DS1307

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The DS1307 can be run in either 12-hour or 24-hour mode. Bit 6 of the hours register is defined as the

12- or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour mode, bit 5 is

the AM/PM bit with logic high being PM. In the 24-hour mode, bit 5 is the second 10 hour bit (20-

23 hours).

On a 2-wire START, the current time is transferred to a second set of registers. The time information is

read from these secondary registers, while the clock may continue to run. This eliminates the need to re-

read the registers in case of an update of the main registers during a read.

DS1307 TIMEKEEPER REGISTERS Figure 3

CONTROL REGISTER

The DS1307 Control Register is used to control the operation of the SQW/OUT pin.

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

OUT

X

X

SQWE

X

X

RS1

RS0

OUT (Output control): This bit controls the output level of the SQW/OUT pin when the square wave

output is disabled. If SQWE=0, the logic level on the SQW/OUT pin is 1 if OUT=1 and is 0 if OUT=0.

SQWE (Square Wave Enable): This bit, when set to a logic 1, will enable the oscillator output. The

frequency of the square wave output depends upon the value of the RS0 and RS1 bits.

RS (Rate Select): These bits control the frequency of the square wave output when the square wave

output has been enabled. Table 1 lists the square wave frequencies that can be selected with the RS bits.

SQUAREWAVE OUTPUT FREQUENCY Table 1

RS1

RS0

SQW OUTPUT

FREQUENCY

00

1 Hz

0

1

4.096 kHz

1

0

8.192 kHz

1

1

32.768 kHz