Use MPLAB IDE and use the assembly code which is provided below to modify and change the duty cycle to get the below waveforms . The code: ;;;;;;; P1 for QwikFlash board ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; ; Use 10 MHz crystal frequency. ; Use Timer0 for ten millisecond looptime. ; Blink "Alive" LED every two and a half seconds. ; Toggle C2 output every ten milliseconds for measuring looptime precisely. ; ;;;;;;; Program hierarchy ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; ; Mainline ; Initial ; BlinkAlive ; LoopTime ; ;;;;;;; Assembler directives ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; list P=PIC18F4520, F=INHX32, C=160, N=0, ST=OFF, MM=OFF, R=DEC, X=ON #include __CONFIG _CONFIG1H, _OSC_HS_1H ;HS oscillator __CONFIG _CONFIG2L, _PWRT_ON_2L & _BOREN_ON_2L & _BORV_2_2L ;Reset __CONFIG _CONFIG2H, _WDT_OFF_2H ;Watchdog timer disabled __CONFIG _CONFIG3H, _CCP2MX_PORTC_3H ;CCP2 to RC1 (rather than to RB3) __CONFIG _CONFIG4L, _LVP_OFF_4L & _XINST_OFF_4L ;RB5 enabled for I/O errorlevel -314, -315 ;Ignore lfsr messages ;;;;;;; Variables ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; cblock 0x000 ;Beginning of Access RAM TMR0LCOPY ;Copy of sixteen-bit Timer0 used by LoopTime TMR0HCOPY INTCONCOPY ;Copy of INTCON for LoopTime subroutine ALIVECNT ;Counter for blinking "Alive" LED endc ;;;;;;; Macro definitions ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; MOVLF macro literal,dest movlw literal ;move literal value to WREG movwf dest ;move WREG to f= dest, which is specified by user endm ;;;;;;; Vectors ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; org 0x0000 ;Reset vector, READ Section 5.7 nop goto Mainline ;goes to Mainline; thus skipping the interrupts below org 0x0008 ;High priority interrupt vector goto $ ;Trap org 0x0018 ;Low priority interrupt vector goto $ ;Trap ;;;;;;; Mainline program ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Mainline rcall Initial ;Initialize everything Loop btg PORTC,RC4 ;Toggle pin, to support measuring loop time rcall BlinkAlive ;Blink "Alive" LED rcall LoopTime ;Make looptime be ten milliseconds bra Loop ;;;;;;; Initial subroutine ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; ; This subroutine performs all initializations of variables and registers. Initial MOVLF B'10001110',ADCON1 ;Enable PORTA & PORTE digital I/O pins MOVLF B'11100001',TRISA ;Set I/O for PORTA 0 = output, 1 = input MOVLF B'11011100',TRISB ;Set I/O for PORTB MOVLF B'11010000',TRISC ;Set I/0 for PORTC MOVLF B'00001111',TRISD ;Set I/O for PORTD MOVLF B'00000000',TRISE ;Set I/O for PORTE MOVLF B'10001000',T0CON ;Set up Timer0 for a looptime of 10 ms; bit7=1 enables timer; bit3=1 bypass prescaler MOVLF B'00010000',PORTA ;Turn off all four LEDs driven from PORTA ; See pin diagrams of Page 5 in DataSheet MOVLF B'11111111',TMR0H ;ADDED by AC MOVLF B'00000000',TMR0L ;ADDED by AC MOVLF B'00000100',ALIVECNT ;ADDED by AC return ;;;;;;; LoopTime subroutine ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; ; This subroutine waits for Timer0 to complete its ten millisecond count ; sequence. It does so by waiting for sixteen-bit Timer0 to roll over. To obtain ; a period of precisely 10000/0.4 = 25000 clock periods, it needs to remove ; 65536-25000 or 40536 counts from the sixteen-bit count sequence. The ; algorithm below first copies Timer0 to RAM, adds "Bignum" to the copy ,and ; then writes the result back to Timer0. It actually needs to add somewhat more ; counts to Timer0 than 40536. The extra number of 12+2 counts added into ; "Bignum" makes the precise correction. Bignum equ 65536-1250+12+2 LoopTime btfss INTCON,TMR0IF ;Wait until ten milliseconds are up OR check if bit TMR0IF of INTCON == 1, skip next line if true bra LoopTime movff INTCON,INTCONCOPY ;Disable all interrupts to CPU bcf INTCON,GIEH movff TMR0L,TMR0LCOPY ;Read 16-bit counter at this moment movff TMR0H,TMR0HCOPY movlw low Bignum addwf TMR0LCOPY,F movlw high Bignum addwfc TMR0HCOPY,F movff TMR0HCOPY,TMR0H movff TMR0LCOPY,TMR0L ;Write 16-bit counter at this moment movf INTCONCOPY,W ;Restore GIEH interrupt enable bit andlw B'10000000' iorwf INTCON,F bcf INTCON,TMR0IF ;Clear Timer0 flag return ;;;;;;; BlinkAlive subroutine ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; ; This subroutine briefly blinks the LED next to the PIC every two-and-a-half ; seconds. BlinkAlive ; bsf PORTA,RA4 ;Turn off LED ; decf ALIVECNT,F ;Decrement loop counter and return if not zero ; bnz BAend ; MOVLF 4,ALIVECNT ;Reinitialize BLNKCNT ; bcf PORTA,RA4 ;Turn on LED for ten milliseconds every 2.5 sec bsf PORTC, RC0 rcall LoopTime bcf PORTC, RC0 bsf PORTC, RC1 rcall LoopTime bcf PORTC, RC1 bsf PORTC, RC2 rcall LoopTime bcf PORTC, RC2 bsf PORTC, RC3 rcall LoopTime bcf PORTC, RC3 BAend return end ;Task1 ; bsf PORTC, RCO ; rcall LoopTime ; ; bcf PORTC, RC0 ; bsf PORTC, RC1 ; rcall LoopTime ; ;return