DALLAS DS1307

DS1307/DS1308
64 X 8 Serial Real Time Clock
www.dalsemi.com
FEATURES
PIN ASSIGNMENT
Real time clock counts seconds, minutes,
hours, date of the month, month, day of the
week, and year with leap year compensation
valid up to 2100
56 byte nonvolatile RAM for data storage
2-wire serial interface
Programmable squarewave output signal
Automatic power-fail detect and switch
circuitry
Consumes less than 500 nA in battery backup
mode with oscillator running
Optional industrial temperature range
-40°C to +85°C (IND) available for DS1307
and DS1308
DS1307 available in 8-pin DIP or SOIC
DS1308 available in 36-pin SMD BGA (Ball
Grid Array)
DS1308 accuracy is better than ±2
minute/month at 25°C
Recognized by Underwriters Laboratory
8
VCC
2
7
SQW/OUT
3
6
SCL
GND
4
5
SDA
X1
l
8
VCC
X2
VBAT
2
7
SQW/OUT
3
6
SCL
GND
4
5
SDA
DS1307Z 8-Pin SOIC (150 mil)
A B
GND
VBAT
GND
SCL
GND
8-Pin DIP
8-Pin SOIC (150 mil)
8-Pin DIP (Industrial)
8-Pin SOIC (Industrial)
36-Pin BGA
36-Pin BGA (Industrial)
l
X2
VBAT
DS1307 8-Pin DIP (300 mil)
ORDERING INFORMATION
DS1307
DS1307Z
DS1307N
DS1307ZN
DS1308
DS1308N
X1
C D
1
2
3
4
5
6
7
8
9
GND
VCC
SQW/
OUT
GND
SDA
GND
DS1308 36-Pin SMD BGA
(Top View)
PIN DESCRIPTION DS1307/DS1308
VCC
X1, X2
VBAT
GND
SDA
SCL
SQW/OUT
- Primary Power Supply
- 32.768 kHz Crystal Connection
- +3V Battery Input
- Ground
- Serial Data
- Serial Clock
- Square wave/Output Driver
DS1308 PIN IDENTIFIER
VCC
VBAT
SDA
SCL
SQW/OUT
GND
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- C2, C3, D2, D3
- A4, A5, B4, B5
- C7, C8, D7, D8
- A7, A8, B7, B8
- C4, C5, D4, D5
- All Remaining Balls
070900
DS1307/1308
DESCRIPTION
The DS1307 Serial Real Time Clock is a low power, full BCD clock/calendar plus 56 bytes of
nonvolatile SRAM. Address and data are transferred serially via a 2-wire bi-directional bus. The
clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The end of the
month date is automatically adjusted for months with less than 31 days, including corrections for leap
year. The clock operates in either the 24-hour or 12-hour format with AM/PM indicator. The DS1307
has a built-in power sense circuit which detects power failures and automatically switches to the battery
supply.
The DS1308 incorporates the DS1307 chip with a 32.768 kHz crystal in a surface mountable, 36-pin ball
grid array package (BGA). The close proximity of the embedded crystal to the high impedance crystal
input pins on the DS1307 minimizes capacitive loading and noise injection problems associated with
many other oscillator designs. The total area required for installation is less than that of one United States
dime: thus, minimizing PCB space required.
OPERATION
The DS1307/1308 operates as a slave device on the serial bus. Access is obtained by implementing a
START condition and providing a device identification code followed by a register address. Subsequent
registers can be accessed sequentially until a STOP condition is executed. When VCC falls below 1.25 x
VBAT the device terminates an access in progress and resets the device address counter. Inputs to the
device will not be recognized at this time to prevent erroneous data from being written to the device from
an out of tolerance system. When VCC falls below VBAT the device switches into a low current battery
backup mode. Upon power up, the device switches from battery to VCC when VCC is greater than VBAT
+0.2V and recognizes inputs when VCC is greater than 1.25 x VBAT. The block diagram in Figure 1 shows
the main elements of the Serial Real Time Clock.
DS1307/DS1308 BLOCK DIAGRAM Figure 1
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DS1307/1308
SIGNAL DESCRIPTIONS
VCC, GND - DC power is provided to the device on these pins. VCC is the +5 volt input. When 5 volts is
applied within normal limits, the device is fully accessible and data can be written and read. When a
3-volt battery is connected to the device and VCC is below 1.25 x VBAT, reads and writes are inhibited.
