Datasheet

ST72321Rx ST72321ARx ST72321Jx
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ON-CHIP PERIPHERALS (Cont’d)
Independent PWM signal generation
This mode allows up to four Pulse Width Modulat-
ed signals to be generated on the PWMx output
pins with minimum core processing overhead.
This function is stopped during HALT mode.
Each PWMx output signal can be selected inde-
pendently using the corresponding OEx bit in the
PWM Control register (PWMCR). When this bit is
set, the corresponding I/O pin is configured as out-
put push-pull alternate function.
The PWM signals all have the same frequency
which is controlled by the counter period and the
ARTARR register value.
f
PWM
= f
COUNTER
/ (256 - ARTARR)
When a counter overflow occurs, the PWMx pin
level is changed depending on the corresponding
OPx (output polarity) bit in the PWMCR register.
When the counter reaches the value contained in
one of the output compare register (OCRx) the
corresponding PWMx pin level is restored.
It should be noted that the reload values will also
affect the value and the resolution of the duty cycle
of the PWM output signal. To obtain a signal on a
PWMx pin, the contents of the OCRx register must
be greater than the contents of the ARTARR reg-
ister.
The maximum available resolution for the PWMx
duty cycle is:
Resolution = 1 / (256 - ARTARR)
Note: To get the maximum resolution (1/256), the
ARTARR register must be 0. With this maximum
resolution, 0% and 100% can be obtained by
changing the polarity.
Figure 38. PWM Auto-reload Timer Function
Figure 39. PWM Signal from 0% to 100% Duty Cycle
DUTY CYCLE
REGISTER
AUTO-RELOAD
REGISTER
PWMx OUTPUT
t
255
000
WITH OEx=1
AND OPx=0
(ARTARR)
(PWMDCRx)
WITH OEx=1
AND OPx=1
COUNTER
COUNTER
PWMx OUTPUT
t
WITH OEx=1
AND OPx=0
FDh FEh FFh FDh FEh FFh FDh FEh
OCRx=FCh
OCRx=FDh
OCRx=FEh
OCRx=FFh
ARTARR=FDh
f
COUNTER