Datasheet

Clock operation M41T81
18/29 Doc ID 7529 Rev 10
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 Tabl e 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.
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.
Table 4. Square wave output frequency
Square wave bits Square wave
RS3 RS2 RS1 RS0 Frequency Units
0000None-
000132.768kHz
00108.192kHz
00114.096kHz
01002.048kHz
01011.024kHz
0110512Hz
0111256Hz
1000128Hz
100164Hz
101032Hz
101116Hz
11008Hz
11014Hz
11102Hz
11111Hz