However, the Timekeeping function continues unaffected by the lower input voltage. As VCC falls below
VBAT the RAM and timekeeper are switched over to the external power supply (nominal 3.0V DC) at
VBAT.
VBAT - Battery input for any standard 3-volt lithium cell or other energy source. Battery voltage must be
held between 2.0 and 3.5 volts for proper operation. The nominal write protect trip point voltage at which
access to the real time clock and user RAM is denied is set by the internal circuitry as 1.25 x VBAT
nominal. A lithium battery with 48 mAhr or greater will back up the DS1307/DS1308 for more than 10
years in the absence of power at 25 degrees C.
SCL (Serial Clock Input) - SCL is used to synchronize data movement on the serial interface.
SDA (Serial Data Input/Output) - SDA is the input/output pin for the 2-wire serial interface. The SDA
pin is open drain which requires an external pullup resistor.
SQW/OUT (Square Wave/ Output Driver) - When enabled, the SQWE bit set to 1, the SQW/OUT pin
outputs one of four square wave frequencies (1 Hz, 4 kHz, 8 kHz, 32 kHz). The SQW/OUT pin is open
drain which requires an external pullup resistor. SQW/OUT will operate with either Vcc or Vbat applied.
NOTE: X1, X2 are not applicable for the DS1308 or DS1308N.
X1, X2 - Connections for a standard 32.768 kHz quartz crystal. The internal oscillator circuitry is
designed for operation with a crystal having a specified load capacitance (CL) of 12.5 pF.
For more information on crystal selection and crystal layout considerations, please consult Application
Note 58, “Crystal Considerations with Dallas Real Time Clocks.” The DS1307 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.
Please review Application Note 95, “Interfacing the DS1307/DS1308 with a 8051-Compatible
Microcontroller” for additional information.
RTC AND RAM ADDRESS MAP
The address map for the RTC and RAM registers of the DS1307/DS1308 is shown in Figure 2. The real
time clock registers are located in address locations 00h to 07h. The RAM registers are located in address
locations 08h to 3Fh. During a multi-byte access, when the address pointer reaches 3Fh, the end of RAM
space, it wraps around to location 00h, the beginning of the clock space.
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DS1307/1308
DS1307 ADDRESS MAP Figure 2
00H
SECONDS
MINUTES
HOURS
DAY
DATE
MONTH
YEAR
07H
08H
CONTROL
RAM
56 x 8
3FH
CLOCK AND CALENDAR
The time and calendar information is obtained by reading the appropriate register bytes. The real time
clock registers are illustrated in Figure 3. The time and calendar are set or initialized by writing the
appropriate register bytes. The contents of the time and calendar registers are in the Binary-Coded
Decimal (BCD) format. Bit 7 of Register 0 is the Clock Halt (CH) bit. When this bit is set to a 1, the
oscillator is disabled. When cleared to a 0, the oscillator is enabled.
Please note that the initial power on state of all registers is not defined. Therefore it is important to
enable the oscillator (CH bit=0) during initial configuration.
The DS1307/DS1308 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, the 12-hour mode is selected. In the 12-hour mode, bit
5 is the AM/PM bit with logic high being PM. In the 24-hour mode, bit 5 is the second 10 hour bit (20-23
hours).
On a 2-wire START, the current time is transferred to a second set of registers. The time information is
read from these secondary registers, while the clock may continue to run. This eliminates the need to reread the registers in case of an update of the main registers during a read.
DS1307/DS1308 TIMEKEEPER REGISTERS Figure 3
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DS1307/1308
CONTROL REGISTER
The DS1307/DS1308 Control Register is used to control the operation of the SQW/OUT pin.
BIT 7
OUT
BIT 6
X
BIT 5
X
BIT 4
SQWE
BIT 3
X
BIT 2
X
BIT 1
RS1
BIT 0
RS0
OUT (Output control): This bit controls the output level of the SQW/OUT pin when the square wave
output is disabled. If SQWE=0, the logic level on the SQW/OUT pin is 1 if OUT=1 and is 0 if OUT=0.
