples the temperature and adjusts the oscillator load to compensate for crystal drift caused by
temperature variations. The DS3234 provides userselectable sample rates. This allows the user to select
a temperature sensor sample rate that allows for various temperature rates of change, while minimizing current consumption by temperature sensor sampling. The
user should select a sample rate based upon the
expected temperature rate of change, with faster sample rates for applications where the ambient temperature changes significantly over a short time. The TCXO
provides a stable and accurate reference clock, and
maintains the RTC to within ±2 minutes per year accuracy from -40°C to +85°C. The TCXO frequency output
is available at the 32kHz pin. The RTC is a low-power
clock/calendar with two programmable time-of-day
alarms and a programmable square-wave output. The
INT/SQW provides either an interrupt signal due to
alarm conditions or a square-wave output. The
clock/calendar provides seconds, minutes, hours, day,
X1
X2
OSCILLATOR AND
CAPACITOR ARRAY
CONTROL LOGIC/
DIVIDER
32kHz
INT/SQW
SQUARE-WAVE BUFFER;
INT/SQW CONTROL
N
V
CC
DS3234
V
CC
V
BAT
GND
SCLK
SCLK
DIN
DOUT
POWER CONTROL
CS
SPI INTERFACE AND
ADDRESS REGISTER
DECODE
TEMPERATURE
SENSOR
VOLTAGE REFERENCE;
DEBOUNCE CIRCUIT;
PUSHBUTTON RESET
CONTROL AND STATUS
REGISTERS
SRAM
CLOCK AND CALENDAR
REGISTERS
USER BUFFER
(7 BYTES)
N
RST
DS3234
Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Maxim Integrated | 10www.maximintegrated.com
date, month, and year information. The date at the end
of the month is automatically adjusted for months with
fewer than 31 days, including corrections for leap year.
The clock operates in either the 24-hour or 12-hour format with AM/PM indicator. Access to the internal registers is possible through an SPI bus interface.
A temperature-compensated voltage reference and
comparator circuit monitors the level of VCCto detect
power failures and to automatically switch to the backup
supply when necessary. When operating from the backup supply, access is inhibited to minimize supply current. Oscillator, time and date, and TCXO operations can
continue while the backup supply powers the device.
The RST pin provides an external pushbutton function
and acts as an indicator of a power-fail event.
Operation
The block diagram shows the main elements of the
DS3234. The eight blocks can be grouped into four
functional groups: TCXO, power control, pushbutton
function, and RTC. Their operations are described separately in the following sections.
32kHz TCXO
The temperature sensor, oscillator, and control logic
form the TCXO. The controller reads the output of the
on-chip temperature sensor and uses a lookup table to
determine the capacitance required, adds the aging
correction in the AGE register, and then sets the
capacitance selection registers. New values, including
changes to the AGE register, are loaded only when a
change in the temperature value occurs. The temperature is read on initial application of VCCand once every
64 seconds (default, see the description for CRATE1
and CRATE0 in the
Control/Status Register
section)
afterwards.
Power Control
The power control function is provided by a temperature-compensated voltage reference and a comparator
circuit that monitors the VCClevel. The device is fully
accessible and data can be written and read when V
CC
is greater than VPF. However, when VCCfalls below
both VPFand V
BAT
, the internal clock registers are
blocked from any access. If VPFis less than V
BAT
, the
device power is switched from VCCto V
BAT
when V
CC
drops below VPF. If VPFis greater than V
BAT
, the
device power is switched from VCCto V
BAT
when V
CC
drops below V
BAT
. After VCCreturns above both V
PF
and V
BAT
, read and write access is allowed after RST
goes high (Table 1).
To preserve the battery, the first time V
BAT
is applied to
the device, the oscillator does not start up until V
CC
crosses VPF. After the first time VCCis ramped up, the
oscillator starts up and the V
BAT
source powers the
oscillator during power-down and keeps the oscillator
running. When the DS3234 switches to V
BAT
, the oscil-
lator may be disabled by setting the EOSC bit.
