16F88 PWM and A/D conversion

Mike - K8LH · Jun 13, 2005

I'll check it out... Thanks...

Regards, Mike

<added>

I read that document last year... Thanks...

Mike - K8LH · Jun 13, 2005

Willi,

When you get past the programmer hurdle, would you let me know if you've got ADC code for the 'F88? I just found some old 'F88 ADC code...

This looks like setup code and a subroutine to perform an ADC reading but I'm going to have to read the Data Sheet to refresh my memory...

Code:

;
; setup ADC module for RA0 as an analog input, Fosc/32 conversion
; clock (20-Mhz), and internal Vdd/Vss Voltage Reference.
;
        bsf     STATUS,RP0      ; select Bank 1                   |B1
        movlw   b'00000001'     ;                                 |B1
        movwf   TRISA           ; set RA0 pin as input            |B1
        movlw   b'00000001'     ; set RA0/AN0 pin as analog and   |B1
        movwf   ANSEL           ; other 6 ANx pins as digital     |B1
        movlw   b'01000000'     ; ADSC2 clock source/2            |B1
        movwf   ADCON1          ; left justified, internal Vref   |B1
        bcf     STATUS,RP0      ; select Bank 0                   |B0
;       movlw   b'01000000'     ; Fosc/08, ch 0, ADC off ( 8-mhz) |B0
        movlw   b'10000000'     ; Fosc/32, ch 0, ADC off (20-mhz) |B0
        movwf   ADCON0          ;                                 |B0

Code:

;
; turn on the ADC module, take a reading, return with 8 most
; signigicant bits of reading in W
;
ADC     bsf     ADCON0,ADON     ; turn on AD module               |B0
        bcf     PIR1,ADIF       ; clear AD interrupt flag         |B0
        movlw   d'33'           ; use 33 (20 mhz) or 13 (8 mhz)   |B0
        movwf   TEMP            ;                                 |B0
ACQ     decfsz  TEMP,F          ; wait 20 usec  to acquire        |B0
        goto    ACQ             ;                                 |B0
        bsf     ADCON0,GO_DONE  ; start conversion                |B0
ADX     btfsc   ADCON0,GO_DONE  ; conversion complete?            |B0
        goto    ADX             ; no, loop                        |B0
        movf    ADRESH,W        ; get result high byte            |B0
        bcf     ADCON0,ADON     ; turn off AD module              |B0
        return                  ;                                 |B0

Regards, Mike

williB · Jun 13, 2005

i stumbled across a circuit earlier today which showed RB3 connected to ground through a resistor .. do i need to do this , on the F88 when programming??
Except for the Chip Erase command & End Programming command the two (F628 & F88) are identical.. reason being ( which i forgot) they are programmed LSB first , when you look at the diagrams that way you can see they are identical..the F88 only uses 5 command bits where the F628 uses 6..

williB · Jun 13, 2005

crap !! i had it going earlier :evil:
but now its not cooperating ..

Jay.slovak · Jun 14, 2005

williB said:
i stumbled across a circuit earlier today which showed RB3 connected to ground through a resistor .. do i need to do this , on the F88 when programming??

The resistor is needed only when you use LVP - Low Voltage Programming. Because setting RB3 High will enter Programming mode (Regardless of MCLR). I highly recomend not use this mode, so in every program you write, simply disable LVP bit, so you can use RB3 as general purpose I/O. All new chips have LVP set on from the Factory, so that you can program them with LVP style programmer. :lol:

Someone Electro · Jun 14, 2005

The LVP once gave me headaces why it dosent work.Then i figured out that i have LVP on.

williB · Jun 14, 2005

SE the documentation says that you can use MCLR even when LVP is enabled..
i am almost there ..with the reprogramming..
i can alter a single location at will..
one step forward two steps back *sigh*

Jay.slovak · Jun 14, 2005

williB said:
SE the documentation says that you can use MCLR even when LVP is enabled..
i am almost there ..with the reprogramming..
i can alter a single location at will..
one step forward two steps back *sigh*

MCLR is always possible, LVP can be disabled..

williB · Jun 14, 2005

its done...
now to get the A to D working..

Someone Electro · Jun 14, 2005

You can also use MCRL to reset it and to program it.

LCP also resets wen the program is runing.

williB · Jun 14, 2005

Thanks SE.. , for your comment....

The programmer is doing a lot better , it just needed a little tweaking ..
the problem i noticed was that , it wasnt erasing properly but now its good..

