m41t66 STMicroelectronics, m41t66 Datasheet - Page 20

• Manufacturer Part Number: m41t66
• Description: Real-time Clocks
• Manufacturer: STMicroelectronics

Clock operation
3.5
Note:
3.6
20/33
Square wave output
The M41T66 offers the user a programmable square wave function which is output on the
SQW pin. RS3-RS0 bits located in 04h establish the square wave output frequency. These
frequencies are listed in
completed, the SQW pin can be turned on and off under software control with the square
wave enable bit (SQWE) located in register 0Ah.
The SQW output is an open drain output driver. The initial power-up default for the SQW
output is 32 KHz.
When the SQW is enabled and the ST bit is set (ST = 1), the square wave output could be
low or high and could drain current through the pull-up resistor.
Due to the output buffer circuitry used for the SQW output, this pin must not be taken to a
voltage greater than V
backup. A low threshold BAT42 diode is recommended (see
Table 4.
Century bits
These two bits will increment in a binary fashion at the turn of the century, and handle all
leap years correctly. See
RS3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
Square wave output frequency
RS2
Square wave bits
CC
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
Table
. A diode is required on the SQW pin for SuperCap™ (or battery)
Table 6 on page 22
4. Once the selection of the SQW frequency has been
RS1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
for additional explanation.
RS0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Figure 4 on page
Frequency
32.768
8.192
4.096
2.048
1.024
None
512
256
128
64
32
16
8
4
2
1
Square wave
7).
Units
kHz
kHz
kHz
kHz
kHz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
M41T66
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