SQWE (Square Wave Enable): This bit, when set to a logic 1, will enable the oscillator output. The
frequency of the square wave output depends upon the value of the RS0 and RS1 bits.
RS (Rate Select): These bits control the frequency of the square wave output when the square wave
output has been enabled. Table 1 lists the square wave frequencies that can be selected with the RS bits.
SQUAREWAVE OUTPUT FREQUENCY Table 1
RS1
RS0
0
0
1
1
0
1
0
1
SQW OUTPUT
FREQUENCY
1 Hz
4.096 kHz
8.192 kHz
32.768 kHz
2-WIRE SERIAL DATA BUS
The DS1307 supports a bi-directional 2-wire bus and data transmission protocol. A device that sends
data onto the bus is defined as a transmitter and a device receiving data as a receiver. The device that
controls the message is called a master. The devices that are controlled by the master are referred to as
slaves. The bus must be controlled by a master device which generates the serial clock (SCL), controls
the bus access, and generates the START and STOP conditions. The DS1307/DS1308 operates as a slave
on the 2-wire bus. A typical bus configuration using this 2-wire protocol is show in Figure 4.
TYPICAL 2-WIRE BUS CONFIGURATION Figure 4
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DS1307/1308
Figures 5, 6, and 7 detail how data is transferred on the 2-wire bus.
Data transfer may be initiated only when the bus is not busy.
During data transfer, the data line must remain stable whenever the clock line is HIGH. Changes in
the data line while the clock line is high will be interpreted as control signals.
Accordingly, the following bus conditions have been defined:
Bus not busy: Both data and clock lines remain HIGH.
Start data transfer: A change in the state of the data line, from HIGH to LOW, while the clock is HIGH,
defines a START condition.
Stop data transfer: A change in the state of the data line, from LOW to HIGH, while the clock line is
HIGH, defines the STOP condition.
Data valid: The state of the data line represents valid data when, after a START condition, the data line
is stable for the duration of the HIGH period of the clock signal. The data on the line must be changed
during the LOW period of the clock signal. There is one clock pulse per bit of data.
Each data transfer is initiated with a START condition and terminated with a STOP condition. The
number of data bytes transferred between START and STOP conditions is not limited, and is determined
by the master device. The information is transferred byte-wise and each receiver acknowledges with a
ninth bit. Within the 2-wire bus specifications a regular mode (100 kHz clock rate) and a fast mode
(400 kHz clock rate) are defined. The DS1307/DS1308 operates in the regular mode (100 kHz) only.
Acknowledge: Each receiving device, when addressed, is obliged to generate an acknowledge after the
reception of each byte. The master device must generate an extra clock pulse which is associated with
this acknowledge bit.
A device that acknowledges must pull down the SDA line during the acknowledge clock pulse in such a
way that the SDA line is stable LOW during the HIGH period of the acknowledge related clock pulse. Of
course, setup and hold times must be taken into account. A master must signal an end of data to the slave
by not generating an acknowledge bit on the last byte that has been clocked out of the slave. In this case,
the slave must leave the data line HIGH to enable the master to generate the STOP condition.
DATA TRANSFER ON 2-WIRE SERIAL BUS Figure 5
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DS1307/1308
Depending upon the state of the R/ W bit, two types of data transfer are possible:
1. Data transfer from a master transmitter to a slave receiver. The first byte transmitted by the
master is the slave address. Next follows a number of data bytes. The slave returns an acknowledge
bit after each received byte. Data is transferred with the most significant bit (MSB) first.
2. Data transfer from a slave transmitter to a master receiver. The first byte (the slave address) is
transmitted by the master. The slave then returns an acknowledge bit. This is followed by the slave
transmitting a number of data bytes. The master returns an acknowledge bit after all received bytes
other than the last byte. At the end of the last received byte, a ’not acknowledge’ is returned.
The master device generates all of the serial clock pulses and the START and STOP conditions. A
transfer is ended with a STOP condition or with a repeated START condition. Since a repeated START
condition is also the beginning of the next serial transfer, the bus will not be released. Data is transferred
with the most significant bit (MSB) first.
