Datasheet
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
pulse low for t
rec
(see Table 7. Square wave output frequency). This output may be connected to the reset input of
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,
open drain output driver (with I
OL
as specified in Table 13. DC characteristics).
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).
Table 7. Square wave output frequency
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
the F
32K
pin as long as V
CC
≥ 1.3 V, and the oscillator is running (ST bit = '0'). This function is available within one
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
used, the F
32K
pin should be disconnected and allowed to float.
M41T62, M41T64, M41T65
Watchdog output ( WDO - M41T65 only)
DS3840 - Rev 24
page 19/42