V
BAT
Operation
There are several modes of operation that affect the
amount of V
BAT
current that is drawn. When the part is
powered by V
BAT
, timekeeping current (I
BATT
), which
includes the averaged temperature conversion current,
I
BATTC
, is drawn (refer to Application Note 3644:
Power
Considerations for Accurate Real-Time Clocks
for
details). Temperature conversion current, I
BATTC
, is
specified since the system must be able to support the
periodic higher current pulse and still maintain a valid
voltage level. Data retention current, I
BATTDR
, is the
current drawn by the part when the oscillator is
stopped (EOSC = 1). This mode can be used to minimize battery requirements for times when maintaining
time and date information is not necessary, e.g., while
the end system is waiting to be shipped to a customer.
Pushbutton Reset Function
The DS3234 provides for a pushbutton switch to be
connected to the RST output pin. When the DS3234 is
not in a reset cycle, it continuously monitors the RST
signal for a low going edge. If an edge transition is
detected, the DS3234 debounces the switch by pulling
the RST low. After the internal timer has expired
(PBDB), the DS3234 continues to monitor the RST line.
If the line is still low, the DS3234 continuously monitors
the line looking for a rising edge. Upon detecting
release, the DS3234 forces the RST pin low and holds it
low for t
RST
.
The same pin, RST, is used to indicate a power-fail
condition. When VCCis lower than VPF, an internal
power-fail signal is generated, which forces the RST pin
low. When VCCreturns to a level above VPF, the RST
pin is held low for t
REC
to allow the power supply to sta-
bilize. If the EOSC bit is set to logic 1 (to disable the
oscillator in battery-backup mode), t
REC
is bypassed
and RST immediately goes high.
Table 1. Power Control
SUPPLY CONDITION
VCC < VPF, VCC < V
VCC < VPF, VCC > V
VCC > VPF, VCC < V
VCC > VPF, VCC > V
READ/WRITE
BAT
BAT
BAT
BAT
ACCESS
No V
Yes V
Yes V
Yes V
ACTIVE
SUPPLY
BAT
CC
CC
CC
RST
Active
Active
Inactive
Inactive
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When RST is active due to a power-fail condition (see
Table 1), SPI operations are inhibited while the TCXO
and RTC continue to operate. When RST is active due
to a pushbutton event, it does not affect the operation
of the TCXO, SPI interface, or RTC functions.
Real-Time Clock
With the clock source from the TCXO, the RTC provides
seconds, minutes, hours, day, date, month, and year
information. The date at the end of the month is automatically adjusted for months with fewer than 31 days,
including corrections for leap year. The clock operates
in either the 24-hour or 12-hour format with an AM/PM
indicator.
The clock provides two programmable time-of-day
alarms and a programmable square-wave output. The
INT/SQW pin either generates an interrupt due to alarm
condition or outputs a square-wave signal and the
selection is controlled by the bit INTCN.
SRAM
The DS3234 provides 256 bytes of general-purpose
battery-backed read/write memory. The SRAM can be
written or read whenever VCCis above either VPFor
V
BAT
.
Address Map
Figure 1 shows the address map for the DS3234 timekeeping registers. During a multibyte access, when the
address pointer reaches the end of the register space
(13h read, 93h write), it wraps around to the beginning
(00h read, 80h write). The DS3234 does not respond to
a read or write to any reserved address, and the internal address pointer does not increment. Address pointer operation when accessing the 256-byte SRAM data
is covered in the description of the SRAM address and
data registers. On the falling edge of CS, or during a
multibyte access when the address pointer increments
to location 00h, the current time is transferred to a second set of registers. The time information is read from
these secondary registers, while the internal clock registers continue to increment normally. If the time and
date registers are read using a multibyte read, this
eliminates the need to reread the registers in case the
main registers update during a read.
SPI Interface
The DS3234 operates as a slave device on the SPI serial bus. Access is obtained by selecting the part by the
CS pin and clocking data into/out of the part using the
SCLK and DIN/DOUT pins. Multiple byte transfers are
supported within one CS low period. The SPI on the
DS3234 interface is accessible whenever VCCis above
either V
BAT
or VPF.
Clock and Calendar
The time and calendar information is obtained by reading the appropriate register bytes. Figure 1 illustrates
the RTC registers. The time and calendar data are set
or initialized by writing the appropriate register bytes.
