ST10F280_12 datasheet(86/239 Pages) STMICROELECTRONICS

86 / 239 page

PWM module

ST10F280

86/239

Doc ID 8673 Rev. 3

Figure 22.

Operation and output waveform in burst mode

Single shot mode

Single shot mode is selected by setting the respective bit PSx in register XPWMCON1 to ‘1’.

This mode is available for XPWM channels 2 and 3.

In this mode the timer XPTx of the respective XPWM channel is started via software and is

counting up until it reaches the value in the associated period shadow register. Upon the

next count pulse the timer is cleared to 0000h and stopped via hardware, i.e. the respective

PTRx bit is cleared. The XPWM output signal is switched to high level when the timer

contents are equal to or greater than the contents of the pulse width shadow register. The

signal is switched back to low level when the respective timer is cleared, i.e. is below the

pulse width shadow register. Thus starting a XPWM timer in single shot mode produces one

single pulse on the respective port pin, provided that the pulse width value is between 0000h

and the period value. In order to generate a further pulse, the timer has to be started again

via software by setting bit PTRx (see Figure 23).

After starting the timer (i.e. PTRx = ‘1’) the output pulse may be modified via software.

Writing to timer XPTx changes the positive and/or negative edge of the output signal,

depending on whether the pulse has already started (i.e. the output is high) or not (i.e. the

output is still low). This (multiple) re-triggering is always possible while the timer is running,

i.e. after the pulse has started and before the timer is stopped.

Loading counter XPTx directly with the value in the respective XPPx shadow register will

abort the current PWM pulse upon the next clock pulse (counter is cleared and stopped by

hardware).

By setting the period (XPPx), the timer start value (XPTx) and the pulse width value (XPWx)

appropriately, the pulse width (tw) and the optional pulse delay (td) may be varied in a wide

range.

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