Specifications:
Microcontroller: PIC18f4520
Crystal: 4 MHz
Language: C Programming (not assembly codes)

Basically I'm trying to blink a LED using PWM to enable the on-time to be variable. However, I can't seem to blink the LED without using the LED toggle and delay functions. By using the toggle function, I have found that the on-time cannot be changed.

May anyone give me an idea on what I can do to go around this?

Post your code, and compiler version.

At 4MHz the PWM is going to be pretty fast. How slow do you want it to blink?

What do you figure your PWM speed is? Anything faster than 30Hz may be impossible to see as a flash.

Code:

PORTBbits.RB1 = PORTCbits.RC2;     //blinking LED according to PWM
  while(1);

Do you see anything wrong here? How will RB1 change?

Internal oscillator support - 31 kHz to 8 MHz, up to 32 MHz with 4X PLL

looks like you could set that for any thing you would want

If the oscillator used is big, does the PR2 value increase as well? Is the crystal oscillator and the internal oscillator support two different things?

Code:

PORTBbits.RB1 = PORTCbits.RC2;     //blinking LED according to PWM
  while(1);

By the way, can anyone tell me what is wrong (I know it's wrong) with this statement and how do I rewrite it?

I'm not good with C but the osc can be change the Internal oscillator clock from 8mhz 4mhz 2mhz 1 mhz and lower down to 32khz which would give you real slow pwm and if your using a CRYSTAL/CERAMIC RESONATOR your can turn it off and use Internal oscillator

Code:

 while(1); 

What is the intention of this?! while(1); does "loop in one spot" it will never change / set / do anything .. the app will just "stand still" at that position....

disregarding the config bits etc ..

Code:

#include <p18f4520.h>

void main ( )
{
  TRISB = 0;
  TRISC = 0b11111011; // RC2 as output
  T2CON = 0b00000101; // Timer 2 On, postscale = 1:1, prescale = 1:4
  PR2 = 64; // Set PR2 = 64 for 52 us
  CCPR1L = 0b00001101; // CCPR1L:CCP1CON<5:4> = 52
  CCP1CON = 0b00001111; // DC1B1 & DC1B0 = 0, PWM mode
  while(1){
    PORTBbits.RB1 = PORTCbits.RC2; //blinking LED according to PWM
  }
}

In theory this will blink B1 almost the same time as RC2
RC2 is "blinked" by hardware ccp (pwm) module.

if you only need to blink the RC2 then you do not need the b1 part

Code:

#include <p18f4520.h>

void main ( )
{
  TRISB = 0;
  TRISC = 0b11111011; // RC2 as output
  T2CON = 0b00000101; // Timer 2 On, postscale = 1:1, prescale = 1:4
  PR2 = 64; // Set PR2 = 64 for 52 us
  CCPR1L = 0b00001101; // CCPR1L:CCP1CON<5:4> = 52
  CCP1CON = 0b00001111; // DC1B1 & DC1B0 = 0, PWM mode
  while(1); // DO NOTHING - hw pwm module will blink led
}

I do not see the config here but if you are running it at 4MHz the speed of the pwm will be too fast and there is no way you can see the blinking with naked eye .. if you want blinking that you can see, you have to forget about pwm as you cannot make pwm go that slow (max that you can notice is about 100Hz and even that is almost impossible to tell ... the 15Hz is kinda max for "noticeable" blink) and PWM usually do not go under few KHz because:

PWM Period = [(PR2) + 1] • 4 • TOSC • (TMR2 Prescale Value)

your TOSC is 1/4000000, max TMR2 prescale is 16, max PR2 is 255 so max period is

256 * 4 * (1/4000000) * 16 = 0.004096 => 1/0.004096 = 244.14Hz

So with 4MHz the lowest you can go is 244Hz - there is NO WAY you can see that with naked eye. not to mention that you are using 1:4 prescale and not 1:16 so your led is blinking at almost 1KHz

If you need to be able to see the led blink, use the delay function

Code:

