M41T00AUD M41T00AUD clock operation
Doc ID 13480 Rev 5 21/42
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 V
CC
, 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 V
BACK
, the priorities are different. The interrupt
and frequency test functions are disabled, and only the discrete output function can be
used.
When operating from V
CC
, 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 512 Hz 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 V
BACK
, 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
Register bits
IRQ/FT/OUT pin
OFIE FT OUT
On V
CC
1X X OF
0 1 X 512 Hertz
00 1 1
00 0 0
On V
BACK
XX 1 1
XX 0 0
