DS1338 I

7 of 16

PIN DESCRIPTION

PIN

8

16

NAME

FUNCTION

1

—

X1

2

—

X2

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

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

Backup Supply Input for Lithium Cell or Other Energy Source. Battery voltage

must be held between the minimum and maximum limits for proper operation.

grounded. UL recognized to ensure against reverse charging when used with a

lithium cell. For more information, visit www.maxim-ic.com/qa/info/ul.

4

15

GND

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

However, the timekeeping function continues unaffected by the lower input

voltage.

5

16

SDA

Serial Data. Input/output pin for the I

output and requires an external pullup resistor. The pull up voltage may be up

6

1

SCL

Serial Clock. Input pin for the I

movement on the serial interface. The pull up voltage may be up to 5.5V

7

2

SQW/OUT

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

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

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

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

—

4–13

N.C.

No Connection. 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 I

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