DS1307N Просмотр технического описания (PDF) - Dallas Semiconductor -> Maxim Integrated

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DS1307N

64 x 8 Serial Real-Time Clock

Dallas Semiconductor -> Maxim Integrated 

DS1307

SIGNAL DESCRIPTIONS

VCC, GND – DC power is provided to the device on these pins. VCC is the +5V input. When 5V is

applied within normal limits, the device is fully accessible and data can be written and read. When a 3V

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 3V lithium cell or other energy source. Battery voltage must be

held between 2.0V and 3.5V for proper operation. The nominal write protect trip point voltage at which

access to the RTC and user RAM is denied is set by the internal circuitry as 1.25 x VBAT nominal. A

lithium battery with 48mAhr or greater will back up the DS1307 for more than 10 years in the absence of

power at 25ºC. UL recognized to ensure against reverse charging current when used in conjunction with a

lithium battery.

See “Conditions of Acceptability” at http://www.maxim-ic.com/TechSupport/QA/ntrl.htm.

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 (1Hz, 4kHz, 8kHz, 32kHz). The SQW/OUT pin is open

drain and requires an external pull-up resistor. SQW/OUT will operate with either Vcc or Vbat applied.

X1, X2 – Connections for a standard 32.768kHz quartz crystal. The internal oscillator circuitry is

designed for operation with a crystal having a specified load capacitance (CL) of 12.5pF.

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 32.768kHz oscillator. In this configuration, the X1 pin is connected to the external oscillator

signal and the X2 pin is floated.

RECOMMENDED LAYOUT FOR CRYSTAL

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