m41t62 STMicroelectronics, m41t62 Datasheet - Page 26

• Manufacturer Part Number: m41t62
• Description: Serial Access Real-time Clock With Alarms
• Manufacturer: STMicroelectronics

Clock operation
3.4
Note:
Note:
3.5
Note:
26/40
Watchdog timer
The watchdog timer can be used to detect an out-of-control microprocessor. The user
programs the watchdog timer by setting the desired amount of time-out into the Watchdog
Register, address 09h.
Bits BMB4-BMB0 store a binary multiplier and the three bits RB2-RB0 select the resolution
where:
000=1/16 second (16Hz);
001=1/4 second (4Hz);
010=1 second (1Hz);
011=4 seconds (1/4Hz); and
100 = 1 minute (1/60Hz).
Invalid combinations (101, 110, and 111) will NOT enable a watchdog time-out. Setting the
BMB4-BMB0 = 0 with any combination of RB2-RB0, other than 000, will result in an
immediate watchdog time-out.
The amount of time-out is then determined to be the multiplication of the five-bit multiplier
value with the resolution. (For example: writing 00001110 in the Watchdog Register = 3*1 or
3 seconds). If the processor does not reset the timer within the specified period, the M41T6x
sets the WDF (Watchdog Flag) and generates an interrupt on the IRQ pin (M41T62), or a
watchdog output pulse (M41T63 and M41T65 only) on the WDO pin. The watchdog timer
can only be reset by having the microprocessor perform a WRITE of the Watchdog Register.
The time-out period then starts over.
Should the watchdog timer time-out, any value may be written to the Watchdog Register in
order to clear the IRQ pin. A value of 00h will disable the watchdog function until it is again
programmed to a new value. A READ of the Flags Register will reset the Watchdog Flag (Bit
D7; Register 0Fh). The watchdog function is automatically disabled upon power-up, and the
Watchdog Register is cleared.
A WRITE to any clock register will restart the watchdog timer.
Watchdog output (WDO - M41T63/65 only)
If the processor does not reset the watchdog timer within the specified period, the Watchdog
Output (WDO) will pulse low for t
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.
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
on page
32).
rec
(see
Table 17 on page
34). This output may be
OL
as specified in
M41T62/63/64/65
Table 14