Tutorial — Practice 4: PWM

What you will build

Generate PWM with Timer2 and CCP1 to control brightness or motor speed.

Steps in this tutorial

1. 1. Calculate PR2 for PWM frequency
2. 2. Configure Timer2
3. 3. Enable CCP1 in PWM mode
4. 4. Vary duty cycle in your application
5. 5. Measure and document in Proteus

1. 1

   Calculate PR2 for PWM frequency

   With 20 MHz crystal and Timer2 prescaler = 4, PWM frequency is `Fosc / (4 × prescaler × (PR2 + 1))`. For ~1 kHz with PR2=249: verify on paper first. Record PR2 and prescaler in your report.

   Tip: Theory: /en/pwm/

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2. 2

   Configure Timer2

   Write T2CON (prescaler 1:4 or 1:16 per your calculation), load PR2, and enable Timer2. RC2/CCP1 must be output (`TRISC` bit 2 = 0).

   
   								        MOVLW   D'249'
           MOVWF   PR2
           MOVLW   B'00000101'   ; T2CKPS prescaler, encender TMR2
           MOVWF   T2CON
           BCF     TRISC, 2
   							

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3. 3

   Enable CCP1 in PWM mode

   CCP1CON bits 3:0 = 1100 (PWM). CCP1CON bits 5:4 + CCPR1L set duty (10 bits). Start at 50%: `CCPR1L = PR2 / 2`.

   
   								        MOVLW   B'00001100'
           MOVWF   CCP1CON
           MOVLW   D'124'         ; ~50% si PR2=249
           MOVWF   CCPR1L
   							

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4. 4

   Vary duty cycle in your application

   Connect an LED or motor on RC2. Change `CCPR1L` from keyboard, potentiometer (ADC), or a table. Observe brightness or speed. Adapt the pin if you use CCP2 on another port.
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5. 5

   Measure and document in Proteus

   Use the virtual scope on RC2. Capture frequency and duty. Compare with your theoretical calculations. Include formulas in the report.
   I completed this step

Supporting theory

Before coding, review PWM / CCP: PR2 calculation, duty cycle, and Timer2 setup.

What your code should do

1. Calculate PR2 for the target PWM frequency (e.g. ~1 kHz).
2. Configure T2CON, PR2, and CCP1CON in PWM mode.
3. Write duty to CCPR1L and CCP1CON bits.
4. Connect load on RC2/CCP1 and vary duty (potentiometer + ADC optional).

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