27.6.2.6.1 Waveform Output Operations

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:
  1. Choose a waveform generation mode in the Waveform Generation Operation bit in Waveform register (CTRLA.WAVEGEN).
  2. Optionally invert the waveform output by writing the corresponding Waveform Output Invert Enable bit in the Control C register (CTRLC.INVx).
  3. 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.