The contents of the time and calendar registers are in
binary-coded decimal (BCD) format. The DS3234 can
be run in either 12-hour or 24-hour mode. Bit 6 of the
hours register is defined as the 12- or 24-hour mode
select bit. When high, 12-hour mode is selected. In 12hour mode, bit 5 is the AM/PM bit with logic-high being
PM. In 24-hour mode, bit 5 is the 20-hour bit (20–23
hours). The century bit (bit 7 of the month register) is
toggled when the years register overflows from 99 to
00.
The day-of-week register increments at midnight.
Values that correspond to the day of week are userdefined but must be sequential (i.e., if 1 equals
Sunday, then 2 equals Monday, and so on). Illogical
time and date entries result in undefined operation.
When reading or writing the time and date registers,
secondary (user) buffers are used to prevent errors
when the internal registers update. When reading the
time and date registers, the user buffers are synchronized to the internal registers on the falling edge of CS
or and when the register pointer rolls over to zero. The
time information is read from these secondary registers,
while the clock continues to run. This eliminates the
need to reread the registers in case the main registers
update during a read.
The countdown chain is reset whenever the seconds
register is written. Write transfers occur when the last
bit of a byte is clocked in. Once the countdown chain is
reset, to avoid rollover issues the remaining time and
date registers must be written within 1 second. The 1Hz
square-wave output, if enabled, transitions high 500ms
after the seconds data transfer.
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Figure 1. Address Map for DS3234 Timekeeping Registers and SRAM
Note: Unless otherwise specified, the registers’ state is not defined when power is first applied. Bits defined as 0 cannot be written
to 1 and will always read 0.
ADDRESS
READ/WRITE
00h 80h 0 10 Seconds Seconds Seconds 00–59
01h 81h 0 10 Minutes Minutes Minutes 00–59
02h 82h 0 12/24
03h 83h 0 0 0 0 0 Day Day 1-7
04h 84h 0 0 10 Date Date Date 01-31
05h 85h Century 0 0 10 Mo Month
06h 86h 10 Year Year Year 00-99
07h 87h A1M1 10 Seconds Seconds
08h 88h A1M2 10 Minutes Minutes
09h 89h A1M3 12/24
0Ah 8Ah A1M4 DY/DT
0Bh 8Bh A2M2 10 Minutes Minutes
0Ch 8Ch A2M3 12/24
0Dh 8Dh A2M4 DY/DT
0Eh 8Eh EOSC BBSQW CONV RS2 RS1 INTCN A2IE A1IE Control —
0Fh 8Fh OSF BB32kHz CRATE1 CRATE0 EN32kHz BSY A2F A1F
10h 90h SIGN DATA DATA DATA DATA DATA DATA DATA
11h 91h SIGN DATA DATA DATA DATA DATA DATA DATA Temp MSB Read Only
12h 92h DATA DATA 0 0 0 0 0 0 Temp LSB Read Only
13h 93h 0 0 0 0 0 0 0 BB_TD
14h–17h 94h–97h — — — — — — — — Reserved —
18h 98h A7 A6 A5 A4 A3 A2 A1 A0
19h 99h D7 D6 D5 D4 D3 D2 D1 D0 SRAM Data —
MSB
BIT 7
BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1
AM/PM
20 hr
AM/PM
20 hr
AM/PM
20 hr
10 hr Hour Hours
10 hr Hour Alarm 1 Hours
0
10 Date
10 hr Hour Alarm 2 Hours
0
10 Date
Day
Date
Day
Date
LSB
BIT 0
FUNCTION RANGE
1-12 +AM /PM
Month/
Century
Alarm 1
Seconds
Alarm 1
Minutes
Alarm 1 Day
Alarm 1 Date
Alarm 2
Minutes
Alarm 2 Day
Alarm 2 Date
Control/
Status
Crystal Aging
Offset
Disable Temp
Conversions
SRAM
Address
01-12 +
Century
1-12 +AM /PM
1-12 +AM /PM
00-23
00-59
00-59
00-23
1-7
01-31
00-59
00-23
1-7
01-31
—
—
—
—
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Alarms
The DS3234 contains two time-of-day/date alarms. Alarm
1 can be set by writing to registers 07h to 0Ah. Alarm 2
can be set by writing to registers 0Bh to 0Dh. The alarms
can be programmed (by the alarm enable and INTCN
bits of the control register) to activate the INT/SQW output
on an alarm match condition. Bit 7 of each of the time-ofday/date alarm registers are mask bits (Table 2). When all
the mask bits for each alarm are logic 0, an alarm only
occurs when the values in the timekeeping registers
match the corresponding values stored in the time-ofday/date alarm registers. The alarms can also be programmed to repeat every second, minute, hour, day, or
date. Table 2 shows the possible settings. Configurations
not listed in the table will result in illogical operations.
