M41T83RM6F datasheet(37/58 Pages) STMICROELECTRONICS

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M41T82 M41T83

Clock operation

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3.7

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

bits RB1-RB0 select the resolution, where 00 = 1/16 second, 01 = 1/4 second, 10 = 1

second, and 11 = 4 seconds. 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 M41T8x sets the WDF (Watchdog Flag) and

generates a watchdog interrupt.

The watchdog timer can 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, a value of 00h needs to be written to the Watchdog

until it is again programmed correctly. 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. If the watchdog function is set, the frequency test function is activated, and the

SQWE bit is '0,' the watchdog function prevails and the frequency test function is denied.

Table 8.

Alarm repeat modes

RPT5

RPT4

RPT3

RPT2

RPT1

Alarm setting

11111

Once per second

11110

Once per minute

11100

Once per hour

11000

Once per day

10000

Once per month

00000

Once per year

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