Hello

I have changed to a PIC16F628 due to its simplicity and I have the following
code. Again, I am trying to simulate PWM signal out of RA0. I want to change
the duty cycle by changing the 4 bits input to the PIC and that is why I
have RB0 and RB1 for switch input. I am going round circles with this
one.(3.5 weeks) Please help and thanks.

Bathini

PS Simulating on MPLAB

; 
; 4-bit PWM for PIC16F628A or PIC16F627A
; 
; 
; RA0 - PWM out to motor
; RB0 - Switch input, increment duty cycle
; RB1 - Switch input, decrement duty cycle.
;
; Connect switches between I/O pin and Vss
;
; 
           	IFDEF __16F628A
	  #include "p16f628a.inc"     
	ENDIF

	IFDEF __16F627A
	  #include "p16f627a.inc"     
	ENDIF

              __CONFIG       _CP_OFF & _WDT_OFF & _BOREN_OFF & _PWRTE_ON &
_INTOSC_OSC_NOCLKOUT  & _MCLRE_ON & _LVP_OFF

               
              errorlevel -302             ; suppress banksel warning
messages
 
              
              cblock 0x70   ;0x70-0x7F common to all banks
               save_W       ;0.  save W during interupt
               save_Status  ;1.  save STATUS during interupt
               save_PCLATH  ;2.  save PCLATH
  	 portAcopy	;3.  working variable holds data to write to PORTA
	 period	;4.  period counter variable
	 duty	;5.  duty cycle loop counter variable
	 dutyReload	;6.  duty cycle variable
	 switches	;7.  switch state variable
  	 temp	;8.  temp variable used in switch functions

              endc
              
; Define port bit use
;-----------------------------
pb.pwm	equ	0            	; pwm output  
pb.swinc	equ	0	; duty cycle increment switch
pb.swdec	equ	1	; duty cycle decrement switch

; Define constants
;-----------------------------
Cperiod	equ	.15	; (0-15 = 16 levels or 4-bits)


             org           0x000         ;RESET VECTOR
             goto          startup      	;goto to startup code on reset
                      
; Initialise peripherals and registers at startup
;
startup     movlw         0x07
              movwf         CMCON         ;disable comparator
              
              movlw         0x00
              movwf         portAcopy
              call          output   
              
              banksel	OPTION_REG
              

              movlw         ~(1<<pb.pwm)	
              movwf         TRISA       
              
              movlw         b'11111111'   
              movwf         TRISB         

              ;all unused I/O lines on both ports are set to input and
should be tied to Vss

              
	movlw         b'00000000'   ;setup option register
              ;               ||||||||---- PS0 - Timer 0: Prescalar 1:2
              ;               |||||||----- PS1
              ;               ||||||------ PS2
              ;               |||||------- PSA -  Assign prescaler to Timer0
              ;               ||||-------- TOSE - LtoH edge
              ;               |||--------- TOCS - Timer0 uses IntClk
              ;               ||---------- INTEDG - falling edge RB0
              ;               |----------- RBPU - pull-ups enabled
              movwf         OPTION_REG

              banksel	PORTA

	movlw	Cperiod	; Initialise period 
	movwf	period
              
	movlw	.8	; set inital duty cycle to 50%
	movwf	dutyReload

              
; Run this code loop to generate PWM
;
loop	call	pwm	; compute PWM output
	call	output	; write to physical I/O port
	goto	loop	; repeat

; Compute the state of the PWM output bit
;
pwm	decfsz	period,F		; decrement period counter
	goto	pwm.cycle		; run duty cycle code until period times out

pwm.reload	movlw	Cperiod		; if one PWM period has elapsed, reload 
	movwf	period		; the period counter
	incf	dutyReload,W		; and duty cycle counter
	movwf	duty
	bsf	portAcopy, pb.pwm
	call	duty.switch	; test switches each once per period

pwm.cycle	decfsz	duty,F
	return
	bcf	portAcopy, pb.pwm
	return
              

; Write port copy variable to physical I/O Port
             
output      	movfw         portAcopy    	;load output var' into W
             	movwf         PORTA	;write to Port A
	return                   	;and return


              
; Test two switches and adjust duty cycle if switch pressed.

duty.switch	decfsz	temp,F
	return
	movfw	PORTB
	movwf	temp
	xorwf	switches,W
	andwf	switches,F
	btfsc	switches, pb.swinc
	call	duty.inc
	btfsc	switches, pb.swdec
	call	duty.dec
	movfw	temp
	movwf	switches
	clrf	temp
	return



duty.inc	incf	dutyReload,F
	movfw	dutyReload
	sublw	Cperiod
	skpc	dutyReload,4
	decf	dutyReload,F
	return

duty.dec	movf	dutyReload,F
	skpz
	decf	dutyReload,f
	return

             end





Bob

Thanks for  your reply. I have experimented with mplab and having problems
understanding it.I am 
currently using PIC simulator ide to see whether I can get the assembler
code working in PIC16F877A. 

Bathini



Bob Axtell wrote:
> 
> The simulator in MPLAB seems to work fine. Why not use that?
> 
> I routinely use PWM on the F88.
> 
> --Bob
> 
> On Fri, Jan 23, 2009 at 9:53 AM, bathini <wozamfethu@yahoo.es> wrote:
>> Hello Friends
>>
>> I am new to PICs and wanted to know how to simulate a PWM using 4bits as
>> input or a code I can learn from this? I want to simulate a PIC16F88, and
>> also do not know which simulation software to use. Thanks
>>
>> Bathini
>> --
> 
> 

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