Electronic – PIC18F1320 with 4 separate PWM channels and C18 compiler for an RGB LED

picpwm

I'm pretty new to microcontroller programming and I find the lack of documentation on certain features of PICs with C18 compiler frustating. I've been trying to make a simple 3-color-led light up using PWM for each channel but I can't seem to figure out how to use the ECCP enhanced PWM feature of PIC18F1320.

I've got a couple of other PIC18Fs (2550, 1320, 4450 to name a few) so trying other ones is an option, but I specifically got the 1320s because they had Enhanced PWM, Page 115 in the Datasheet.

I've got some code to slowly pulsate 1 led channel using normal PWM, I've attached it here. Im using the pwm.h include and its helper functions, but people have mentioned just setting the registers manually. Im confused as to how I would set the specific ones the manual mentions, they are in a format Im not used to, something like CCP1M<3:2> =/

I keep finding scraps of useful material out there and constantly learning about whats inside these things, so hopefully with your help i'll be able to make sense of all of this and make some basic code to light up this damn LED =D

Best Answer

Note that the PIC18F1320 still has only a single PWM module. This means you cannot have 3 independent PWM output signals. The '4 output signals' in the manual means that the PWM module can drive all 4 legs of a H-bridge with the proper timing - but the depend on each other (see figure 15-5 in the data sheet).

Regarding the register descriptions: CCP1M<3:2> means the bits 2 and 3 of the CCP1M select bits (these are actually 4 bits, but only the upper two ones are of interest there). The easiest way to set these registers is by using the register descriptions:

CCP1CONbits.CCP1M=42;

You can also use CCP1CON directly, but then you write all bits of this register directly.

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Multiplexing AVR (ATMega328) PWM within Interrupts

Ok, I figured it out. The problem was that I was leaving the PWM frequency at the default and using a very high multiplexing rate.

By default, the prescalers are set to 64 making the frequency on the timers I was using (0 and 2) 976.5625Hz. But I was using a multiplexing rate of 6400 Hz... just because this was what I used on a different project that didn't include PWM. The main problem here was that it couldn't get any PWM cycles in during a single multiplex cycle.

So, I switched to using a prescale of 8 on my PWMs, bringing the frequency to ~8Khz and set the multiplex rate to 1000Hz, so that way, it gets in about 8 PWM cycles per multiplex cycle. I could probably decrease the multiplex rate even more, but it's a fine line before you start to see flicker.

Also, I found out that when you update the PWM duty cycle (like by setting OCR2A) it take some time before it actually takes effect. So if I move on with the multiplex right away, the PWM values will sort of bleed over into the next LED. So I added some logic where on the first time through the multiplex ISR, it disables all anodes and sets the PWM values. Then on the next time through, it just enables the needed anode. This is what the flip_flop variable is for.

void setup()
{
  //Setup outputs for anodes
  DDRB |= (_BV(PINB0) | _BV(PINB1) | _BV(PINB2));


  //Setup Timer2 Interrupts
  TCCR2A = _BV(COM2A1) | _BV(WGM21) | _BV(WGM20); //Fast PWM mode on OCR2A (PINB3 - Digital 11)
  TCCR2B = _BV(CS21); //8 Prescaler
  OCR2A = 255;

  //Setup Multiplex ISR on Timer1
  // set compare match register for 1000hz 
  OCR1A = 16000;
  // turn on CTC mode
  TCCR1B |= _BV(WGM12);

  TCCR1B |= PRESCALE1_1;  
  // enable timer compare interrupt
  TIMSK1 |= _BV(OCIE1A);
}

volatile uint8_t col = 0;
bool flip_flop = false;
ISR(TIMER1_COMPA_vect)
{
  //Set all anodes to LOW
  if(!flip_flop)
  {
    PORTB &= ~(_BV(PINB0) | _BV(PINB1) | _BV(PINB2));

    //Faking it here: Basically simulating that LED 0 is on but LEDs 1 and 2 are not.
    //Note that because the PWM is on the cathode, 255 is OFF and 0 is full brightness.
    if(col == 0)
      OCR2A = 0;
    else
      OCR2A = 255;
  }



  if(flip_flop)
  {
    //Turn on JUST the LED that we want.
    PORTB |= _BV(col);

    //Step through the LEDs
    col++;
    if(col > 2)
    {
      col = 0;
    } 
  }

  flip_flop = flip_flop ? false : true;
}

Electronic – Toggle LED on when Button is pressed PIC

Your problem is probably caused by the analogue module. According to page 84 of the data sheet you linked the ADCON1 register needs to be set correctly to enable digital functions on PORTA.

A value of 0b111 is likely to make your code work (but see other answers about debouncing). Various other combinations of values are available in the table for REGISTER 11-2:

This type of configuration is common on the smaller 12F and 16F devices, which lack the ability to individually select analogue or digital per-pin.

As Spehro notes in the comments there are a number of ways to find which registers are associated with a port. The easiest is TABLE 4-2: SUMMARY OF REGISTERS ASSOCIATED WITH PORTA, which looks like this:

TABLE 4-2 SUMMARY OF REGISTERS ASSOCIATED WITH PORTA

This table becomes even more useful on large devices that have lots of functions such as extended analog features or capture and compare. Many of these need to be disabled after reset (e.g. comparators) and some might interfere unintentionally if misconfigured (e.g. MSSP).

Note that this table also shows that the 16LF76 does not have LATx registers, so other comments above can be safely ignored for this device.

Best Answer

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Multiplexing AVR (ATMega328) PWM within Interrupts

Electronic – Toggle LED on when Button is pressed PIC

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