Module CCP1 as a PWM signal generator

This example illustrates the use of CCP1 module in PWM mode. To make it more interesting, the width of P1A output pulses (PORTC,2) may be changed using pushbuttons symbolically marked as ‘DARK’ and ‘BRIGHT’, while the set width is visible as a binary combination on PORTB. The operation of this module is under control of the procedures belonging to the specialized PWM Library. Three of them are used here:

1. PWM1_init has the prototype: sub procedure PWM1_Init(const freq as longint) Parameter freq sets the frequency of PWM signal expressed in herz. In this example it is 5 KHz.
2. PWM1_Start has the prototype: sub procedure PWM1_Start()
3. PWM1_Set_Duty has the prototype: sub procedure PWM1_Set_Duty(dim duty_ratio as byte) Parameter duty_ratio sets pulse duration in a pulse sequence.

The PWM library also contains the PWM_Stop procedure used to disable this mode. Its prototype is: sub procedure PWM1_Stop()

' Header ******************************************************
program example_6 ' Program name
dim current_duty, old_duty, oldstate as byte ' Define variables current_duty
 ' old_duty and oldstate
main: ' Start of program
ANSEL = 0 ' All I/O pins are configured as digital
ANSELH = 0
PORTA = 255 ' PORTA initial state
TRISA = 255 ' All PORTA pins are configured as inputs
PORTB = 0 ' Initial state of PORTB
TRISB = 0 ' All PORTB pins are configured as outputs
PORTC = 0 ' PORTC initial state
TRISC = 0 ' All PORTC pins are configured as outputs
PWM1_Init(5000) ' PWM module initialization (5 KHz)
current_duty = 16 ' Initial value of variable current_duty
old_duty = 0 ' Reset variable old_duty
PWM1_Start() ' Start PWM1 module

while 1 ' Endless loop
 if oldstate and Button(PORTA, 0,1,1) then ' If the button connected to RA0 is pressed
 current_duty = current_duty + 1 ' increment variable current_duty
 if Button(PORTA, 0, 1, 1) then
 oldstate = 255
 end if
 end if
 
 if oldstate and Button(PORTA, 1,1,1) then ' If the button connected to RA1 is pressed
 current_duty = current_duty - 1 ' decrement value current_duty
 if Button(PORTA, 1, 1, 1) then
 oldstate = 255
 end if
 end if
 
 if old_duty <> current_duty then ' If current_duty and old_duty are not
 PWM1_Set_Duty(current_duty) ' equal set PWM to a new value,
 old_duty = current_duty ' save the new value
 PORTB = old_duty ' and show it on PORTB
 end if
 
 Delay_ms(200) ' 200mS delay
wend

end. ' End of program

In order to make this example work properly, it is necessary to check the following libraries in the Library Manager prior to compiling:

• PWM
• Button