Advance Information MC68HC908MR16/MC68HC908MR32 — Rev. 4.0
142 Pulse-Width Modulator for Motor Control (PWM MC) MOTOROLA
Pulse-Width Modulator for Motor Control
For edge-aligned mode, a 12-bit up-only co unter is used to create the
PWM period. Therefore, the PWM resolution in edge-aligned mode is
one clock (highest resolution is125 ns @ fOP = 8 MHz) as shown in
Figure 9-4. Again, the timer modulus register is used to determine the
maximum count. The PWM period will equal:
(timer modulus) x (PWM clock period)
Center-aligned operation versus edge-aligned operation is determined
by the option EDGE. See 5.3 Functional Description.
Figure 9-4. Edge-Aligned PWM (Positive Polarity)
UP-ONLY COUNTER
MODULUS = 4
PWM = 0
PWM = 1
PWM = 2
PWM = 3
PWM = 4
PERIOD = 4 X (PWM
CLOCK PERIOD)