Dear All,

I have loaded following program to the 16F877. I'm expecting a 5kHz PWM =
output duty according to the A/D input. But it only gives out 5kHz PWM =
output embedded in a 53Hz (approx.) 50% duty square signal. My xtal runs =
at 20MHz. I have tried shielding clock wire but to no good. Why is this?

Regards
Dilan Amarasinghe

ORG 0
; Initializing PWM Module

 BANKSEL PR2  ; Bank 1
 MOVLW 0xFF
 MOVWF PR2  ; PR2 =3D 256=20
 BCF TRISC, 2 ; CCP1 -> output
 BANKSEL CCPR1L  ; Bank 0
 MOVLW B'01111111' ; Duty =3D 127 (50%)
 MOVWF CCPR1L
 BSF CCP1CON, 5 ; 2 LSBs of CCP1
 BSF CCP1CON, 4
 BSF T2CON, 0 ; Prescale =3D 4
 BCF T2CON, 1
 BSF T2CON, 2 ; TMR2 ON
 BSF CCP1CON, 3
 BSF CCP1CON, 2 ; CCP1 -> PWM Mode

; Initializing ADC Module
=20
 BANKSEL ADCON1  ; Bank 1
 BCF ADCON1, PCFG3 ; AN0 =3D input channel
 BCF ADCON1, PCFG2 ;=20
 BCF ADCON1, PCFG1 ;=20
 BCF ADCON1, PCFG0 ;
 BCF ADCON1, ADFM ; Left justify the results

 BANKSEL ADCON0  ; Bank 0
 BCF ADCON0, CHS0 ; Cha. 0 =3D Analog i/p
 BCF ADCON0, CHS1 ;
 BCF ADCON0, CHS2 ;
 BSF ADCON0, ADCS1 ; Conv. clk =3D 32Tosc
 BCF ADCON0, ADCS0 ;
 BCF INTCON, GIE ; Disable all ints
 BANKSEL PIE1  ; Bank 1
 BCF PIE1, ADIE ; Disable ADC  int
 BANKSEL ADCON0
 BSF ADCON0, ADON ; Sets ADC -> ON

 BANKSEL TRISB  ; Bank 3
 CLRF TRISB  ; Set PORTB as output

; ADC Control and Looping


 BANKSEL ADCON0  ; Bank 0
loop BSF ADCON0, GO
poll NOP
 BTFSC ADCON0, GO
 GOTO poll
 MOVF ADRESH, W ; Move result to W
=20
 MOVF ADRESH, 1
 MOVWF CCPR1L  ; Adjust the PWM duty with Analog input
 BANKSEL PORTB  ; Bank 2
 MOVWF PORTB
 GOTO loop

 END

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