M41T00AUD datasheet(21/44 Pages) STMICROELECTRONICS

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M41T00AUD

M41T00AUD clock operation

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5.3

Priority for IRQ/FT/OUT pin

Three functions share pin 5 of the M41T00AUD. The oscillator fail interrupt (IRQ), the

calibration frequency test output (FT) and the discrete logic output (OUT) all use this pin.

In normal operation, when operating from VCC, the interrupt function has priority over the

frequency test function which in turn has priority over the discrete output function.

In the backup mode, when operating from VBACK, the priorities are different. The interrupt

and frequency test functions are disabled, and only the discrete output function can be

used.

When operating from VCC, if the oscillator fail interrupt enable bit is set (OFIE, D4 of register

09h), the pin is an interrupt output which will be asserted anytime the OF bit (D5 of register

09h) goes true. (See Section 5 for more details.)

During calibration, the pin can be used as a frequency test output. When FT is a 1 (and

OFIE a 0), the device will output a 512Hz test signal on this pin. Users can measure this

with a frequency counter and use that result to determine the appropriate calibration register

value.

Otherwise, when OFIE is a 0 and FT is a 0, it becomes the discrete logic OUT pin and

reflects the value of the OUT bit (D7 of register 07h).

When operating from VBACK, the discrete output function can still be used. The

IRQ/FT/OUT pin will reflect the contents of the out bit.

Note:

The IRQ/FT/OUT pin is open drain and requires an external pull-up resistor.

Table 5.

Priority for IRQ/FT/OUT pin

State

IRQ/FT/OUT pin

OFIE

OUT

On V

512 Hertz

On V

BACK

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