The DY/DT bits (bit 6 of the alarm day/date registers)
control whether the alarm value stored in bits 0 to 5 of
that register reflects the day of the week or the date of
the month. If DY/DT is written to logic 0, the alarm will
be the result of a match with date of the month. If
DY/DT is written to logic 1, the alarm will be the result of
a match with day of the week.
When the RTC register values match alarm register settings, the corresponding Alarm Flag ‘A1F’ or ‘A2F’ bit is
set to logic 1. If the corresponding Alarm Interrupt
Enable ‘A1IE’ or ‘A2IE’ is also set to logic 1 and the
INTCN bit is set to logic 1, the alarm condition activates
the INT/SQW signal. The match is tested on the onceper-second update of the time and date registers.
Table 2. Alarm Mask Bits
DY/DT
X 1 1 1 1 Alarm once per second
X 1 1 1 0 Alarm when seconds match
X 1 1 0 0 Alarm when minutes and seconds match
X 1 0 0 0 Alarm when hours, minutes, and seconds match
0 0 0 0 0 Alarm when date, hours, minutes, and seconds match
1 0 0 0 0 Alarm when day, hours, minutes, and seconds match
ALARM 1 REGISTER MASK BITS (BIT 7)
A1M4 A1M3 A1M2 A1M1
ALARM RATE
DY/DT
X 1 1 1 Alarm once per minute (00 seconds of every minute)
X 1 1 0 Alarm when minutes match
X 1 0 0 Alarm when hours and minutes match
0 0 0 0 Alarm when date, hours, and minutes match
1 0 0 0 Alarm when day, hours, and minutes match
ALARM 2 REGISTER MASK BITS (BIT 7)
A2M4 A2M3 A2M2
ALARM RATE
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Special-Purpose Registers
The DS3234 has two additional registers (control and
control/status) that control the real-time clock, alarms,
and square-wave output.
Control Register (0Eh/8Eh)
Bit 7: Enable Oscillator (EOSC). When set to logic 0,
the oscillator is started. When set to logic 1, the oscillator is stopped when the DS3234 switches to battery
power. This bit is clear (logic 0) when power is first
applied. When the DS3234 is powered by VCC, the
oscillator is always on regardless of the status of the
EOSC bit. When EOSC is disabled, all register data is
static.
Bit 6: Battery-Backed Square-Wave Enable
(BBSQW). When set to logic 1 with INTCN = 0 and V
CC
< VPF, this bit enables the square wave. When BBSQW
is logic 0, the INT/SQW pin goes high impedance when
VCC< VPF. This bit is disabled (logic 0) when power is
first applied.
Bit 5: Convert Temperature (CONV). Setting this bit to
1 forces the temperature sensor to convert the temperature into digital code and execute the TCXO algorithm
to update the capacitance array to the oscillator. This
can only happen when a conversion is not already in
progress. The user should check the status bit BSY
before forcing the controller to start a new TCXO execution. A user-initiated temperature conversion does
not affect the internal 64-second (default interval)
update cycle. This bit is disabled (logic 0) when power
is first applied.
A user-initiated temperature conversion does not affect
the BSY bit for approximately 2ms. The CONV bit
remains at a 1 from the time it is written until the conversion is finished, at which time both CONV and BSY go
to 0. The CONV bit should be used when monitoring
the status of a user-initiated conversion.
