PIC16f870 PWM module not working(Assembly Code)

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Cantafford2

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Hey,

I'm trying to set up the CCP1CON module of the PIC16f870 microcontroller in PWM mode. I wrote this simple code that's supposed to send a 100% duty cycle on the CCP1CON(RC2) pin. I have attached a dc motor interfaced with a L293D driver to test the duty cycle's value. I have calculated the values for the registers using this PWM calculator:

https://www.micro-examples.com/public/microex-navig/doc/097-pwm-calculator.html

This is the code:
Code: 
#include "p16F870.inc"

; CONFIG
; __config 0xFF3A
__CONFIG _FOSC_HS & _WDTE_OFF & _PWRTE_OFF & _CP_OFF & _BOREN_OFF & _LVP_OFF & _CPD_OFF & _WRT_ALL

cblock 20h
  d1
  d2
  d3
endc


RES_VECT  CODE    0x0000            ; processor reset vector
    GOTO    START                   ; go to beginning of program

; TODO ADD INTERRUPTS HERE IF USED

MAIN_PROG CODE                      ; let linker place main program

START
  
    bsf 03h, 5 ; select bank1
    bcf 03h, 6
    movlw b'00000000' ; PORTB made as output
    movwf 86h
    call _pwm_init
    movlw h'01' ;direction assigned for the motor
    movwf 06h
  
loop ; loop forever
  
  
  
  
goto loop

  
_delay_1s
        movlw    0x2D
    movwf    d1
    movlw    0xE7
    movwf    d2
    movlw    0x0B
    movwf    d3
_delay_1s_0
    decfsz    d1, f
    goto    $+2
    decfsz    d2, f
    goto    $+2
    decfsz    d3, f
    goto    _delay_1s_0
        return
  
_pwm_init
    bcf 87h, 2 ;make RC2 bit an output
    movlw b'11001111'
    movwf 92h   ;PR2
    bcf 03h, 5 ; select bank0
         bcf 03h, 6
    movlw b'00000111'
    movwf 12h   ;T2CON
    movlw b'01100111'
    movwf 15h   ;CCPR1L
    movlw b'00111100'
    movwf 17h   ;CCP1CON
    return
    END

My CCP1CON(RC2) pin won't initialise. It stays in 0 logic no matter what duty cycle I send. What am I missing? I calculated a pwm frequency of 1.5khz and a duty cycle of 100%

This is a screenshot of the schematic in Proteus Simulator.
https://i64.tinypic.com/1tmwqb.png
 

You make the code difficult to follow!

Tip 1:
as you seem to be using Microchip's assembler, use the banksel macro and defined names to select the bank/register/bit you want to use. For example, change:
Code: 
        bsf 03h, 5 ; select bank1
    bcf 03h, 6
    movlw b'00000000' ; PORTB made as output
    movwf 86h
to
Code: 
 banksel TRISB
movlw 0
movwf TRISB
note that 'clrf TRISB' is easier!

Tip 2:
Avoid using '$' as a destination, it isn't portable to other PIC families.
Instead, add a label and 'goto' it instead.

Incidentally, 100% PWM means constantly ON! I suspect the simulator doesn't show that properly.

Brian.
 

Hey. Thanks for answering. The simulator shows 100% duty cycle fine. Worked for several other projects. Also I have tried different duty cycles to no avail.
About how the code looks well I will re-write it in the form that you said and post it here after .
 

What about MCLR ? Is it enabled or disabled ? If enabled then you need to pull it up to 5V using 10k resistor.
 

What about MCLR ? Is it enabled or disabled ? If enabled then you need to pull it up to 5V using 10k resistor.
Click to expand...

The schematic shows it has a 10K pull-up to +5V and the 16F870 does not have configurable reset.

Brian.
 

The simulator shows 100% duty cycle fine.
Click to expand...

If you are just simulating in Proteus then it will not work. It works fine for 100% duty cycle but not for others. I think you need a Core i7 system to simulate it in real time else it will just appear as flickering LED. Proteus can't simulate the LED model so fast. Test it in hardware.
 

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