MC68HC908MR8 Datasheet, PDF (146/372 Pages) Motorola, Inc – Microcontrollers

Pulse-Width Modulator for Motor Control
9.4 Timebase
This subsection provides for a discussion of the timebase.
9.4.1 Resolution
In center-aligned mode, a 12-bit up/down counter is used to create the
PWM period. Therefore, the PWM resolution in center-aligned mode is
two clocks (highest resolution is 250 ns @ f_OP = 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
For edge-aligned mode, a 12-bit up-only counter is used to create the
PWM period. Therefore, the PWM resolution in edge-aligned mode is
one clock (highest resolution is 125 ns @ f_OP = 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 5.4 CONFIG Bits.
Technical Data
146
MC68HC908MR8 — Rev 4.1
Pulse-Width Modulator for Motor Control (PWMMC) Freescale Semiconductor