The DS1307/DS1308 may operate in the following two modes:
1. Slave receiver mode (DS1307/DS1308 write mode): Serial data and clock are received through
SDA and SCL. After each byte is received an acknowledge bit is transmitted. START and STOP
conditions are recognized as the beginning and end of a serial transfer. Address recognition is
performed by hardware after reception of the slave address and *direction bit (See Figure 6). The
address byte is the first byte received after the start condition is generated by the master. The address
byte contains the 7 bit DS1307/DS1308 address, which is 1101000, followed by the *direction bit
(R/ W ) which, for a write, is a 0. After receiving and decoding the address byte the device outputs an
acknowledge on the SDA line. After the DS1307/DS1308 acknowledges the slave address + write
bit, the master transmits a register address to the DS1307/DS1308 This will set the register pointer on
the DS1307/DS1308. The master will then begin transmitting each byte of data with the
DS1307/DS1308 acknowledging each byte received. The master will generate a stop condition to
terminate the data write.
DATA WRITE - SLAVE RECEIVER MODE Figure 6
2. Slave transmitter mode (DS1307/DS1308 read mode): The first byte is received and handled as in
the slave receiver mode. However, in this mode, the *direction bit will indicate that the transfer
direction is reversed. Serial data is transmitted on SDA by the DS1307/DS1308 while the serial clock
is input on SCL. START and STOP conditions are recognized as the beginning and end of a serial
transfer (See Figure 7). The address byte is the first byte received after the start condition is
generated by the master. The address byte contains the 7-bit DS1307/DS1308 address, which is
1101000, followed by the *direction bit (R/ W ) which, for a read, is a 1. After receiving and
decoding the address byte the device inputs an acknowledge on the SDA line. The DS1307/DS1308
then begins to transmit data starting with the register address pointed to by the register pointer. If the
register pointer is not written to before the initiation of a read mode the first address that is read is the
last one stored in the register pointer. The DS1307/DS1308 must receive a Not Acknowledge to end
a read.
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DS1307/1308
DATA READ - SLAVE TRANSMITTER MODE Figure 7
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DS1307/1308
ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground
Operating Temperature
Storage Temperature
Soldering Temperature
-0.5V to +7.0V
0°C to 70°C (-40°C to 85°C for industrial)
-55°C to +125°C
260°C for 10 seconds DIP (See NOTE 12)
See JPC/JEDEC Standard J-STD-020A for
Surface Mount Devices
* This is a stress rating only and functional operation of the device at these or any other conditions above
those indicated in the operation sections of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods of time may affect reliability.
The Dallas Semiconductor DS1307/DS1308 is built to the highest quality standards and manufactured for
long term reliability. All Dallas Semiconductor devices are made using the same quality materials and
manufacturing methods. However, standard versions of the DS1307/DS1308 are not exposed to
environmental stresses, such as burn-in, that some industrial applications require. Products which have
successfully passed through this series of environmental stresses are marked IND or N, denoting their
extended operating temperature and reliability rating. For specific reliability information on this product,
please contact the factory at (972) 371-4448.
RECOMMENDED DC OPERATING CONDITIONS
(0°C to 70°C or -40°C to +85°C)
PARAMETER
Supply Voltage
Logic 1
Logic 0
VBAT Battery Voltage
SYMBOL
VCC
VIH
VIL
VBAT
MIN
4.5
2.2
-0.3
2.0
TYP
5.0
MAX
5.5
VCC+0.3
+0.8
3.5
UNITS
V
V
V
V
NOTES
1
1
1
1
DC ELECTRICAL CHARACTERISTICS
(0°C to 70°C or -40°C to +85°C; VCC =4.5V to 5.5V)
PARAMETER
Input Leakage
I/O Leakage
Logic 0 Output
Active Supply Current
Standby Current
Battery Current (OSC ON);
SQW/OUT OFF
Battery Current (OSC ON);
SQW/OUT ON (32 kHz)
SYMBOL
ILI
ILO
VOL
ICCA
ICCS
IBAT1
IBAT2
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MIN
TYP
300
MAX
1
1
0.4
1.5
200
500
UNITS
µA
µA
V
mA
µA
nA
NOTES
10
11
2
9
3
4
480
800
nA
4
DS1307/1308
AC ELECTRICAL CHARACTERISTICS
(0°C to 70°C or -40°C to +85°C; VCC =4.5V to 5.5V)
PARAMETER
SCL Clock Frequency
Bus Free Time Between a STOP and
START Condition
Hold Time (Repeated) START Condition
LOW Period of SCL Clock
HIGH Period of SCL Clock
Set-up Time for a Repeated START
Condition
Data Hold Time
Data Set-up Time
Rise Time of Both SDA and SCL Signals
Fall Time of Both SDA and SCL Signals
Set-up Time for STOP Condition
Capacitive Load for each Bus Line
I/O Capacitance
Crystal Specified Load Capacitance
SYMBOL
fSCL
tBUF
MIN
0
4.7
tHD:STA
tLOW
tHIGH
tSU:STA
tHD:DAT
tSU:DAT
tR
tF
tSU:STO
CB
CI/O
TYP
MAX
100
UNITS
kHz
µs
NOTES
4.0
4.7
4.0
4.7
µs
µs
µs
µs
5
0
250
µs
ns
ns
ns
µs
pF
pF
pF
6, 7
1000
300
4.7
400
10
12.5
8
NOTES:
1.
