MEC1322 datasheet(287/456 Pages) MICROCHIP

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 2014 - 2015 Microchip Technology Inc.

DS00001719D-page 287

MEC1322

The PWM clock source to the PWM Down Counter, used to generate a duty cycle and frequency on the PWM, is deter-

mined through the Clock select[1] and Clock Pre-Divider[6:3] bits in the PWMx Configuration Register register.

The PWMx Counter ON/OFF Time registers determine both the frequency and duty cycle of the signal generated on

PWM_OUTPUT as described below.

The PWM frequency is determined by the selected clock source and the total on and off time programmed in the PWMx

Counter ON Time Register and PWMx Counter OFF Time Register registers. The frequency is the time it takes (at that

clock rate) to count down to 0 from the total on and off time.

The PWM duty cycle is determined by the relative values programmed in the PWMx Counter ON Time Register and

PWMx Counter OFF Time Register registers.

The PWM Frequency Equation and PWM Duty Cycle Equation are shown below.

FIGURE 25-3:

PWM FREQUENCY EQUATION

In Figure 25-3, the ClockSourceFrequency variable is the frequency of the clock source selected by the Clock Select

bit in the PWMx Configuration Register, and PreDivisor is a field in the PWMx Configuration Register. The PWMCoun-

terOnTime, PWMCounterOffTime are registers that are defined in Section 25.11, "EC-Only Registers".

FIGURE 25-2:

BLOCK DIAGRAM OF PWM CONTROLLER

Note:

In Figure 25-2, the 48 MHz Ring Oscillator is represented as CLOCK_HIGH and 100kHz_Clk is repre-

sented as CLOCK_LOW.

PWM BLOCK

PWM Duty Cycle &

Frequency Control

PWM_ OUTPUT

PWM Registers

CLOCK_HIGH

CLOCK_LOW

Invert_PWM

Clock Select

16-bit down

counter

EC I/F

Clock

Pre-

Divider

(15:0)

PWM Frequency

PreDivisor 1

()

--------------------------------------------

ClockSourceFrequency

()

PWMCounterOnTime PWMCounterOffTime

()

-------------------------------------------------------------------------------------------------------------------------------

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