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The Pulse Width Modulation Module / C167 Period Registers PPx The 16-bit period register PPx of a PWM channel determines the period of a PWM cycle, ie. the frequency of the PWM signal. This register is buffered with a shadow register. The shadow register is loaded from the respective PPx register at the beginning of every new PWM cycle, or upon a write access to PPx, while the timer is stopped. The CPU accesses the PPx register while the hardware compares the contents of the shadow register with the contents of the associated counter PTx. When a match is found between counter and PPx shadow register, the counter is either reset to 0000H, or the count direction is switched from counting up to counting down, depending on the selected operating mode of that PWM channel. Note: For the register locations please refer to the table below. Pulse Width Registers PWx This 16-bit register holds the actual PWM pulse width value which corresponds to the duty cycle of the PWM signal. This register is buffered with a shadow register. The CPU accesses the PWx register while the hardware compares the contents of the shadow register with the contents of the associated counter PTx. The shadow register is loaded from the respective PWx register at the beginning of every new PWM cycle, or upon a write access to PWx, while the timer is stopped. When the counter value is greater than or equal to the shadow register value, the PWM signal is set, otherwise it is reset. The output of the comparators may be described by the boolean formula: PWM output signal = [PTx] ≥ [PWx shadow latch]. This type of comparison allows a flexible control of the PWM signal. Note: For the register locations please refer to the table below. PWM Module Channel Specific Register Addresses Register Address Reg. Space Register Address Reg. Space PW0 FE30H / 18H SFR PT0 F030H / 18H ESFR PW1 FE32H / 19H SFR PT1 F032H / 19H ESFR PW2 FE34H / 1AH SFR PT2 F034H / 1AH ESFR PW3 FE36H / 1BH SFR PT3 F036H / 1BH ESFR PP0 F038H / 1CH ESFR PP1 F03AH / 1DH ESFR PP2 F03CH / 1EH ESFR Note: These registers are not bit-addressable. PP3 Semiconductor Group 15-8 F03EH / 1FH ESFR
