DS1338(2004) データシートの表示（PDF） - Maxim Integrated

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DS1338
(Rev.:2004)

I2C RTC with 56-Byte NV RAM

Maxim Integrated 

DS1338 I2C RTC with 56-Byte NV RAM

PIN DESCRIPTION

PIN

8

16

NAME

1

—

X1

2

—

X2

FUNCTION

32.768kHz Crystal Connections. The internal oscillator circuitry is designed for

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

X1 is the input to the oscillator and can optionally be connected to an external

32.768kHz oscillator. The output of the internal oscillator, pin X2, is floated if an

external oscillator is connected to pin X1. An external 32.768kHz oscillator can

also drive the DS1338. In this configuration, the X1 pin is connected to the

external oscillator signal and the X2 pin is floated.

Note: For more information about crystal selection and crystal layout considerations,

refer to Application Note 58: Crystal Considerations with Dallas Real-Time Clocks.

3

14

4

15

5

16

VBAT

GND

SDA

+3V Battery Input. 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. If a backup supply is not required, VBAT

must be grounded. UL recognized to ensure against reverse charging when

used with a lithium battery.

Ground. DC power is provided to the device on these pins. VCC is the primary

power input. 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 VPF, reads and writes are inhibited.

However, the timekeeping function continues unaffected by the lower input

voltage.

Serial Data. Input/output pin for the I2C serial interface. It is open drain and

requires an external pullup resistor.

6

1

SCL

Serial Clock. Used to synchronize data movement on the serial interface

Square-Wave/Output Driver. When enabled and the SQWE bit set to 1, the

7

2

SQW/OUT

SQW/OUT pin outputs one of four square-wave frequencies (1Hz, 4kHz, 8kHz,

32kHz). It is open drain and requires an external pullup resistor. Operates with

either VCC or VBAT applied.

8

3

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

VCC

connected to the device and VCC is below VPF, reads and writes are inhibited.

However, the timekeeping function continues unaffected by the lower input

voltage.

—

4–13

N.C.

No Connect. These pins are not connected internally, but must be grounded for

proper operation.

DETAILED DESCRIPTION

The DS1338 serial RTC is a low-power, full BCD clock/calendar plus 56 bytes of NV SRAM. Address and data are

transferred serially through an I2C interface. 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 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. The DS1338 has a built-in power-sense circuit that detects power failures and automatically switches to

the battery supply.

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