Someone Electro · Jun 15, 2005

How did i help ? :|

williB · Jun 15, 2005

Is that better..

Someone Electro · Jun 15, 2005

What ???

williB · Jun 15, 2005

below i have combined the two modules ..
It works!! sort of , what it really does is turn the pwm on and off though(not what its supposed to do , which is to pass an A to D reading to the PWM module.)
just a little more tweeking should do it though..
i have moved part of the PWM module into the ADC module , where Mike put in a little delay..
i am not sure if this is causing the problem..

Code:

; setup ADC module for RA0 as an analog input, Fosc/32 conversion 
; clock (20-Mhz), and internal Vdd/Vss Voltage Reference. 
; 
        bsf     STATUS,RP0      ; select Bank 1                   |B1 
        movlw   b'00000001'     ;                                 |B1 
        movwf   TRISA           ; set RA0 pin as input            |B1 
        movlw   b'00000001'     ; set RA0/AN0 pin as analog and   |B1 
        movwf   ANSEL           ; other 6 ANx pins as digital     |B1 
        movlw   b'01000000'     ; ADSC2 clock source/2            |B1 
        movwf   ADCON1          ; left justified, internal Vref   |B1 
        bcf     STATUS,RP0      ; select Bank 0                   |B0 
;       movlw   b'01000000'     ; Fosc/08, ch 0, ADC off ( 8-mhz) |B0 
        movlw   b'10000000'     ; Fosc/32, ch 0, ADC off (20-mhz) |B0 
        movwf   ADCON0          ;                                 |B0 
 

 
; turn on the ADC module, take a reading, return with 8 most 
; signigicant bits of reading in W 
; 
ADC     bsf     ADCON0,ADON     ; turn on AD module               |B0 
        bcf     PIR1,ADIF       ; clear AD interrupt flag         |B0 
        movlw   d'33'           ; use 33 (20 mhz) or 13 (8 mhz)   |B0 
        movwf   TEMP            ;                                 |B0 
ACQ     decfsz  TEMP,F          ; wait 20 usec  to acquire        |B0 
        goto    ACQ             ;                                 |B0 
        bsf     ADCON0,GO_DONE  ; start conversion                |B0 
ADX     btfsc   ADCON0,GO_DONE  ; conversion complete?            |B0 
        goto    ADX             ; no, loop                        |B0 
        movf    ADRESH,W        ; get result high byte            |B0 
        bcf     ADCON0,ADON     ; turn off AD module              |B0 
        return                  ;                                 |B0 
;******************************************************************

Code:

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

Code:

        org   0x0000 

        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 
 
        movlw   b'00000001'     ;                                 |B1 
        movwf   TRISA           ; set RA0 pin as input            |B1 
        movlw   b'00000001'     ; set RA0/AN0 pin as analog and   |B1 
        movwf   ANSEL           ; other 6 ANx pins as digital     |B1 
        movlw   b'01000000'     ; ADSC2 clock source/2            |B1 
        movwf   ADCON1          ; left justified, internal Vref   |B1 
        bcf     STATUS,RP0      ; select Bank 0                   |B0 



        movlw   b'01000000'     ; Fosc/08, ch 0, ADC off ( 8-mhz) |B0 
        movwf   ADCON0          ;                                 |B0 
  
ADC     bsf     ADCON0,ADON     ; turn on AD module               |B0 
        bcf     PIR1,ADIF       ; clear AD interrupt flag         |B0 
       
        clrf    T2CON           ; TMR2 prescale:1                 |B0 
        movf	 RESULT,W      ;			   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 

        bsf     ADCON0,GO_DONE  ; start conversion                |B0 
ADX     btfsc   ADCON0,GO_DONE  ; conversion complete?            |B0 
        goto    ADX             ; no, loop                        |B0 
        movf    ADRESH,W        ; get result high byte            |B0 
        movwf   RESULT          ; store in temp register           B0
        bcf     ADCON0,ADON     ; turn off AD module              |B0

Mike - K8LH · Jun 15, 2005

Hi Willi,

Don't you want PR2 = 255 to match the 0-255 ADC reading? Are you using a 20-MHz crystal?

You probably want to read the ADC to get a 0-255 value and update CCPR1L with this new duty cycle value and repeat the process...

Leave ADC as a subroutine and use code similar to below, or, add a few lines at the end of the ADC routine to copy RESULT to CCPR1L and jump to ADC to repeat the process...

