DS1307 Datasheet, PDF (4/11 Pages) Dallas Semiconductor – 64 X 8 Serial Real Time Clock

DS1307
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
OUT
BIT 6
X
BIT 5
X
BIT 4
SQWE
BIT 3
X
BIT 2
X
BIT 1
RS1
BIT 0
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
0
0
0
1
1
0
1
1
SQW OUTPUT
FREQUENCY
1 Hz
4.096 kHz
8.192 kHz
32.768 kHz
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