DS1339 I

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DETAILED DESCRIPTION

The DS1339 serial real-time clock (RTC) is a low-power clock/date device with two programmable time-of-day

alarms and a programmable square-wave output. Address and data are transferred serially through an I

The clock/date 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

clock operates in either the 24-hour or 12-hour format with AM/PM indicator. The DS1339 has a built-in power-

sense circuit that detects power failures and automatically switches to the backup supply, maintaining time and

date operation.

OPERATION

The DS1339 operates as a slave device on the serial bus. Access is obtained by implementing a START condition

and providing a device identification code followed by data. Subsequent registers can be accessed sequentially

Figure 3 shows the main elements of the serial real-time clock.

OSCILLATOR CIRCUIT

The DS1339 uses an external 32.768kHz crystal. The oscillator circuit does not require any external resistors or

capacitors to operate. Table 1 specifies several crystal parameters for the external crystal. Figure 4 shows a

functional schematic of the oscillator circuit. The startup time is usually less than 1 second when using a crystal

with the specified characteristics.