Bits 4 and 3: Rate Select (RS2 and RS1). These bits
control the frequency of the square-wave output when
the square wave has been enabled. The following table
shows the square-wave frequencies that can be selected with the RS bits. These bits are both set to logic 1
(8.192kHz) when power is first applied.
Bit 2: Interrupt Control (INTCN). This bit controls the
INT/SQW signal. When the INTCN bit is set to logic 0, a
square wave is output on the INT/SQW pin. When the
INTCN bit is set to logic 1, a match between the timekeeping registers and either of the alarm registers activates the INT/SQW (if the alarm is also enabled). The
corresponding alarm flag is always set regardless of
the state of the INTCN bit. The INTCN bit is set to logic
1 when power is first applied.
Bit 1: Alarm 2 Interrupt Enable (A2IE). When set to
logic 1, this bit permits the alarm 2 flag (A2F) bit in the
status register to assert INT/SQW (when INTCN = 1).
When the A2IE bit is set to logic 0 or INTCN is set to
logic 0, the A2F bit does not initiate an interrupt signal.
The A2IE bit is disabled (logic 0) when power is first
applied.
Bit 0: Alarm 1 Interrupt Enable (A1IE). When set to
logic 1, this bit permits the alarm 1 flag (A1F) bit in the
status register to assert INT/SQW (when INTCN = 1).
When the A1IE bit is set to logic 0 or INTCN is set to
logic 0, the A1F bit does not initiate the INT/SQW signal. The A1IE bit is disabled (logic 0) when power is
first applied.
SQUARE-WAVE OUTPUT FREQUENCY
Control Register (0Eh/8Eh)
*
POR is defined as the first application of power to the device, either V
BAT
or VCC.
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
NAME:
POR*:
EOSC BBSQW CONV RS2 RS1 INTCN A2IE A1IE
00011100
RS2RS1
0 0 1Hz
0 1 1.024kHz
1 0 4.096kHz
1 1 8.192kHz
SQUARE-WAVE OUTPUT
FREQUENCY
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Control/Status Register (0Fh/8Fh)
Bit 7: Oscillator Stop Flag (OSF). A logic 1 in this bit
indicates that the oscillator either is stopped or was
stopped for some period and may be used to judge the
validity of the timekeeping data. This bit is set to logic 1
any time that the oscillator stops. The following are
examples of conditions that can cause the OSF bit to
be set:
1) The first time power is applied.
2) The voltages present on both VCCand V
BAT
are
insufficient to support oscillation.
3) The EOSC bit is turned off in battery-backed mode.
4) External influences on the crystal (i.e., noise, leakage, etc.).
This bit remains at logic 1 until written to logic 0.
Bit 6: Battery-Backed 32kHz Output (BB32kHz). This
bit enables the 32kHz output when powered from V
BAT
(provided EN32kHz is enabled). If BB32kHz = 0, the
32kHz output is low when the part is powered by V
BAT
.
This bit is enabled (logic 1) when power is first applied.
Bits 5 and 4: Conversion Rate (CRATE1 and
CRATE0). These two bits control the sample rate of the
TCXO. The sample rate determines how often the temperature sensor makes a conversion and applies compensation to the oscillator. Decreasing the sample rate
decreases the overall power consumption by decreasing the frequency at which the temperature sensor
operates. However, significant temperature changes
that occur between samples may not be completely
compensated for, which reduce overall accuracy.
These bits are set to logic 0 when power is first applied.
Bit 3: Enable 32kHz Output (EN32kHz). This bit indicates the status of the 32kHz pin. When set to logic 1,
the 32kHz pin is enabled and outputs a 32.768kHz
square-wave signal. When set to logic 0, the 32kHz pin is
low. The initial power-up state of this bit is logic 1, and a
32.768kHz square-wave signal appears at the 32kHz pin
after a power source is applied to the DS3234. This bit is
enabled (logic 1) when power is first applied.
Bit 2: Busy (BSY). This bit indicates the device is busy
executing TCXO functions. It goes to logic 1 when the
conversion signal to the temperature sensor is asserted
and then is cleared when the conversion is complete.
