DS1307_06 Datasheet, PDF (6/15 Pages) Maxim Integrated Products – 64 x 8, Serial, I2C Real-Time Clock

DS1307 64 x 8, Serial, I²C Real-Time Clock
PIN DESCRIPTION
PIN NAME
FUNCTION
Connections for Standard 32.768kHz Quartz Crystal. The internal oscillator circuitry is
1
X1
designed for operation with a crystal having a specified load capacitance (C_L) of 12.5pF.
X1 is the input to the oscillator and can optionally be connected to an external 32.768kHz
oscillator. The output of the internal oscillator, X2, is floated if an external oscillator is
connected to X1.
2
X2
Note: For more information on crystal selection and crystal layout considerations, refer to
Application Note 58: Crystal Considerations with Dallas Real-Time Clocks.
Backup Supply Input for Any Standard 3V Lithium Cell or Other Energy Source. Battery
voltage must be held between the minimum and maximum limits for proper operation.
Diodes in series between the battery and the V_BAT pin may prevent proper operation. If a
backup supply is not required, V_BAT must be grounded. The nominal power-fail trip point
3
V_BAT ^(VPF^{) voltage at which access to the RTC and user RAM is denied is set by the internal}
circuitry as 1.25 x V_BAT nominal. A lithium battery with 48mAhr or greater will back up
the DS1307 for more than 10 years in the absence of power at +25°C.
UL recognized to ensure against reverse charging current when used with a lithium
battery. Go to: www.maxim-ic.com/qa/info/ul/.
4
GND Ground
5
SDA
Serial Data Input/Output. SDA is the data input/output for the I²C serial interface. The
SDA pin is open drain and requires an external pullup resistor.
6
SCL
Serial Clock Input. SCL is the clock input for the I²C interface and is used to synchronize
data movement on the serial interface.
Square Wave/Output Driver. When enabled, the SQWE bit set to 1, the SQW/OUT pin
7
SWQ/OUT
outputs one of four square-wave frequencies (1Hz, 4kHz, 8kHz, 32kHz). The SQW/OUT
pin is open drain and requires an external pullup resistor. SQW/OUT operates with either
V_CC or V_BAT applied.
Primary Power Supply. When voltage is applied within normal limits, the device is fully
8
V_CC
accessible and data can be written and read. When a backup supply is connected to the
device and V_CC is below V_TP, read and writes are inhibited. However, the timekeeping
function continues unaffected by the lower input voltage.
DETAILED DESCRIPTION
The DS1307 is a low-power clock/calendar with 56 bytes of battery-backed SRAM. The clock/calendar
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 DS1307 operates as a slave device on the I²C 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 V_CC falls below 1.25 x V_BAT, 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 V_CC falls below V_BAT, the device switches into a low-current battery-backup
mode. Upon power-up, the device switches from battery to V_CC when V_CC is greater than V_BAT +0.2V and
recognizes inputs when V_CC is greater than 1.25 x V_BAT. The block diagram in Figure 1 shows the main
elements of the serial RTC.
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