Good luck... Regards, Mike

Code:

        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'000'          ;                                 |B0
        movwf   CCPR1L          ; 00% duty cycle initially        |B0
        bsf     STATUS,RP0      ; select bank 1                   |B1
        movlw   d'255'-1        ; 255 200-nsec 'ticks'            |B1
        movwf   PR2             ; Period=255 (*200-nsecs)         |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 
;
; setup ADC module for RA0 as an analog input, Fosc/32 conversion
; clock (20-Mhz), and internal Vdd/Vss Voltage Reference.
;
        bsf     STATUS,RP0      ; select Bank 1                   |B1
        movlw   b'00000001'     ;                                 |B1
        movwf   TRISA           ; set RA0 pin as input            |B1
        movlw   b'00000001'     ; set RA0/AN0 pin as analog and   |B1
        movwf   ANSEL           ; other 6 ANx pins as digital     |B1
        movlw   b'01000000'     ; ADSC2 clock source/2            |B1
        movwf   ADCON1          ; left justified, internal Vref   |B1
        bcf     STATUS,RP0      ; select Bank 0                   |B0
;       movlw   b'01000000'     ; Fosc/08, ch 0, ADC off ( 8-mhz) |B0
        movlw   b'10000000'     ; Fosc/32, ch 0, ADC off (20-mhz) |B0
        movwf   ADCON0          ;                                 |B0
;
LOOP    call    ADC             ; read potentiometer (000..255)   |B0
        movwf   CCPR1L          ; update duty cycle               |B0
        goto    LOOP            ; loop forever                    |B0
; 
; turn on the ADC module, take a reading, return with 8 most
; signigicant bits of reading in W
;
ADC     bsf     ADCON0,ADON     ; turn on AD module               |B0
        bcf     PIR1,ADIF       ; clear AD interrupt flag         |B0
        movlw   d'33'           ; use 33 (20 mhz) or 13 (8 mhz)   |B0
        movwf   TEMP            ;                                 |B0
ACQ     decfsz  TEMP,F          ; wait 20 usec  to acquire        |B0
        goto    ACQ             ;                                 |B0
        bsf     ADCON0,GO_DONE  ; start conversion                |B0
ADX     btfsc   ADCON0,GO_DONE  ; conversion complete?            |B0
        goto    ADX             ; no, loop                        |B0
        movf    ADRESH,W        ; get result high byte            |B0
        bcf     ADCON0,ADON     ; turn off AD module              |B0
        return                  ;                                 |B0
;******************************************************************

williB · Jun 15, 2005

the main oscillator is 5.0688MHZ , but i can divide it by any power of two..

williB · Jun 15, 2005

i cant thank you enough really , thank you!!
as far as PR2 yes that is what i wanted to do , but i didnt know enough to know where to change it..

williB · Jun 15, 2005

i've been over and over the code , and i cant find anything wrong with it..
but since i am only running the chip at 333KHZ i am going to try clearing ADCON0 and ADCON1 in the ADC setup..and using a smaller loop value..
also why are you turning off the A/D module just to turn it back on after you get the result??
the PWM is working perfectly btw..but the adc section , not so much....

motion · Jun 15, 2005

I have used the PIC on a motor driver application in which the PWM duty cycle is a function of the ADC output and here are few tips I can give.

In your application as in mine, the A/D result is used to calculate the PWM duty. On the PWM module, the duty cycle can only change at timer2 overflow. In your case, it's at a 5Khz rate. This is regardless of how many times you load CCPR1L. Therefore, the 5Khz rate should dictate the rate you make A/D conversions and not the other way around (i.e., the A/D conversion rate dictating how fast you update CCPR1L).

A 5Khz A/D conversion rate is well within the limits of the PIC ADC. Selecting 8Tosc for Tad, the A/D conversion time is 12Tad or about 20usec. Since at 5Khz there is 200usec between A/D conversion intervals, there is 180usec of sampling time allowed.

All these is easily done if A/D conversion is synchronized with timer2 overflow. That is, you don't need to check the GO/DONE bit but instead poll the TMR2IF bit.

1. Poll the TMR2IF bit until it is set.
2. Clear TMR2IF bit.
3. Read the result from the previous A/D conversion and save result.
4. Use the A/D result to set the PWM duty.
5. Start a new conversion. This step can be done ahead of step 4.
6. Repeat step 1. While waiting for TMR2IF to be set in 200usec, the A/D conversion is completed after 20usec and the rest of the time is spent sampling.

BTW, you can also use interrupts here, using TMR2IF to initiate interrupt.

16F88 PWM and A/D conversion

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