mc9s12e256 Freescale Semiconductor, Inc, mc9s12e256 Datasheet - Page 406

• Manufacturer Part Number: mc9s12e256
• Description: Hcs12 Microcontrollers 16-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Chapter 12 Pulse-Width Modulator (PWM8B6CV1)
Shown below is the output waveform generated.
12.4.2.6
For center aligned output mode selection, set the CAEx bit (CAEx = 1) in the PWMCAE register and the
corresponding PWM output will be center aligned.
The 8-bit counter operates as an up/down counter in this mode and is set to up whenever the counter is
equal to 0x0000. The counter compares to two registers, a duty register and a period register as shown in
the block diagram in
changes state causing the PWM waveform to also change state. A match between the PWM counter and
the period register changes the counter direction from an up-count to a down-count. When the PWM
counter decrements and matches the duty register again, the output flip-flop changes state causing the
PWM output to also change state. When the PWM counter decrements and reaches 0, the counter direction
changes from a down-count back to an up-count and a load from the double buffer period and duty
registers to the associated registers is performed as described in
Duty.”
effective period is PWMPERx*2.
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The counter counts from 0 up to the value in the period register and then back down to 0. Thus the
PPOLx = 0
PPOLx = 1
Center Aligned Outputs
Changing the PWM output mode from left aligned output to center aligned
output (or vice versa) while channels are operating can cause irregularities
in the PWM output. It is recommended to program the output mode before
enabling the PWM channel.
Figure
E = 100 ns
Figure 12-37. PWM Left Aligned Output Example Waveform
Figure 12-38. PWM Center Aligned Output Waveform
12-35. When the PWM counter matches the duty register the output flip-flop
PWMDTYx
MC9S12E256 Data Sheet, Rev. 1.08
PWMPERx
PERIOD = 400 ns
DUTY CYCLE = 75%
NOTE
Period = PWMPERx*2
Section 12.4.2.3, “PWM Period and
PWMPERx
PWMDTYx
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