DESCRIPTION

The DS1305 serial alarm real-time clock provides a full binary coded decimal (BCD) clock calendar that

is accessed by 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 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. In addition, 96 bytes of NV RAM are provided for data storage. The

DS1305 will maintain the time and date, provided the oscillator is enabled, as long as at least one supply

is at a valid level.

An interface logic power-supply input pin (VCCIF) allows the DS1305 to drive SDO and PF pins to a level

that is compatible with the interface logic. This allows an easy interface to 3V 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 that allows a rechargeable energy source (such as a super cap or

rechargeable battery) to be used for a backup supply. The VBAT pin allows the device to be backed up by

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

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-ofday

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

output. Both interrupt outputs operate when the device is powered by VCC1, VCC2, or VBAT.

The DS1305 supports a direct interface to 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.

BENEFITS AND FEATURES

• Completely Manages All Timekeeping

Functions

o Real-Time Clock (RTC) Counts Seconds,

Minutes, Hours, Date of the Month,

Month, Day of the Week, and Year with

Leap-Year Compensation Valid Up to

2100

o 96-Byte, Battery-Backed NV RAM for

Data Storage

o Two Time-Of-Day Alarms,

Programmable on Combination of

Seconds, Minutes, Hours, and Day of the

Week

• Standard Serial Port Interfaces with Most

Microcontrollers

o Supports SPI (Serial Peripheral Interface)

Modes 1 and 3 or Standard 3-Wire

Interface

o Burst Mode for Reading/Writing

Successive Addresses in Clock/RAM

• Multiple Power Supply Pins Ease Adding

Battery For Backup

o Dual-Power Supply Pins for Primary and

Backup Power Supplies

o Optional Trickle Charge Output to

Backup Supply

o 2.0V to 5.5V Operation

• 20-Pin TSSOP Minimizes Required Space

• Optional Industrial Temperature Range:

-40°C to +85°C Supports Operation in a

Wide Range of Applications

• Underwriters Laboratory (UL®) Recognized