Bit 1: Alarm 2 Flag (A2F). A logic 1 in the alarm 2 flag
bit indicates that the time matched the alarm 2 registers. If the A2IE bit and INTCN bit are set to logic 1, the
INT/SQW pin is driven low while A2F is active. A2F is
cleared when written to logic 0. This bit can only be
written to logic 0. Attempting to write to logic 1 leaves
the value unchanged.
Bit 0: Alarm 1 Flag (A1F). A logic 1 in the alarm 1 flag
bit indicates that the time matched the alarm 1 registers. If the A1IE bit and the INTCN bit are set to logic 1,
the INT/SQW pin is driven low while A1F is active. A1F
is cleared when written to logic 0. This bit can only be
written to logic 0. Attempting to write to logic 1 leaves
the value unchanged.
Control/Status Register (0Fh/8Fh)
*
POR is defined as the first application of power to the device, either V
BAT
or VCC.
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
NAME:
POR*:
OSF BB32kHz CRATE1 CRATE0 EN32kHz BSY A2F A1F
1 1 0 0 1 0 0 0
CRATE1 CRATE0
00 64
0 1 128
1 0 256
1 1 512
SAMPLE RATE
(seconds)
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Aging Offset Register (10h/90h)
The aging offset register takes a user-provided value to
add to or subtract from the oscillator capacitor array.
The data is encoded in two’s complement, with bit 7
representing the SIGN bit. One LSB represents the
smallest capacitor to be switched in or out of the
capacitance array at the crystal pins. The aging offset
register capacitance value is added or subtracted from
the capacitance value that the device calculates for
each temperature compensation. The offset register is
added to the capacitance array during a normal temperature conversion, if the temperature changes from
the previous conversion, or during a manual user conversion (setting the CONV bit). To see the effects of the
aging register on the 32kHz output frequency immediately, a manual conversion should be performed after
each aging offset register change.
Positive aging values add capacitance to the array,
slowing the oscillator frequency. Negative values
remove capacitance from the array, increasing the
oscillator frequency.
The change in ppm per LSB is different at different temperatures. The frequency vs. temperature curve is shifted by the values used in this register. At +25°C, one
LSB typically provides about 0.1ppm change in fre-
quency. These bits are all set to logic 0 when power is
first applied.
Use of the aging register is not needed to achieve the
accuracy as defined in the EC tables, but could be
used to help compensate for aging at a given temperature. See the
Typical Operating Characteristics
section
for a graph showing the effect of the register on accuracy over temperature.
Temperature Registers (11h–12h)
Temperature is represented as a 10-bit code with a resolution of 0.25°C and is accessible at location 11h and
12h. The temperature is encoded in two’s complement
format, with bit 7 in the MSB representing the SIGN bit.
The upper 8 bits, the integer portion, are at location 11h
and the lower 2 bits, the fractional portion, are in the
upper nibble at location 12h. Example: 00011001 01b =
+25.25°C. Upon power reset, the registers are set to a
default temperature of 0°C and the controller starts a
temperature conversion.
The temperature is read on initial application of V
CC
and once every 64 seconds afterwards. The temperature registers are updated after each user-initiated conversion and on every 64-second conversion. The
temperature registers are read-only.
Aging Offset (10h/90h)
Temperature Register (MSB) (11h)
Temperature Register (LSB) (12h)
*
POR is defined as the first application of power to the device, either V
BAT
or VCC.
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
NAME:
POR*:
NAME:
POR*:
NAME:
POR*:
SIGN DATA DATA DATA DATA DATA DATA DATA
00000000
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
SIGN DATA DATA DATA DATA DATA DATA DATA
00000000
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
DATA DATA 0 0 0 0 0 0
00000000
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Temperature Control Register
(13h/93h)
Bit 0: Battery-Backed Temperature Conversion
Disable (BB_TD). The battery-backed tempconv dis-
able bit prevents automatic temperature conversions
when the device is powered by the V
BAT
supply. This
reduces the battery current at the expense of frequency accuracy.
SRAM Address Register (18h/98h)
The SRAM address register provides the 8-bit address
of the 256-byte memory array. The desired memory
address should be written to this register before the
data register is accessed. The contents of this register
are incremented automatically if the data register is
accessed more than once during a single transfer.
