M41T81
Clock operation
3.6
Square wave output
The M41T81 offers the user a programmable square wave function which is output on the
SQW pin. RS3-RS0 bits located in 13h establish the square wave output frequency. These
frequencies are listed in Table 4. Once the selection of the SQW frequency has been
completed, the IRQ/FT/OUT/SQW pin can be turned on and off under software control with
the Square Wave Enable Bit (SQWE) located in Register 0Ah.
Table 4.
Square wave output frequency
Square wave bits
Square wave
RS3
RS2
RS1
RS0
Frequency
Units
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
None
32.768
8.192
4.096
2.048
1.024
512
256
128
64
-
kHz
kHz
kHz
kHz
kHz
Hz
Hz
Hz
Hz
32
Hz
16
Hz
8
Hz
4
Hz
2
Hz
1
Hz
3.7
Century bit
Bits D7 and D6 of Clock Register 03h contain the CENTURY ENABLE Bit (CEB) and the
CENTURY Bit (CB). Setting CEB to a '1' will cause CB to toggle, either from a '0' to '1' or
from '1' to '0' at the turn of the century (depending upon its initial state). If CEB is set to a '0,'
CB will not toggle.
19/30
STMICROELECTRONICS [ ST ]
