MC68HC12 Datasheet, PDF (154/478 Pages) Motorola, Inc – The MC68HC912DT128A microcontroller unit (MCU) is a 16-bit device composed of standard on-chip peripherals including a 16-bit central processing unit

I/O Ports with Key Wake-up
11.4 Key Wake-Up Input Filter
The KWU input signals are filtered by a digital filter which is active only
during STOP mode.
The purpose of the filter is to prevent single pulses shorter than a
specified value from waking the part from STOP.
The filter is composed of an internal oscillator and a majority voting logic.
The filter oscillator starts the oscillation by detecting a triggering edge on
an input if the corresponding interrupt enable bit is set.
The majority voting logic takes three samples of an asserted input pin at
each filter oscillator period and if two samples are taken at the triggering
level, the filter recognizes a valid triggering level and sets the
corresponding interrupt flag. In this way the majority voting logic rejects
the short non-triggering state between two incoming triggering pulses.
As the filter is shared with all KWU inputs, the filter considers any pulse
coming from any input pin for which the corresponding interrupt enable
bit is set.
The timing specification is given for a single pulse. The time interval
between the triggering edges of two following pulses should be greater
than the t_KWSP in order to be considered as a single pulse by the filter. If
this time interval is shorter than t_KWSP, the majority voting logic may treat
the two consecutive pulses as a single valid pulse.
The filter is shared by all the KWU pins. Hence any valid triggering level
on any KWU pin is seen by the filter. The timing specification applies to
the input of the filter.
Technical Data
154
I/O Ports with Key Wake-up
MC68HC912DT128A — Rev 4.0
MOTOROLA