When the contents of the address register reach 0FFh,
the next access causes the register to roll over to 00h.
SRAM Data Register (19h/99h)
The SRAM data register provides the data to be written
to or the data read from the 256-byte memory array.
During a read cycle, the data in this register is that
found in the memory location in the SRAM address register (18h/98h). During a write cycle, the data in this register is placed in the memory location in the SRAM
address register (18h/98h). When the SRAM data register is read or written, the internal register pointer
remains at 19h/99h and the SRAM address register
increments after each byte that is read or written, allowing multibyte transfers.
SPI Serial Data Bus
The DS3234 provides a 4-wire SPI serial data bus to communicate in systems with an SPI host controller. The
DS3234 supports both single byte and multiple byte data
transfers for maximum flexibility. The DIN and DOUT pins
are the serial data input and output pins, respectively.
The CS input is used to initiate and terminate a data
transfer. The SCLK pin is used to synchronize data movement between the master (microcontroller) and the slave
devices (see Table 3). The shift clock (SCLK), which is
generated by the microcontroller, is active only during
address and data transfer to any device on the SPI bus.
Input data (DIN) is latched on the internal strobe edge
and output data (DOUT) is shifted out on the shift edge
(Figure 2). There is one clock for each bit transferred.
Address and data bits are transferred in groups of eight.
Temperature Control (13h/93h)
SRAM Address (18h/98h)
SRAM Data (19h/99h)
Figure 2. Serial Clock as a Function of Microcontroller ClockPolarity Bit
Note: These registers do not default to any specific value.
*POR is defined as the first application of power to the device, either V
BAT
or VCC.
NAME:
POR*:
BIT 7
0
0
BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0 0 0 0 0 0 BB_TD
0000000
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
NAME:
A7 A6 A5 A4 A2 A1 A1 A0
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
NAME:
D7 D6 D5 D4 D2 D1 D1 D0
CS
DATA LATCH (WRITE/INTERNAL STROBE)
DATA LATCH (WRITE/INTERNAL STROBE)
NOTE 1: CPHA BIT POLARITY (IF APPLICABLE) MAY NEED TO BE SET ACCORDINGLY.
NOTE 2: CPOL IS A BIT SET IN THE MICROCONTROLLER'S CONTROL REGISTER.
NOTE 3: DOUT REMAINS AT HIGH IMPEDANCE UNTIL 8 BITS OF DATA ARE READY TO BE
SHIFTED OUT DURING A READ.
SHIFT DATA OUT (READ)
SCLK WHEN CPOL = 0
SHIFT DATA OUT (READ)
SCLK WHEN CPOL = 1
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Address and data bytes are shifted MSB first into the
serial data input (DIN) and out of the serial data output
(DOUT). Any transfer requires the address of the byte
to specify a write or read, followed by one or more
bytes of data. Data is transferred out of the DOUT pin
for a read operation and into the DIN for a write operation (Figures 3 and 4).
The address byte is always the first byte entered after
CS is driven low. The most significant bit of this byte
determines if a read or write takes place. If the MSB is
0, one or more read cycles occur. If the MSB is 1, one
or more write cycles occur.
Table 3. SPI Pin Function
Figure 3. SPI Single-Byte Write
Figure 4. SPI Single-Byte Read
*
CPOL is the clock-polarity bit set in the control register of the host microprocessor.
**
DOUT remains at high impedance until 8 bits of data are ready to be shifted out during a read.
MODE
Disable H
Write L
Read L
Read Invalid Location L Don’t Care
CS
CS
*CPOL = 1, SCLK Rising
CPOL = 0, SCLK Falling
CPOL = 1, SCLK Falling
CPOL = 0, SCLK Rising
SCLK DIN DOUT
Input Disabled Input Disabled High Impedance
Data Bit Latch High Impedance
X Next Data Bit Shift**
Don’t Care High Impedance
SCLK
DIN
A6 A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0
R/W
DOUT
HIGH IMPEDANCE
CS
SCLK
DIN
R/W
A6 A5 A4 A3 A2 A1 A0
DOUT
HIGH IMPEDANCE
D7 D6 D5 D4 D3 D2 D1 D0
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Data transfers can occur one byte at a time or in multiple-byte burst mode. After CS is driven low, an address
is written to the DS3234. After the address, one or more
data bytes can be written or read. For a single-byte
transfer, one byte is read or written and then CS is driven high. For a multiple-byte transfer, however, multiple
bytes can be read or written after the address has been
written (Figure 5). Each read or write cycle causes the
RTC register address to automatically increment, which
continues until the device is disabled. The address
wraps to 00h after incrementing to 13h (during a read)
and wraps to 80h after incrementing to 93h (during a
write). An updated copy of the time is loaded into the
user buffers upon the falling edge of CS and each time
the address pointer increments from 13h to 00h.