#include <p18f4520.h>

void main ( )
{
  TRISB = 0;
  TRISC = 0b11111011; // RC2 as output
  LATBbits.LATB1 = 0;
  LATCbits.LATC2 = 0;

  while(1){
    LATBbits.LATB1 ^= 1;
    LATCbits.LATC2 ^= 1;
    Delay10KTCYx(200); //wait 2000000 cycles
  }
}

btw, you are probably trying:

Code:

#include <p18f4520.h>

void main ( )
{
  unsigned char dcycle;
  TRISB = 0;
  TRISC = 0b11111011; // RC2 as output
  T2CON = 0b00000101; // Timer 2 On, postscale = 1:1, prescale = 1:4
  PR2 = 64; // Set PR2 = 64 for 52 us
  CCPR1L = 0b00001101; // CCPR1L:CCP1CON<5:4> = 52
  CCP1CON = 0b00001111; // DC1B1 & DC1B0 = 0, PWM mode

   // the led is now pwm'd with 1KHz on RC2

  dcycle = 0;
  while(1){ // loop forever
     // change the brightness of the LED by changing PWM DC
     // PWM Duty Cycle = (CCPRXL:CCPXCON<5:4>) • TOSC • (TMR2 Prescale Value)
     CCPR1L = dcycle++;
     Delay10KTCYx(20); //wait 200000 cycles
  }
}

this will change the brightness of your led on RC2 every 200ms (only 8bit resolution - 10 bit resolution is possible but not needed for this example) 256 times and then will start from scratch

and .. if you want to blink and not to smoothly light more :

Code:

#include <p18f4520.h>

void main ( )
{
  TRISB = 0;
  TRISC = 0b11111011; // RC2 as output
  T2CON = 0b00000101; // Timer 2 On, postscale = 1:1, prescale = 1:4
  PR2 = 64; // Set PR2 = 64 for 52 us
  CCPR1L = 0b00001101; // CCPR1L:CCP1CON<5:4> = 52
  CCP1CON = 0b00001111; // DC1B1 & DC1B0 = 0, PWM mode
  // the led is now pwm'd with 1KHz on RC2

  while(1){ // loop forever
     //LED ON
     CCPR1L = 0xFF;
     Delay10KTCYx(20); //wait 200000 cycles
     //LED OFF
     CCPR1L = 0;
     Delay10KTCYx(20); //wait 200000 cycles
  }
}

and .. for the end of mine involvement .. if you are using C18 why don't you use available libraries ... there's pwm library .. :

Function prototypes
#include <pwm.h>
void OpenPWMx ( char PR2 ); // Configure PWM channel x.
void SetDCPWMx ( unsigned int dutycycle ); // Write a new duty cycle value to PWM channel x.
void ClosePWMx ( void ); // Disable PWM channel x.

Notes:

1. PR2 can be any value from 0x00 to 0xff. This value determines the PWM frequency by using the following formula:
PWM period =[(PR2) + 1] x 4 x TOSC x TMR2 prescaler

2. The value of dutycycle can be any 10-bit number. Only the lower 10-bits of dutycycle are written into the duty cycle registers. The duty cycle determines the high time of the PWM waveform.

3. PWM uses TIMER2 for time base. In addition to opening the PWM, TIMER2 must also be opened with an OpenTimer2(...) statement before the PWM will operate. See the other manual for the timer functions.

4. TIMER2 postscaler is not used in the determination of the PWM frequency. TIMER2 postscaler could be used to generate TMR2 interrupts at a different frequency than the PWM output.

Originally Posted by arhi

and .. if you want to blink and not to smoothly light more :

Code:

  while(1){ // loop forever
     //LED ON
     CCPR1L = 0xFF;
     Delay10KTCYx(20); //wait 200000 cycles
     //LED OFF
     CCPR1L = 0;
     Delay10KTCYx(20); //wait 200000 cycles
  }

May i know why is CCPR1L = 0xFF instead of my desired CCPR1L value?

I've tried changing the value of CCPR1L to different values and i noticed that has effect for buzzer tone. However, the blinking of the LED looks the same. How do I know if PWM has any effect on the LED?