16f877 generate pwm according 2 analog input

[madxice]

Hello everybody,

I am trying to make buck converter and control it with 16f877. The logic is simple. If the output voltage of the buck is higher than reference voltage the pwm duty cycle will decrease, if the output voltage is lower than the reference the duty cycle will increase. It seems very simple, but I couldn't be able to write the program I write but i doesn't work. I am new at pic programming. Help me please!!!

My crystal is 20MHz.

And it gives an error " ADC conversion clock period (1e-7) is possible invalid for device clock frequency" in proteus simulation.

 

  DEFINE OSC 20
 DEFINE ADC_BITS  8    
 DEFINE ADC_SAMPLES 50

 TRISA=%00000011 
 TRISB=00 
 TRISC=00 
 TRISD=00 
 TRISE=00


Reference var byte
Voltage var byte

CCP1CON=%000011100
CCP2CON=%000011100
T2CON=%00000101    'timer 2 on, 1:1 postscale, 1:4 prescale
PR2= 49            
CCPR1L=%00011001


get_reference:
ADCON1=%00000000
' Set LEFT Justification
' Enable ALL ADC's (using PIC16F87x as example)
ADCON0=%11000001

' Set ADC Channel 0 (RA0/AN0)
' Enable ADC Module
PauseUS 50
' 50uS Pause to allow sampling Capacitor to charge
ADCON0.1=1
' Start Conversion
While ADCON0.1=1:Wend
' Wait for conversion to complete
Reference=ADRESH
' Read 8-bit Result
return

get_voltage:                  
ADCON0=%11001001
' Set Fosc/32
' Set ADC Channel 1 (RA1/AN1)
' Enable ADC Module
PauseUS 50
ADCON0.1=1
While ADCON0.1=1:Wend
Voltage=ADRESH
return

azalt:
CCPR1L=CCPR1L-1
return

arttir:
CCPR1L=CCPR1L+1
return

sabit:
CCPR1L=CCPR1L
return

main_loop:
Gosub get_Reference ' Get reference value
Gosub get_voltage ' Get voltage value
if  Reference>Voltage    then azalt
if  Reference< Voltage    then arttir
IF Reference=Voltage   then sabit
goto main_loop         ' Do it forever

end