20.3.3.4.3 Single-Slope PWM Generation

For single-slope Pulse Width Modulation (PWM) generation, the period (T) is controlled by TCA.PER, while the values of TCA.CMPn control the duty cycle of the WG output. The figure below shows how the counter counts from BOTTOM to TOP and then restarts from BOTTOM. The waveform generator (WO) output is set at TOP, and cleared on the compare match between the TCA.CNT and TCA.CMPn registers.

Figure 20-10. Single-Slope Pulse Width Modulation

The TCA.PER register defines the PWM resolution. The minimum resolution is 2 bits (TCA.PER=0x0003), and the maximum resolution is 16 bits (TCA.PER=MAX).

The following equation calculates the exact resolution for single-slope PWM (RPWM_SS):

R PWM_SS = log PER + 1 log 2

The single-slope PWM frequency (fPWM_SS) depends on the period setting (TCA_PER), the system's peripheral clock frequency fCLK_PER, the TCA prescaler (CLKSEL in TCA.CTRLA). It is calculated by the following equation:

f PWM_SS = f CLK_PER N ( PER + 1 )

where N represents the prescaler divider used.