16F88 PWM and A/D conversion

[williB]

Oh and Nigel , initialize is spelled with a Z.
lol NOT AN S

can anyone link me to the errata sheet for the midrange reference manual

 

[williB]

does anyone know if this code works??
its from the microchip midrange manual..
its not working for me..
the pwm output pin does nothing.. not a blip and certainly no pwm..??..

CLRF CCP1CON ; CCP Module is off 
CLRF TMR2 ; Clear Timer2 
MOVLW 0x7F ; 
MOVWF PR2 ; 
MOVLW 0x1F ; 
MOVWF CCPR1L ; Duty Cycle is 25% of PWM Period 
CLRF INTCON ; Disable interrupts and clear T0IF 
BSF STATUS, RP0 ; Bank1 
BCF TRISC, PWM1 ; Make pin output 
CLRF PIE1 ; Disable peripheral interrupts 
BCF STATUS, RP0 ; Bank0 
CLRF PIR1 ; Clear peripheral interrupts Flags 
MOVLW 0x2C ; PWM mode, 2 LSbs of Duty cycle = 10 
MOVWF CCP1CON ; 
BSF T2CON, TMR2ON ; Timer2 starts to increment 
; 
; The CCP1 interrupt is disabled, 
; do polling on the TMR2 Interrupt flag bit 
; 
PWM_Period_Match 
BTFSS PIR1, TMR2IF 
GOTO PWM_Period_Match 
; 
; Update this PWM period and the following PWM Duty cycle 
; 
BCF PIR1, TMR2IF

just thought i'd ask again

 

[Mike - K8LH]

Hi Willi,

In that code you just posted, isn't PR2 in Bank 1 Sir? Did I miss the bank switch in your code?

Regards, Mike

 

[williB]

hmmm you are correct .. :lol:

 

[Mike - K8LH]

Hi Willi,

Which PIC are you using? 16F88 or 16F684?

Also, shouldn't you be turning on TMR2 with a bsf T2CON,TMR2ON instruction somewhere? Oops, I see it... Excuse me...

Regards, Mike

 

[williB]

Sorry i know its hard to follow but i am using the 16F628..
i just redid the .asm file ..
assembled it ..
reprogrammed the 628 .....
still nothing..damn

 

[Mike - K8LH]

Hi Willi,

Yep, that banking stuff gets me all the time (grin)... It may seem silly, but I use something like this to keep track of banking on the 14-bit core PICs;

;
        CLRF    CCP1CON         ; CCP Module is off      |B0
        CLRF    TMR2            ; Clear Timer2           |B0
        MOVLW   0x7F            ;                        |B0
        MOVWF   PR2             ;                        |B1 <-- oops!
        MOVLW   0x1F            ; duty cycle is 25%      |B0
        MOVWF   CCPR1L          ; of PWM Period          |B0
        CLRF    INTCON          ; Disable interrupts     |B0
        BSF     STATUS, RP0     ; Bank1                  |B1
        BCF     TRISC, PWM1     ; Make pin output        |B1
        CLRF    PIE1            ; Disable peripheral inte|B1
        BCF     STATUS, RP0     ; Bank0                  |B0
;

Regards, Mike

 

[Mike - K8LH]

i am using the 16F628..

I set up PWM on a 16F877 a while back... Let me dig up that code... Perhaps it'll be close to what we would need for a '628...

Regards, Mike

 

[williB]

cool thanks..!!
let me ask a dumb question ..
is the code as written able to run just once or should i loop through it..?

 

[Mike - K8LH]

Hi Willi,

Sorry, just got back from an errand... I'll look for that code now... IIRC, I used Hyperterminal (which I do a lot) and I repeatedly pressed the left and right arrow keys to ramp up or ramp down the speed of a 12-vdc computer fan... A single PWM output was driving a TIP122 which was driving the fan... I was just experimenting... I haven't done anything tangible with PWM... Sorry...

Regards, Mike

 

[williB]

Thats VERY tangible..

 

[williB]

Nothing??

 

[Mike - K8LH]

Hi Willi,

I can't find that code... Bummer!!!

So, I dug out the Data Sheet and threw this code together... Let me burn it into a '628A and throw it into a board along with an LED... Oops! Just realized the Data Sheet is for a '628 and not a '628A so I better check for the differences... Hang in there... Or, feel free to disect this code and compare it to yours...

Regards, Mike

;******************************************************************

        org	0x0000

RESET	clrf    STATUS          ;                                 |B0
        clrf    PORTA           ; clear Port A data latches       |B0
        clrf    PORTB           ; clear Port B data latches       |B0
        movlw   h'07'           ;                                 |B0
        movwf   CMCON           ; turn comparator off             |B0
        bsf     STATUS,RP0      ; select bank 1                   |B1
        clrf    TRISA           ; port A all outputs              |B1
        clrf    TRISB           ; port B all outputs              |B1
        bcf     STATUS,RP0      ; select bank 0                   |B0
;
;  setup PWM (looks like CCPR1L uses Tosc while PR2 uses Tcyc)
;
        clrf    T2CON           ; TMR2 prescale:1                 |B0
        movlw   d'100'          ; same as (100*4)>>2              |B0
        movwf   CCPR1L          ; 100 usecs, 50% duty cycle?      |B0
        bsf     STATUS,RP0      ; select bank 1                   |B1
        movlw   d'200'-1        ; 200 1.0 usec 'ticks'            |B1
        movwf   PR2             ; Period=200 usecs, Freq=5.0 KHz  |B1
        bcf     STATUS,RP0      ; select bank 0                   |B0
        movlw   b'00001100'     ;                                 |B0
        movwf   CCP1CON         ; put CCP module in PWM mode      |B0
        bsf     T2CON,TMR2ON    ; turn on TMR2                    |B0
;
;  now test to see if the LED on RB3 is glowing at 50% brightness
;
LOOP    goto    LOOP            ; loop indefinately               |B0
;
;***************************************************************

 

[williB]

the code should work on a 628A
lemmy try it..

 

[Mike - K8LH]

Yep, no changes were required... And, it works... I tried 50%, 100%, 25%, and 10% duty cycles and I could see a difference, though I'm not sure I'm calculating duty cycle correctly...

Is this enough of an example to get yours going?

Regards, Mike

<added>

I should mention the '628A was running INTOSC at 4-MHz...

 

[williB]

i'm gonna try it , thanks !!

 

[williB]

how do i change the duty cycle??

 

[williB]

movlw d'100'
change this right ?

 

[williB]

i changed movlw d'100'
to 50
and got 25% duty cycle
it was fifty ..
this is soooo cool...
thanks :wink:

 

[Mike - K8LH]

Yeah, change the value in CCPR1L to any value between d'000' and d'200' and you'll effect changes in 0.5% increments...

If you change PR2 to d'100' then you'll have a 1 to 1 relationship with the CCPR1L register... CCPR1L values of d'001' through d'100' will be 1.0% increments (period=100-usecs, freq=10-KHz)...

If you change PR2 to d'255' then you'll have a CCPR1L range of d'000' to d'255', which would be a perfect match for the high 8-bits of the ADC module and a potentiometer...

Good luck... Have fun... Regards, Mike