PC87591L datasheet(147/437 Pages) NSC

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Embedded Controller Modules (Continued)

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4.8

PULSE WIDTH MODULATOR (PWM)

The PWM module generates eight 8-bit PWM outputs; each may have a different duty cycle. A common 8-bit clock pre-scaler

and an 8-bit down-counter determine the cycle time, the minimal possible pulse width and the duty cycle steps.

4.8.1

Features

●

Eight PWM outputs

●

One 8-bit fully programmable pre-scaler

●

One 8-bit fully programmable down-counter

●

8-bit duty cycle control per output

●

Programmable polarity per output

●

Low Power mode

4.8.2

Functional Description

The PWM generates eight 8-bit PWM outputs, PWM0 to PWM7. The Duty Cycle registers 0 to 7 (DCRi, i = 0 to 7) control

the duty cycle of PWM0 to PWM7 output signals, respectively. The Cycle Time register (CTR) controls the cycle time and

duty cycle steps of all outputs.

The PWM use the core domain clock as a reference for its activities. The pre-scaler divider divides the PWM input clock by

a pre-programmable ratio of 1:1 through 1:256, as defined by the Clock Pre-Scaler register (PRSC).

The PWM cycle is defined in terms of cycles of the pre-scaler output clock. It has a period of (CTR +1) cycles, out of which

the signal will be high for DCRi cycles. INVPi, when set, may be used to inverse this behavior.

The cycle period is defined by the 8-bit down-counter. It counts using the output clock from the pre-scaler divider, starting

from the value held in CTR register down to 0. When it reaches 0, the down-counter restarts from the CTR value.

The DCRi register defines the number of clock cycles during which PWMi signal is high during the complete down-counter

cycle.

If Inverse PWMi bit (INVPi) in PWM Polarity register (PWMPOL) is active (1), the DCRi register defines the number of clock

cycles during which PWMi signal is low in each of the down-counter complete cycles.

Figure 51 is a functional block diagram of the PWM module.

Figure 51. PWM Block Diagram

8-Bit Pre-Scaler

Counter

Input

Clock

8-Bit

Down-Counter

Cycle Time

Duty Cycle

Compare

Duty Cycle

Compare

Clock Pre-Scaler

Down-Counter == CTR

PWM0

Q Q

PWM7

INVPi

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