Pulse-Width Modulator for Motor Control (PWMMC)
Timebase
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0 Advance Information
MOTOROLA Pulse-Width Modulator for Motor Control (PWMMC) 141
9.4 Timebase
This section provides a discussion of the timebase.
9.4.1 Resolution
In center-aligned mode, a 12-bit up/dow n counter is used to create the
PWM period. Therefore, the PWM resolution in center-aligned mode is
two clocks (highest resolution is 250 ns @ fOP = 8 MHz) as shown in
Figure 9-3. The up/down counter uses the value in the timer modulus
register to determine its maximum count. The PWM period will equal:
[(timer modulus) x (PWM clock period) x 2].
Figure 9-3. Center-Aligned PWM (Positive Polarity)
UP/DOWN COUNTER
MODULUS = 4
PWM = 0
PWM = 1
PWM = 2
PWM = 3
PWM = 4
PERIOD = 8 X (PWM CLOCK PERIOD)