ST10F280_12 datasheet(84/239 Pages) STMICROELECTRONICS

84 / 239 page

PWM module

ST10F280

84/239

Doc ID 8673 Rev. 3

Figure 20.

Operation and output waveform in mode 0

Mode 1: symmetrical PWM generation (center aligned PWM)

Mode 1 is selected by setting the respective bit XPMx in register XPWMCON1 to ‘1’. In this

mode the timer XPTx of the respective XPWM channel is counting up until it reaches the

value in the associated period shadow register.

Upon the next count pulse the count direction is reversed and the timer starts counting down

now with subsequent count pulses until it reaches the value 0000H. Upon the next count

pulse the count direction is reversed again and the count cycle is repeated with the following

count pulses.

The XPWM output signal is switched to a high level when the timer contents are equal to or

greater than the contents of the pulse width shadow register while the timer is counting up.

The signal is switched back to a low level when the respective timer has counted down to a

value below the contents of the pulse width shadow register. So in mode 1 this PWM value

controls both edges of the output signal.

Note that in mode 1 the period of the PWM signal is twice the period of the timer:

PWM_PeriodMode1 = 2 * ([XPPx] + 1)

The figure below illustrates the operation and output waveforms of a XPWM channel in

mode 1 for different values in the pulse width register.

This mode is referred to as Center Aligned PWM, because the value in the pulse width

(shadow) register effects both edges of the output signal symmetrically.

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