M41T82 datasheet(41/61 Pages) STMICROELECTRONICS

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M41T82-M41T83

Clock operation

Doc ID 12578 Rev 12

41/61

The oscillator must start and have run for at least 4 seconds before attempting to reset the

OF bit to 0.

The oscillator fail detect circuit funtions during backup mode. If a triggering event occurs to

disrupt the oscillator during a power-down condition, the OF bit will be set accordingly.

3.13

Oscillator fail interrupt enable (M41T83 only)

With the OFIE bit set, the OF bit will cause the IRQ1/FT/OUT output to be asserted (see

Section 3.14.1 and 3.14.2 for additional conditions that apply). The IRQ1/FT/OUT output is

cleared by resetting the OF bit to 0 (NOT by reading the flags register). Clearing the OFIE bit

will also cause the IRQ1/FT/OUT output to de-assert, but if OFIE is subsequently set prior to

clearing OF, the IRQ1/FT/OUT output will assert immediately upon setting OFIE. Clearing

the OF bit is necessary to prevent such an inadvertent interrupt.

If the alarm in backup enable bit, ABE, is set (along with OFIE), the oscillator fail detect will

cause an interrupt in the IRQ1/FT/OUT pin during backup mode. For additional information

on this, refer to Section 3.14.2.

3.14

IRQ1/FT/OUT pin, frequency test, interrupts and the OUT bit

(M41T83 only)

Four interrupt sources, the frequency test function, and the discrete output bit OUT all share

the IRQ1/FT/OUT pin. Priority is built into the part such that some functions dominate

others. Additionally, the priority depends on configuration bits such as OUT and ABE, and

on whether the part is operating on VCC or is in the backup mode. This pin is an open drain

output and requires an external pull-up resistor.

Figure 23 shows the various signal sources and controlling bits for the IRQ1/FT/OUT output

pin.

Figure 23.

IRQ1/FT/OUT output pin circuit

TIMER

OFIE

AI1E

WDOG

PRE

reload

AF1

WDF

OUT

A1IE

OFIE

TIE

w-dog running

ABE

IRQ1/OUT/FT

Write OF to 0

to clear

Read FLAGS register

to clear

Write watchdog register

to clear

IRQ1/OUT/FT

LOGIC

TI/TP

TIE

AM03013v1

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