3.5

Watchdog output ( WDO - M41T65 only)

If the processor does not reset the watchdog timer within the specified period, the watchdog output ( WDO ) will

the processor in order to generate a processor reset. After a watchdog time-out occurs, the timer will remain

disabled until such time as a new countdown value is written into the watchdog register.

Note:

The crystal oscillator must be running for the WDO pulse to be available. The WDO output is an N-channel,

3.6

Square wave output (M41T62/64)

The M41T62/64 offers the user a programmable square wave function which is output on the SQW pin. RS3-RS0

bits located in 04h establish the square wave output frequency. These frequencies are listed in Table 7. Square

wave output frequency. Once the selection of the SQW frequency has been completed, the SQW pin can be

turned on and off under software control with the square wave enable bit (SQWE) located in register 0Ah.

The SQW output is an N-channel, open drain output driver for the M41T64, and a full CMOS output driver for the

M41T62. The initial power-up default for the SQW output is 32 kHz (except for M41T64, which defaults disabled).

Square wave bits

Square wave

RS3

RS2

RS1

RS0

Frequency

Units

0

0

0

0

None

–

0

0

0

1

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

0

1

1

0

512

Hz

0

1

1

1

256

Hz

1

0

0

0

128

Hz

1

0

0

1

64

Hz

1

0

1

0

32

Hz

1

0

1

1

16

Hz

1

1

0

0

8

Hz

1

1

0

1

4

Hz

1

1

1

0

2

Hz

1

1

1

1

1

Hz

3.7

Full-time 32 kHz square wave output (M41T64)

The M41T64 offers the user a special 32 kHz square wave function which is enabled on power-up to output on

second (typ) of initial power-up and can only be disabled by setting the 32KE bit to '0' or the ST bit to '1.' If not

M41T62, M41T64, M41T65

Watchdog output (

WDO

- M41T65 only)

DS3840 - Rev 24

page 19/42