Rainbow Electronics ATmega64C1 - Manual (Page 137)

137
7647A–AVR–02/08
ATmega32/64/M1/C1
Figure 14-3. Cycle Presentation in Centered Mode
Figure 14-2 and Figure 14-3 graphically illustrate the values held in the PSC counter. Centered
Mode is like One Ramp Mode which counts down and then up.
Notice that the update of the waveform generator registers is done regardless of ramp Mode at
the end of the PSC cycle.
14.5.3 Operation Mode Descriptions
Waveforms and duration of output signals are determined by parameters held in the registers
(POCRnSA, POCRnRA, POCRnSB, POCR_RB) and by the running mode. Two modes are pos-
sible :
– One Ramp Mode. In this mode, all the 3 PSCOUTnB outputs are edge-aligned and
the 3 PSCOUTnA can be also edge-aligned when setting the same values in the
dedicated registers.
In this mode, the PWM frequency is twice the Center Aligned Mode PWM frequency.
– Center Aligned Mode. In this mode, all the 6 PSC outputs are aligned at the center of
the period. Except when using the same duty cycles on the 3 modules, the edges of
the outputs are not aligned. So the PSC outputs do not commute at the same time,
thus the system which is driven by these outputs will generate less commutation
noise.
In this mode, the PWM frequency is twice slower than in One Ramp Mode.
14.5.3.1 One Ramp Mode (Edge-Aligned)
The following figure shows the resultant outputs PSCOUTnA and PSCOUTnB operating in one
ramp mode over a PSC cycle.
One PSC Cycle
UPDATE
PSC Counter Value