MC9S12XF512 Datasheet, PDF (929/1300 Pages) Freescale Semiconductor, Inc – S12X Microcontrollers

Chapter 20 Pulse Width Modulator with Fault Protection (PMF15B6C) Module
COUNT
12343210
UP/DOWN COUNTER
MODULUS = 4
PWM CLOCK PERIOD
PWM PERIOD = 8 x PWM CLOCK PERIOD
Figure 20-43. Center-Aligned PWM Period
In an edge-aligned operation, the PWM counter is an up counter. The PWM output resolution is one bus
clock cycle.
PWM period = PWM modulus × PWM clock period
COUNT
1234
UP COUNTER
MODULUS = 4
PWM CLOCK PERIOD
PWM PERIOD = 4 x PWM CLOCK PERIOD
Figure 20-44. Edge-Aligned PWM Period
20.4.3.3 Duty Cycle
The signed 16-bit number written to the PMF value registers is the pulse width in PWM clock periods of
the PWM generator output.
Duty cycle = _{M----P--O--M---D--F---U-V---L--A--U--L---S--} × 100
NOTE
A PWM value less than or equal to zero deactivates the PWM output for the
entire PWM period. A PWM value greater than or equal to the modulus
activates the PWM output for the entire PWM period.
Table 20-36. PWM Value and Underflow Conditions
PMFVALx
$0000–$7FFF
$8000–$FFFF
Condition
Normal
Underflow
PWM Value Used
Value in registers
$0000
Center-aligned operation is illustrated in Figure 20-45.
PWM pulse width = (PWM value) × (PWM clock period) × 2
MC9S12XF - Family Reference Manual, Rev.1.18
Freescale Semiconductor
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