Clock operation

M41T81S

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Doc ID 10773 Rev 7

Square wave output

The M41T81S 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.

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

00

00

None

-

00

01

32.768

kHz

0

0

1

0

8.192

kHz

0

0

1

1

4.096

kHz

0

1

0

0

2.048

kHz

0

1

0

1

1.024

kHz

01

10

512

Hz

01

11

256

Hz

10

00

128

Hz

10

01

64

Hz

10

10

32

Hz

10

11

16

Hz

11

008

Hz

11

014

Hz

11

102

Hz

11

111

Hz