All voltages are referenced to ground.
2.
Logic zero voltages are specified at a sink current of 5 mA at VCC=4.5V, VOL=GND for capacitive
loads.
3.
ICCS specified with VCC=5.0V and SDA, SCL=5.0V.
4.
VCC=0V, VBAT=3V.
5.
After this period, the first clock pulse is generated.
6.
A device must internally provide a hold time of at least 300 ns for the SDA signal (referred to the
VIHMIN of the SCL signal) in order to bridge the undefined region of the falling edge of SCL.
7.
The maximum tHD:DAT has only to be met if the device does not stretch the LOW period (tLOW) of the
SCL signal.
8.
CB - total capacitance of one bus line in pF.
9.
ICCA - SCL clocking at max frequency = 100 kHz.
10. SCL only.
11. SDA and SQW/OUT
12. The DS1308 is designed to be subjected to no more than two passes through a solder reflow process
to limit premature crystal aging effects and maintain a reasonable accuracy of ±2 minutes/month at
25 degrees C (worst case).
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DS1307/1308
TIMING DIAGRAM Figure 8
DS1307 64 X 8 SERIAL REAL TIME CLOCK
8-PIN DIP MECHANICAL DIMENSIONS
PKG
DIM
A IN.
MM
B IN.
MM
C IN.
MM
D IN.
MM
E IN.
MM
F IN.
MM
G IN.
MM
H IN.
MM
J IN.
MM
K IN.
MM
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8-PIN
MIN
MAX
0.360
0.400
9.14
10.16
0.240
0.260
6.10
6.60
0.120
0.140
3.05
3.56
0.300
0.325
7.62
8.26
0.015
0.040
0.38
1.02
0.120
0.140
3.04
3.56
0.090
0.110
2.29
2.79
0.320
0.370
8.13
9.40
0.008
0.012
0.20
0.30
0.015
0.021
0.38
0.53
DS1307/1308
DS1307Z 64 X 8 SERIAL REAL TIME CLOCK
8-PIN SOIC (150-MIL) MECHANICAL DIMENSIONS
PKG
DIM
A IN.
MM
B IN.
MM
C IN.
MM
E IN.
MM
F IN.
MM
G IN.
MM
H IN.
MM
J IN.
MM
K IN.
MM
L IN.
MM
phi
8-PIN
(150 MIL)
MIN
MAX
0.188
0.196
4.78
4.98
0.150
0.158
3.81
4.01
0.048
0.062
1.22
1.57
0.004
0.010
0.10
0.25
0.053
0.069
1.35
1.75
0.050 BSC
1.27 BSC
0.230
0.244
5.84
6.20
0.007
0.011
0.18
0.28
0.012
0.020
0.30
0.51
0.016
0.050
0.41
1.27
0°
8°
56-G2008-001
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DS1307/1308
DS1308 MECHANICAL DIMENSIONS
PKG
DIM
A IN.
MM
B IN.
MM
C IN.
MM
D IN.
MM
E IN.
MM
F IN.
MM
G IN.
MM
H IN.
MM
36-PIN
BALL GRID
MIN
MAX
0.395
0.405
0.445
0.455
0.022
0.028
0.047
0.053
0.047
0.053
0.347
0.353
0.170
0.190
0.025
0.030
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DS1307/1308
DS1308 RECOMMENDED LAYOUT LAND PATTERN
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