DS17285 Maxim, DS17285 Datasheet - Page 15

• Manufacturer Part Number: DS17285
• Description: The DS17285, DS17485, DS17885, DS17287, DS17487, and DS17887 real-time clocks (RTCs) are designed to be successors to the industry-standard DS12885 and DS12887
• Manufacturer: Maxim

Bits 3 to 0: Rate Selector Bits (RS3 to RS0). These
four rate-selection bits select one of the 13 taps on the
15-stage divider or disable the divider output. The tap
selected can be used to generate an output square
wave (SQW pin) and/or a periodic interrupt. The user
can do one of the following:
1) Enable the interrupt with the PIE bit;
Table 4. Periodic Interrupt Rate and Square-Wave Output Frequency
* RS3 to RS0 determine periodic interrupt rates as listed for E32K = 0.
EXT REG B
E32K
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
RS3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
X
SELECT BITS REGISTER A
RS2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
X
____________________________________________________________________
RS1
X
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
RS0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
X
t
PI
2) Enable the SQW output pin with the SQWE or E32k
3) Enable both at the same time and the same rate; or
4) Enable neither.
Table 4 lists the periodic interrupt rates and the square-
wave frequencies that can be chosen with the RS bits.
PERIODIC INTERRUPT
bits;
1.953125ms
976.5625µs
3.90625ms
3.90625ms
122.070µs
244.141µs
488.281µs
7.8125ms
7.8125ms
15.625ms
31.25ms
62.5ms
125ms
250ms
500ms
RATE
None
*
Real-Time Clocks
SQW OUTPUT FREQUENCY
32.768kHz
8.192kHz
4.096kHz
2.048kHz
1.024kHz
256Hz
128Hz
512Hz
256Hz
128Hz
None
64Hz
32Hz
16Hz
8Hz
4Hz
2Hz
15