PIC18F1330 & PWM Update.

[bsodmike]

Hi folks,

Thanks to many people here I was pointed in the direction of the 18F1330 PIC featuring 3 on-board PWMs.

I've gotten as far as this, simulated in MPLAB. Coded with Hi-Tech's PICC18 STD compiler:

**broken link removed**

I was able to configure the PIC to only enable PWM on the 'odd' port pins, and output a 500Hz signal, which works nicely as it brings the PWM resolution to a maximum of 13.96 (odd). This works out to '16000' representing a 100% duty cycle, which is a nice round number.

In the above simulation I had the code loop from 0% to 100% duty cycle and at the end to flip the state on the other 'RB' pins (configured as I/O rather than PWM).

Next up: Implement a serial 'receive' interrupt to adjust the duty cycle on the fly based on data received from a PC.

 

[jxd704]

Help

Hi mate, I am new to PIC, and can I take a look at ur code, I am trying to generate a PWM output with a steady duty cycle but still not working. So could you send me a copy of the code to deathknightdjc@hotmail.com , so I could learn somethin from it. TY

 

[kfet]

Hi mate, I am new to PIC, and can I take a look at ur code, I am trying to generate a PWM output with a steady duty cycle but still not working. So could you send me a copy of the code to deathknightdjc@hotmail.com , so I could learn somethin from it. TY

same here if this is possible. dskevin@hotmail.com, thanks in advance.

 

[bsodmike]

PWM Code Snippet...

Apologies for the extremely late response. Mind you, I have not looked at this code in quite some time but this is what I was able to dig up. I do not like the practice of handing "everything" on a platter - especially as I achieved this with much hard work.

Intro & Initialisation

The following code was compiled with Hi-Tech PICC18 STD v9.51PL1 @ Global (9) Optimization. This code was submitted to King's College London for the award of MSc (Distinction) in Mechatronics as part of my thesis titled "Mobile Autonomous Omni-Directional Robotic Vehicle Control for Indoor Navigation".

First you need to configure the PIC:

#ifdef _18F4331
// Settings for PIC18F4331

//__CONFIG(1,RCCLKO & IESODIS & FCMDIS); //RCCLKO [CONFIG1H<0:3>: 0xF9]: Internal RC, RA6=Fosc/4 & RA7=IO
__CONFIG(1,RCIO & IESODIS & FCMDIS); //RCIO [CONFIG1H<0:3>: 0xF8]: Internal RC, RA6=IO & RA7=IO
__CONFIG(2,BORDIS & PWRTDIS & WDTDIS);
//__CONFIG(3,MCLRDIS & PWM4RD5); //Configure PWM4 on alternate pin, RD5
__CONFIG(3,MCLRDIS);
__CONFIG(4,DEBUGDIS & STVRDIS & LVPDIS);
__CONFIG(5,UNPROTECT);
__CONFIG(6,WRTEN);
#else
	#error Unsupported PICmicro MCU selected
#endif

PIC Init Routine with PWM Code

This is the entire function as from my complete code.

// Init Routine
void init()
{
	//initialize clock and i/o ports
	OSCCON = 0x70; 		//OSCCON<6:4>: INTOSC set as 8MHz
	
	TRISA = 0x00; 		//defined as outputs
	TRISB = 0x00; 		//defined as outputs
	TRISC = 0x00; 		//defined as outputs
	TRISD = 0x00; 		//defined as outputs
	TRISE = 0x00; 		//defined as outputs
	PORTA = 0x00;
	PORTB = 0x00;
	PORTC = 0x00;
	PORTD = 0x00;
	PORTE = 0x00;		
	
	//configure a/d module - essentially disable it!
	ADCON0 = 0b00000000;
	ADCON1 = 0b00011111;
	ADCON2 = 0b10111111;
	ADON = 0; //A/D Converter module is disabled

	//Configure Power Control PWM Module

	/*
	At 8MHz, to obtain a PWM frequency of 500Hz
    
	TPWM 	= time period of PWM frequency
    PTPER 	= 12-bit period register PTPERL and PTPERH
    PTMRPS 	= PWM time base prescaler
     
