The PSC is based on the use of a free-running 12-bit counter (PSC counter). This counter is able to count up to a top value
determined by the contents of POCR_RB register and then according to the selected running mode, count down or reset to
zero for another cycle.
As can be seen from the block diagram Figure 14-1, the PSC is composed of 3 modules.
Each of the 3 PSC modules can be seen as two symetrical entities. One entity named part A which generates the output
PSCOUTnA and the second one named part B which generates the PSCOUTnB output.
Each module has its own PSC Input circuitry which manages the corresponding input.
14.5 Functional Description
14.5.1 Generation of Control Waveforms
In general, the drive of a 3 phase motor requires the generation of 6 PWM signals. The duty cycle of these signals must be
independently controlled to adjust the speed or torque of the motor or to produce the wanted waveform on the 3 voltage lines
(trapezoidal, sinusoidal...)
In case of cross conduction or overtemperature, having inputs which can immediately disable the waveform generator’s
outputs is desirable.
These considerations are common for many systems which require PWM signals to drive power systems such as lighting,
DC/DC converters.
14.5.2 Waveform Cycles
Each of the 3 modules has 2 waveform generators which jointly compose the output signal.
The first part of the waveform is relative to part A or PSCOUTnA output. This waveform corresponds to sub-cycle A in the
following figure.
The second part of the waveform is relative to part B or PSCOUTnB output. This waveform corresponds to sub-cycle B in the
following figure.
The complete waveform is terminated at the end of the sub-cycle B, whereupon any changes to the settings of the waveform
generator registers will be implemented, for the next cycle.
The PSC can be configured in one of two modes (1Ramp Mode or Centered Mode). This configuration will affect the
operation of all the waveform generators.
Figure 14-2. Cycle Presentation in One Ramp Mode
One PSC Cycle
Sub Cycle A
Sub Cycle A
PSC Counter Value
Update
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ATmega16/32/64/M1/C1 [DATASHEET]
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
