DS1302SN datasheet(2/14 Pages) DALLAS

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DS1302

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Interfacing the DS1302 with a microprocessor is simplified by using synchronous serial communication.

Only three wires are required to communicate with the clock/RAM: (1) RST (Reset), (2) I/O (Data line),

and (3) SCLK (Serial clock). Data can be transferred to and from the clock/RAM 1 byte at a time or in a

burst of up to 31 bytes. The DS1302 is designed to operate on very low power and retain data and clock

information on less than 1 microwatt.

The DS1302 is the successor to the DS1202. In addition to the basic timekeeping functions of the

DS1202, the DS1302 has the additional features of dual power pins for primary and back–up power

supplies, programmable trickle charger for VCC1, and seven additional bytes of scratchpad memory.

OPERATION

The main elements of the Serial Timekeeper are shown in Figure 1: shift register, control logic, oscillator,

real time clock, and RAM.

DS1302 BLOCK DIAGRAM Figure 1

SIGNAL DESCRIPTIONS

VCC1 – VCC1 provides low power operation in single supply and battery operated systems as well as low

power battery backup. In systems using the trickle charger, the rechargeable energy source is connected

to this pin.

VCC2 – Vcc2 is the primary power supply pin in a dual supply configuration. VCC1 is connected to a

backup source to maintain the time and date in the absence of primary power.

The DS1302 will operate from the larger of VCC1 or VCC2. When VCC2 is greater than VCC1 + 0.2V, VCC2

will power the DS1302. When VCC2 is less than VCC1, VCC1 will power the DS1302.

SCLK (Serial Clock Input) – SCLK is used to synchronize data movement on the serial interface.

I/O (Data Input/Output) – The I/O pin is the bi-directional data pin for the 3-wire interface.

RST (Reset) – The reset signal must be asserted high during a read or a write.

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