           (PTPER+1)*PTMRPS     (3999+1) * 1
    TPWM = ----------------  =  ------------ = 0.002s
                Fosc/4           8000000/4
    
    Frequency = 1/TPWM = 500Hz
    
    PWM resolution (bits resolution for duty cycle):
    
                 log(8MHz/500Hz)
    Resolution = ------------------ = 13.96578428 = ~14 bits
                      log(2)
	*/

	//initialize PWM and timers
	PTCON0 	= 0b00000000; 	//Postscale 1:1, Fosc/4 Prescale 1:1, Free Running Mode
  	PTCON1 	= 0b10000000;   //Time base in ON, Time base counts up
  	PWMCON0 = 0b01111111;  	//All odd PWM I/O pins enabled for PWM output, Independent mode for all pins
							//PWMCON0 = 0b01110111; for PIC18F1330
  	PWMCON1 = 0b00001001;  	//Postscale 1:1, special event on count downwards, updates from Duty Cycle and Period Buffers enabled

	//4095d = 0xFFFh = 001111 11111111
	//16000 = 0x3E80 = 111110 10000000 = 62 80
	//16256 = 0x3F80 = 111111 10000000 = 63 80
	//16383 = 0x3FFF = 111111 11111111 = 63 255

  	PDC0H = 0;				//Duty Cycle control for PWM0/1
  	PDC0L = 0;   			//Duty Cycle control for PWM0/1
	//PDC0H = 0b001111;		//Duty Cycle control for PWM0/1
	//PDC0L = 0b11111111;   //Duty Cycle control for PWM0/1

  	PDC1H = 0;      		//Duty Cycle control for PWM2/3
  	PDC1L = 0;   			//Duty Cycle control for PWM2/3

  	PDC2H = 0;       		//Duty Cycle control for PWM4/5
  	PDC2L = 0;    			//Duty Cycle control for PWM4/5

  	PDC3H = 0;       		//Duty Cycle control for PWM6/7
  	PDC3L = 0;    			//Duty Cycle control for PWM6/7
	
 	//Period control for all PWM output  (set at 500 Hz)
  	//PTPERH = 0b1111;
  	//PTPERL = 0b10011111; 	//3999d = 0xF9Fh = H[1111] L[10011111] 
  	PTPERH = 0xF9F >> 8;
  	PTPERL = 0xF9F; 		//3999d = 0xF9Fh = H[1111] L[10011111] 

	//Define PWM Port Definitions
	#define M1 		PDC0H
	#define M2 		PDC1H
	#define M3 		PDC2H
	#define PWM7	PDC3H //free PWM output, PWM7/RD7

	//Define Motor Direction and Brake Pins
	#define M1_DIR	RD0
	#define M1_BR	RD1
	#define M2_DIR	RD2
	#define M2_BR	RD3
	#define M3_DIR	RD4
	#define M3_BR	RD5

	//initialise EUSART
	init_EUSART();
}

The main routine runs something like this:

// Main Service Loop
void main(void)
{
	//local variables declared here	

	//initialise
	init();
	/* MAIN LOOP */
	while(1)
	{
		//code never exits from this infinite loops.
	}
}

Of course, my code included interrupt driven serial communications. The motor control routine looked something like this:

void motor_test()
{
	short i=0;

	// Motor ramp test
	for (i=0;i<50;i++)
	{
		M1 = i+10;
		M2 = i+10;
		M3 = i+10;
		DelayMs(80);
	}

	DelayS(5); //persist PWM @ 95% for 5s.

	for (i=60;i>10;i--)
	{
		M1 = i-10;
		M2 = i-10;
		M3 = i-10;
		DelayMs(80);
	}

	DelayS(1);

	M1 = 0;
	M2 = 0;
	M3 = 0;
}

I have uploaded a video of this particular segment of code in action. The PWM signal generated is gradually ramped from a duty cycle of 0% to 100%.

MARV: PWM Ramp Test
MARV: Motor Speed Test
MARV: First Full Motor Test

You can see **broken link removed**.

**broken link removed**

Hope this helps!

Cheers,
Mike.

 

[Mr RB]

That's a nice looking robot!

Elegant construction and very neatly implemented.