The compare channels can be used for waveform generation on output port pins.
To make the waveform available on the connected pin, the following requirements must be
fulfilled:
- Choose a waveform generation mode in
the Waveform Generation Operation bit in Waveform register (CTRLA.WAVEGEN).
- Optionally invert the waveform output
by writing the corresponding Waveform Output Invert Enable bit in the Control C
register (CTRLC.INVx).
- Configure the pins with the I/O Pin
Controller. Refer to PORT - I/O Pin Controller for details.
The counter value is continuously compared
with each CCx value. On a comparison match, the Match or Capture Channel x bit in the
Interrupt Flag Status and Clear register (INTFLAG.MCx) will be set on the next zero-to-one
transition of CLK_TC_CNT (see the next figure). An interrupt/and or event can be generated
on comparison match when INTENSET.MCx=1 and/or EVCTRL.MCEOx=1.
There are four waveform configurations for the Waveform Generation Operation
bit group in the Control A register (CTRLA.WAVEGEN) . This will influence how the waveform
is generated and impose restrictions on the top value. The configurations are:
- Normal frequency (NFRQ)
- Match frequency (MFRQ)
- Normal pulse-width modulation
(NPWM)
- Match pulse-width modulation
(MPWM)
When using NPWM or NFRQ configuration, the TOP will be determined by the
counter resolution. In 8-bit counter mode, the Period register (PER) is used as TOP, and
the TOP can be changed by writing to the PER register. In 16- and 32-bit counter mode, TOP
is fixed to the maximum (MAX) value of the counter.