M48T59 datasheet(13/21 Pages) STMICROELECTRONICS

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M48T59, M48T59Y, M48T59V

Note: User must transition address (or toggle chip

enable) to see Flag bit change.

When the clock information matches the alarm

clock settings based on the match criteria defined

by RPT1-RPT4, AF (Alarm Flag) is set. If AFE

(Alarm Flag Enable) is also set, the alarm condi-

tion activates the IRQ/FT pin. To disable alarm,

write ‘0’ to the Alarm Date register and RPT1-4.

The alarm flag and the IRQ/FT output are cleared

by a read to the Flags register.

The IRQ/FT pin can also be activated in the bat-

tery back-up mode. The IRQ/FT will go low if an

alarm occurs and both ABE (Alarm in Battery

Back-up Mode Enable) and AFE are set. The ABE

and AFE bits are reset during power-up, therefore

an alarm generated during power-up will only set

AF. The user can read the Flag Register at system

boot-up to determine if an alarm was generated

while the M48T59 was in the deselect mode during

power-up. Figure 12 illustrates the back-up mode

alarm timing.

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 eight bit Watchdog Register (Ad-

dress 1FF7h). The five bits (BMB4-BMB0) store a

binary multiplier and the two lower order bits (RB1-

RB0) select the resolution, where 00 = 1/16 sec-

ond, 01 = 1/4 second, 10 = 1 second, and 11 = 4

seconds. The amount of time-out is then deter-

mined to be the multiplication of the five bit multi-

plier value with the resolution. (For example:

writing 00001110 in the Watchdog Register = 3 x 1

or 3 seconds).

Note: Accuracy of timer is within ± the selected

resolution.

If the processor does not reset the timer within the

specified period, the M48T59 sets the WDF

(Watchdog Flag) and generates a watchdog inter-

rupt or a microprocessor reset.

WDF is reset by reading the Flags Register (Ad-

dress 1FFOh).

Figure 12. Back-up Mode Alarm Waveforms

AI03254B

VCC

IRQ/FT

tREC

VPFD (max)

VPFD (min)

ABE, AFE bit in Interrupt Register

AF bit in Flags Register

HIGH-Z

VSO

HIGH-Z

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