20.3.3.4.3 Single-Slope PWM Generation

For single-slope Pulse-Width Modulation (PWM) generation, the period (T) is controlled by TCAn.PER, while the values of TCAn.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 TCAn.CNT and TCAn.CMPn registers.

Figure 20-10. Single-Slope Pulse-Width Modulation

The TCAn.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, and the TCA prescaler (CLKSEL in TCAn.CTRLA). It is calculated by the following equation where N represents the prescaler divider used:

f PWM_SS = f CLK_PER N ( PER + 1 )