M41T81

Clock operation

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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.

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

0000

None

-

0001

32.768

kHz

0010

8.192

kHz

0011

4.096

kHz

0100

2.048

kHz

0101

1.024

kHz

0110

512

Hz

0111

256

Hz

1000

128

Hz

1001

64

Hz

1010

32

Hz

1011

16

Hz

11008

Hz

11014

Hz

11102

Hz

11111

Hz