PIC18F4550 PWM Example in CCS PICC

Overview

Creating a varied analog voltage output from an MCU require an analog voltage generator, PWM (pulse width modulation). Making a analog voltage PWM to work, the user needs to know about all relevant register configurations to set the frequency and duty cycle of PWM signal.

x2

x1.5

x1

x0.5

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However, in a high level embedded language, creating a PWM signal output doesn't need a deep level of low level hardware/register configuration. With a few C functions, the PWM signal output from any MCU could be created in a few minutes.

CCS PICC Basic Pulse Width Modulation Programming

Without using any technical detail of PWM software setting, we can create a PWM output from scratch with this compiler. In this introductory example, I use only a few C code to program the PWM.

1. #use PWM directive
2. pwm_set_duty_percent()

The directive #use PWM has many options, but I list a few commonly use options of this.

• CCPx or PWMx - Select a CCP/PWM module
• FREQUENCY=x - Set the frequency of PWM signal
• PERIOD=x - Set the period of PWM signal
• DUTY=x - The default duty cycle is 50% if it's not set.

For more details about this directive, check the compiler manual.

The pwm_set_duty_percent specifies the duty cycle of PWM output signal. The syntax is pwm_set_duty_percent(stream,value). Where stream is optional, and value is ranges from 0 to 1000. For example when value = 500, the PWM duty cycle is 50% and so on.

In this introductory example, I set a fixed frequency of PWM and a variable duty cycle. Duty cycle is adjusted by the variation of a POT. CCP1 is selected to make the PWM signal.

I adjust the POT to the MAX.

C Source Code

	#include <18F4550.h>
	#device ADC=10
	#fuses HS,PLL1,CPUDIV1
	#use delay(clock=20000000)
	#use PWM(CCP1,FREQUENCY=10K,DUTY=0)
	#define LCD_ENABLE_PIN PIN_B2
	#define LCD_RS_PIN PIN_B0
	#define LCD_RW_PIN PIN_B1
	#define LCD_DATA4 PIN_B4
	#define LCD_DATA5 PIN_B5
	#define LCD_DATA6 PIN_B6
	#define LCD_DATA7 PIN_B7
	#include<lcd.c>
	void adcSetUp(void){
	set_tris_a(0x01);
	//Set RA0 To Analog
	setup_adc_ports(AN0);
	//Select ADC internal RC Clock
	setup_adc(ADC_CLOCK_INTERNAL);
	//Select channel 0 for conversion
	}
	void main(void){
	unsigned long temp;
	lcd_init();
	adcSetUp();
	lcd_gotoxy(1,1);
	printf(LCD_PUTC,"PWM EXAMPLE");
	while(1){
	/*Set PWM Duty Cycle*/
	set_adc_channel(0);
	delay_ms(1);
	temp=read_adc();
	while(!adc_done());
	/*Convert from 1024 to 1000*/
	temp=(temp*1000.0)/1024;
	pwm_set_duty_percent(temp);
	lcd_gotoXy(1,2);
	printf(LCD_PUTC,"Duty Cycle %0.2f ",(float)(temp/10.0));
	delay_ms(10);
	}
	}

view raw pwm_example_1.c hosted with ❤ by GitHub

Schematic 

Schematic Diagram

Click here to download this example in zip file.