#include <p18f1320.h>
#pragma config WDT = OFF, LVP = OFF, OSC = INTIO2

#define ServoPin LATBbits.LATB3
#define ServoTris TRISBbits.TRISB3

void ccp1_isr();                    

volatile int ServoPos;          //used to hold the servo position

#pragma code low_vector=0x18    //setup the ISR vector
void low_interrupt (){
  _asm GOTO ccp1_isr _endasm    //jump to interrupt handler
}
#pragma code

#pragma interruptlow ccp1_isr   //the ISR
void ccp1_isr(){
    if(ServoPin==1){            //will be 1 if we are at end of pulse
        ServoPin=0;             //turn off servo output
        CCPR1=20000-ServoPos;   //Off time = 20mS - Servo Time
    }
    else{
        ServoPin=1;             //turn on servo output
        CCPR1=ServoPos;         //On time 
    }
    PIR1bits.CCP1IF=0;          //clear int flag
}
#pragma code

void main(){
    OSCCON=0x70;                //Osc=8MHz
    ADCON0=0b00000101;          //A2D on and select AN1
    ADCON1=0x7d;                //A1 = analogue
    ADCON2=0b10110101;          //Right justify - Fosc/16
    ServoTris=0;                //make bit 0 output
    ServoPin=0;                 //Servo output off
    CCP1CON=0b00001011;         //Special event trigger
    T1CON=0b10010001;           //Timer 1 on with Pre=2
    ServoPos=1500;              //set servo to mid position
    CCPR1=ServoPos;             //set CCP initial value   
    PIE1bits.CCP1IE=1;          //enable CCP1 interrupt
    INTCONbits.PEIE=1;          //enable peripheral interrupts
    INTCONbits.GIE=1;           //enable glogal interrupts
    INTCON2bits.RBPU=0;         //enable port b week pullups
    while(1){                   //loop forever
    static char Mode=0;             //0 = use ADC, 1=fixed pos
    static char Keys;               //holds previous key values
    char OldKeys,Edges;             //local variables
        while(!ServoPin);           //Wait for start of servo pulse
        while(ServoPin);            //wait for end - makes for good debounce
        OldKeys=Keys;               //make a copy of keys
        Keys=PORTB&0b00100101;      //get switch state
        Keys^=0b00100101;           //make pressed keys = 1
        if(Keys==0b00100101)        //all 3 pressed?
            Mode=0;                 //yes, set to use ADC input
        Edges=(Keys^OldKeys);       //keep only keys that have changed
        Edges&=Keys;                //keep only new key presses - not key releases
        if(Mode==0){                //are we using the pot?
            ADCON0bits.GO=1;        //yes, start conversion
            while(ADCON0bits.GO);   //Wait for it to complete
            ServoPos=ADRES+1000;    //Pos will be 1mS to 2.023mS
        }
        if(Edges!=0)                //any key pressed
            Mode=1;                 //switch to fixed mode
        if(Edges==0b00000001)       //Key 1 pressed
            ServoPos=1000;          //set servo fully left
        if(Edges==0b00000100)       //key 2?
            ServoPos=1500;          //set center
        if(Edges==0b00100000)       //key 3?
            ServoPos=2000;          //set fully right
    }
}