DS12B887 Datasheet, PDF (3/16 Pages) Dallas Semiconductor – Real Time Clock

DS12B887
SIGNAL DESCRIPTIONS
GND, V_CC - DC power is provided to the device on these
pins. V_CC is the +5 volt input. When 5 volts are applied
within normal limits, the device is fully accessible and
data can be written and read. When V_CC is below 4.25
volts typical, reads and writes are inhibited. However,
the timekeeping function continues unaffected by the
lower input voltage. As V_CC falls below 3 volts typical,
the RAM and timekeeper are switched over to an inter-
nal lithium energy source. The timekeeping function
maintains an accuracy of ±1 minute per month at 25^oC
regardless of the voltage input on the V_CC pin.
SQW (Square Wave Output) - The SQW pin can output
a signal from one of 13 taps provided by the 15 internal
divider stages of the Real Time Clock. The frequency of
the SQW pin can be changed by programming Register
A as shown in Table 1. The SQW signal can be turned
on and off using the SQWE bit in Register B. The SQW
signal is not available when V_CC is less than 4.25 volts
typical.
PERIODIC INTERRUPT RATE AND SQUARE WAVE OUTPUT FREQUENCY Table 1
SELECT BITS REGISTER A
RS3
RS2
RS1
RS0
t_PI PERIODIC
INTERRUPT RATE
SQW OUTPUT
FREQUENCY
0
0
0
0
None
None
0
0
0
1
3.90625 ms
256 Hz
0
0
1
0
7.8125 ms
128 Hz
0
0
1
1
122.070 ms
8.192 kHz
0
1
0
0
244.141 ms
4.096 kHz
0
1
0
1
488.281 ms
2.048 kHz
0
1
1
0
976.5625 ms
1.024 kHz
0
1
1
1
1.953125 ms
512 Hz
1
0
0
0
3.90625 ms
256 Hz
1
0
0
1
7.8125 ms
128 Hz
1
0
1
0
15.625 ms
64 Hz
1
0
1
1
31.25 ms
32 Hz
1
1
0
0
62.5 ms
16 Hz
1
1
0
1
125 ms
8 Hz
1
1
1
0
250 ms
4 Hz
1
1
1
1
500 ms
2 Hz
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