DS1305

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PIN DESCRIPTION

- Primary Power Supply

- Backup Power Supply

- +3V Battery Input

- Interface Logic Power Supply Input

GND

- Ground

X1, X2

- 32.768 kHz Crystal Connection

INT0

- Interrupt 0 Output

INT1

- Interrupt 1 Output

SDI

- Serial Data In

SDO

- Serial Data Out

CE

- Chip Enable

SCLK

- Serial Clock

SERMODE - Serial Interface Mode

PF

- Power Fail Output

DESCRIPTION

The DS1305 Serial Alarm Real Time Clock provides a full BCD clock calendar which is accessed via a

simple serial 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 less than 31 days,

including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with

AM/PM indicator. In addition 96 bytes of nonvolatile RAM are provided for data storage.

that is compatible with the interface logic. This allows an easy interface to 3-volt logic in mixed supply

systems.

The DS1305 offers dual power supplies as well as a battery input pin. The dual power supplies support a

programmable trickle charge circuit which allows a rechargeable energy source (such as a super cap or

a non-rechargeable battery. The DS1305 is fully operational from 2.0 to 5.5 volts.

Two programmable time of day alarms are provided by the DS1305.

Each alarm can generate an

interrupt on a programmable combination of seconds, minutes, hours and day. “Don’t care” states can be

inserted into one or more fields if it is desired for them to be ignored for the alarm condition. The time of

day alarms can be programmed to assert two different interrupt outputs or to assert one common interrupt

The DS1305 supports a direct interface to Motorola SPI serial data ports or standard 3-wire interface. A

straightforward address and data format is implemented in which data transfers can occur 1 byte at a time

or in multiple-byte burst mode.

OPERATION

The block diagram in Figure 1 shows the main elements of the Serial Alarm RTC.

The following

paragraphs describe the function of each pin.