Clock operation

M41T80

16/27

Doc ID 9074 Rev 5

3.3

Full-time 32 KHz square wave output

The M41T80 offers the user a special 32 KHz square wave function which defaults to output

on the F32K pin (pin 3) as long as VCC is valid, and the oscillator is running (ST bit = '0'). This

function is available within four seconds of initial power-up and can only be disabled by

setting the 32KE bit to '0' or the ST bit to '1.' If not used, the F32K pin should be disconnected

and allowed to float.

Note:

The F32K pin is an open drain which requires an external pull-up resistor.

3.4

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 5.

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