Freescale Semiconductor MCF51QE128RM Channel Event Interrupt Description, Center-Aligned PWM Case

Timer/PWM Module (S08TPMV3)

17.6.2.1.2Center-Aligned PWM Case

When CPWMS is set, TOF is set when the timer counter changes direction from up-counting to down-counting at the end of the terminal count (the value in the modulo register). In this case, TOF corresponds to the end of a PWM period.

17.6.2.2Channel Event Interrupt Description

The meaning of channel interrupts depends on the channel’s current mode (input-capture, output-compare, edge-aligned PWM, or center-aligned PWM).

17.6.2.2.1Input Capture Events

When a channel is configured as an input capture channel, the ELSnB and ELSnA control bits select no edge (off), rising edges, falling edges, or any edge as the edge that triggers an input capture event. When the selected edge is detected, the interrupt flag is set. The flag is cleared by the two-step sequence described in Section 17.6.2, “Description of Interrupt Operation.”

17.6.2.2.2Output Compare Events

When a channel is configured as an output compare channel, the interrupt flag is set each time the main timer counter matches the 16-bit value in the channel value register. The flag is cleared by the two-step sequence described Section 17.6.2, “Description of Interrupt Operation.”

17.6.2.2.3PWM End-of-Duty-Cycle Events

There are two possibilities for channels configured for PWM operation. When the channel is configured for edge-aligned PWM, the channel flag is set when the timer counter matches the channel value register that marks the end of the active duty cycle period. When the channel is configured for center-aligned PWM, the timer count matches the channel value register twice during each PWM cycle. In this CPWM case, the channel flag is set at the start and at the end of the active duty cycle period, when the timer counter matches the channel value register. The flag is cleared by the two-step sequence described Section 17.6.2, “Description of Interrupt Operation.”

MCF51QE128 MCU Series Reference Manual, Rev. 3

354 Freescale Semiconductor

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