Because the internal and user copies of the time are
only synchronized on these two events, an alarm condition can occur internally and activate the INT/SQW pin
independently of the user data.
If the SRAM is accessed by reading (address 19h) or
writing (address 99h) the SRAM data register, the contents of the SRAM address register are automatically
incremented after the first access, and all data cycles
will use the SRAM data register.
Handling, PC Board Layout,
and Assembly
The DS3234 package contains a quartz tuning-fork
crystal. Pick-and-place equipment can be used, but
precautions should be taken to ensure that excessive
shock and vibration are avoided. Exposure to reflow is
limited to 2 times maximum. Ultrasonic cleaning should
be avoided to prevent damage to the crystal.
Avoid running signal traces under the package, unless
a ground plane is placed between the package and the
signal line. All N.C. (no connect) pins must be connected to ground.
Figure 5. SPI Multiple-Byte Burst Transfer
CS
SCLK
DIN
WRITE
DIN
READ
DOUT
HIGH IMPEDANCE
ADDRESS
BYTE
ADDRESS
BYTE
DATA BYTE 0 DATA BYTE 1
DATA
BYTE 0
DATA BYTE N
DATA
BYTE 1
DATA
BYTE N
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Chip Information
SUBSTRATE CONNECTED TO GROUND
PROCESS: CMOS
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
20 SO W20#H2
21-0042 90-0108
Package Information
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. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
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licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
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DS3234
Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Revision History
REVISION
NUMBER
0 2/06 Initial release —
1 7/07
2 10/08
3 7/10
REVISION
DATE
DESCRIPTION
Clarified the behavior of t
Description
Corrected the POR for the BB32kHz bit from 0 to 1 15
Updated the Typical Operating Circuit 1
Removed the VPU parameter from the Recommended DC Operating Conditions
table and added verbiage about the pullup to the Pin Description table for
INT/SQW
In the Electrical Characteristics table, added CRATE1 = CRATE0 = 0 to the I
parameter and changed the symbols for Timekeeping Battery Current,
Temperature Conversion Current, and Data-Retention Current from I
to I
I
BATTC
In the AC Electrical Characteristics, changed the t
(max) to 400ns (min)
Added the Delta Time and Frequency vs. Temperature graph in the Typical
Operating Characteristics section
Updated the Block Diagram 9
Added the V
Pushbutton Reset Function, Aging Offset Register (10h/90h), and Temperature
Registers (11h–12h) sections
Corrected the description of when the countdown chain is reset in the Clock and
Calendar section
In the Absolute Maximum Ratings section, added the theta-JA and theta-JC
thermal resistances and Note 1, and changed the soldering temperature to
+260°C; changed the 10-hour bit to 20-hour bit in the Clock and Calendar section
and Table 1; updated the BBSQW bit description in the Control Register
(0Eh/8Eh) section; added the land pattern no. to the Package Information table
, I
BATT
BATTC
Operation section, improved some sections of text for the
BAT
on initial power-up in the RST description of the Pin
REC
, and I
BATTDR
, respectively
specification from 400ns
CWH
, ITC, and
BAT
BATT
PAGES
CHANGED
8
2, 8
3
4
7
10, 16
11
2–5, 8, 11, 12,
14, 20
4 3/15 Updated Benefits and Features section 1
Mouser Electronics
Authorized Distributor
Click to View Pricing, Inventory, Delivery & Lifecycle Information:
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DS3234S# DS3234S#T&R DS3234SN# DS3234SN#T&R
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