Code :

---

program variation;

var i, j : byte;

begin
i := 0; j := 0;
TRISB:=0;
PORTB := $FF; // Initialize PORTC
Pwm_Init(5000); // Initialize PWM module, freq = 5kHz.
Pwm_Start; // Start PWM

while true do
begin
for i := 0 to 20 do Delay_ms(100);
Inc(j);
Pwm_Change_Duty(j); // Change duty ratio
end;
end.