While debugging the code for the 12F683 servo slowdown project I had the need for a debugger to find a weird problem. But you can't debug a 12F683 unless you spend $35+ for Microchip's debuggable 14-pin version of the chip. So I ported the code to the 18F1320 on the Junebug.

I tried several different methods before settling on something that would work on the 12F683 as well as the 18F1320. And I cured my weird problem completely. Works very well.

The Olimex ARM7 board outputs a servo pulse-train which varies according to the position of the potentiometer you can see me turning in the photo (right). I connect that output to RB3 on the 18F1320. The breadboard still has the 12F683 circuit on it, but that's not connected. I'm only using the servo connector for convenience. Both circuit boards and the breadboard have common grounds, and the Junebug is supplying 5V for the breadboard/servo. I'm using RB4 on the 18F1320 as the servo output. VR1 on the Junebug sets the servo speed. If VR1's value is <5 then the servo runs at full speed.

Here's the code:

/*-----------------------------------------------------------*/
/*PIC 18F1320                                                */
/*Measures servo input pulses on RB3 and outputs matching    */
/*pulse-train on RB4, but slowed by the amount selected      */
/*by pot value. If pot value is <5 then servo runs at full   */
/*speed.                                                     */
/*To change setting either stop input pulse-train or briefly */
/*kill the power to the 18F1320.                             */
/*-----------------------------------------------------------*/

#include <system.h>
#pragma	CLOCK_FREQ	8000000
#pragma DATA    _CONFIG1H, _INTIO2_OSC_1H
#pragma DATA    _CONFIG2H, _WDT_OFF_2H
#pragma DATA    _CONFIG3H, _MCLRE_ON_3H
#pragma DATA    _CONFIG4L, _LVP_OFF_4L

unsigned int loop1(void);
void movedown(void);
void moveup(void);
unsigned int straight_thru(void);
unsigned int pulsin(void);
void pulsout(int);

unsigned int pwinprev,pwout,pwinerr;
volatile unsigned int pwin,start,end;
unsigned char delay,skip;
volatile unsigned char flag;

void main()
{
    osccon = 0x72;          //set int osc to 8MHz
    trisa = 0b00000010;     //set data directions
    trisb = 0b00001000;
    adcon0 = 0b00000100;	//VREF = AVDD/AVSS
    adcon1 = 0b01111101;    //AN1 is analog, the rest digital
    adcon2 = 0b00011101;    //left justified,6TAD,FOSC/16
    ccp1con = 0b00000101;   //capture rising edge
    t1con = 0b00010001;     //Timer1 enable, pre=2
    rcon.IPEN = 0;          //disable priority interrupts
    pie1.CCP1IE = 0;        //disable ccp1 interrupt
    pie1.TMR1IE = 0;        //disable timer1 overflow interrupt
    intcon.PEIE = 1;        //enable peripheral interrupts
    intcon.GIE = 1;         //disable global interrupts

    while(1){
        do{
            skip = 0;
            pulsout(1000);          //sorta center servo
            delay_ms(2);
            adcon0.ADON = 1;        //enable A/D on AN1
            adcon0.GO = 1;          //start conversion
            while(adcon0.DONE);     //wait for conversion to complete
            delay = adresh;         //get 8-bit A/D value
            adcon0.ADON = 0;        //disable A/D on AN1
            pulsin();               //read incoming pulse width
        }while(pwin == 0);
        pwinprev = pwin;
        if(delay < 5)
            straight_thru();
        delay = delay / 21;
        pwout = pwin;
        loop1();
    }    
}

unsigned int loop1(void)
{
    while(1){
        pwinprev = pwin;
        pulsin();
        if(pwin == 0)
            return 0;
        pwinerr = pwin - pwout;
        if(pwinerr < 8 || pwinerr > 0xfff8)
            pulsout(pwout);                 //stay put
        else if(pwout < pwin)
            moveup();
        else if(pwout > pwin)
            movedown();
    }        
}

void movedown(void)
{
    if(skip < delay){
        skip += 1;
    }
    else{
        skip = 0;
        pwout -= 12;
    }
    pulsout(pwout);
}

void moveup(void)
{
    if(skip < delay){
        skip += 1;
    }
    else{
        skip = 0;
        pwout += 12;
    }
    pulsout(pwout);
}

unsigned int straight_thru(void)
{
    while(1){
        pulsin();
        if(pwin == 0)
            return 0;
        pwinerr = pwin - pwinprev;
        if((pwinerr < 8) || (pwinerr > 0xfff8)){
            pulsout(pwinprev);
        }    
        else{
            pulsout(pwin);
            pwinprev = pwin;
        }
    }    
}

void pulsout(int width)
{
    unsigned int temp;
    t1con.TMR1ON = 0;       //timer1 disable
    temp = 7 - width;       //preload timer1
    HIBYTE(tmr1h,temp);
    LOBYTE(tmr1l,temp);
    pie1.TMR1IE = 1;        //enable timer1 overflow interrupt
    t1con.TMR1ON = 1;       //timer1 enable
    portb.RB4 = 1;          //start servo pulse
}

unsigned int pulsin(void)
{
    int f;
    flag = 0;
    pie1.CCP1IE = 1;            //enable ccp1 interrupt
    for(f=0;f<3200;f++){        //wait for pulse measurement
        if(flag){               //if pulse measured then
            pie1.CCP1IE = 0;    //disable ccp1 interrupt
            return 0;           //and return
        }    
    }        
    pwin = 0;                   //but if no pulse then timeout
    pie1.CCP1IE = 0;            //disable ccp1 interrupt
}

void interrupt(void)
{
    if(pir1.CCP1IF){                    //timer1 capture interrupt
        if(portb.RB3){                  //rising edge detected
            start = ccpr1l;             //store start value
            start |= ccpr1h << 8;
            ccp1con = 0b00000100;       //set to capture falling edge
        }
        else{                           //falling edge detected
            end = ccpr1l;               //store end value
            end |= ccpr1h << 8;
            ccp1con = 0b00000101;       //set to capture rising edge
            flag = 1;
            if(end < start){
                pwin = (0xffff - start) + end;
            }    
            else{
                pwin = end - start;
            }    
        }
        pir1.CCP1IF = 0;                //clear interrupt flag
    }
    
    if(pir1.TMR1IF){                    //timer1 overflow interrupt
        portb.RB4 = 0;                  //end servo pulse
        pie1.TMR1IE = 0;                //disable timer1 overflow interrupt
        pir1.TMR1IF = 0;                //clear interrupt flag
    }
}