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 PIN diagram and  DESCRIPTION of DS1307

 

 

 

PIN

NAME

FUNCTION

 

1

X1

Connections for 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. 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.

Note: For more information on crystal selection and crystal layout considerations, refer to Application Note 58: Crystal Considerations with Dallas Real-Time Clocks.

 

2

X2

 

3

VBAT

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 VBAT pin may prevent proper operation. If a backup supply is not required, VBAT must be grounded. The nominal power-fail trip point (VPF) 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 48mAh or greater will back up the DS1307 for more than 10 years in the absence of power at +25C.

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 pull-up resistor. The pull-up voltage can be up to 5.5V regardless of the voltage on VCC.

 

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. The pull-up voltage can be up to 5.5V regardless of the voltage on VCC.

 

7

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 operates with either VCC or VBAT applied. The pull-up voltage can be up to 5.5V regardless of the voltage on VCC. If not used, this pin can be left floating.

 

8

VCC

Primary Power Supply. When voltage is applied within normal limits, the device is fully accessible and data can be written and read. When a backup supply is connected to the device and VCC is below VTP, read and writes are inhibited. However, the timekeeping function continues unaffected by the lower input voltage.