How to connect xtal to T0CKI pin on PIC

[this]

Hi.
Problem: I need precise clock.
I have a 32768Hz xtal. I know I have to set prescaler to 1:128, and timer interrupt will be called on every overflow of 8bit timer(every 256 ticks), so I will get my precise 1s interrupt(32768/128/256 = 1).
This is clear for me, and I believe I have no problem with programming part.
I think the problem is with connecting xtal to T0CKI pin.(I tried few xtals, so it's not xtal fault)
I was trying to connect it like shown on 13 page of **broken link removed** but it's very unstable, sometimes it's way slower than 1s, sometimes it runs like crazy.
Could someone explain to me what is the proper way of connecting xtal to T0CKI? I would appreciate explanation of what and why.

Currently I have the circuit mentioned above(except i have two 2x22pF caps instead of 33 and var.)
I'm using PIC16F677
My code looks like this:

---

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TRISA = TRISB = TRISC = 0; //output only
    ANSEL = 0;// digital IO
    ANSELH = 0;// digital IO
        
    OPTION=0b10100110;
    //       1-------   pullups disabled
    //       -0------   
    //       --1-----   TMR0 source = transition on T0CKI
    //       ---1----   increment on L2H T0CKI
    //       ----0---   prescaller assigned to TMR0
    //       -----110   prescaller 1:128
    
    T0IE = 1;   //enable TMR0 interrupt
    GIE = 1;    // enable gloabl ints
    unsigned volatile char cnt=0;
    ......
    
    while(1)
    {
        lcd_clear();
        lcd_goto(0);//clear lcd
        display_on_lcd(cnt);//and display
        for(unsigned char i = 0; i<3;i++)//wait ~100ms
            __delay_ms(33);
    }
    
    .......
    
    
    void interrupt isr(void)
    {
        if(T0IF)//if timer interrupt
        {
            cnt++; //increase "stopwatch"
            T0IF = 0; //clear int. flag
        }   
    }

---

 

[microlab]

hi

please read the datasheet of 16F677,and check what's missing.

ml

 

[this]

Well, I did read it before I started, what did I miss? Some hint? page# or something
And small correction to my code - T0CKI is actually set as input, not output.

 

[microlab]

hi

TRISA = TRISB = TRISC = 0; //output only
ANSEL = 0;// digital IO
ANSELH = 0;// digital IO

OPTION=0b10100110;
// 1------- pullups disabled
// -0------
// --1----- TMR0 source = transition on T0CKI
// ---1---- increment on L2H T0CKI
// ----0--- prescaller assigned to TMR0
// -----110 prescaller 1:128

T0IE = 1; //enable TMR0 interrupt
GIE = 1; // enable gloabl ints
unsigned volatile char cnt=0;
bit test = 0; // display update when test == 0
......

while(1)
{
if(test == 0){
lcd_clear();
lcd_goto(0);//clear lcd
display_on_lcd(cnt);//and display
test = 1;
}
}

.......


void interrupt isr(void)
{
if(T0IF)//if timer interrupt
{
cnt++; //increase "stopwatch"
test = 0;// update display
T0IF = 0; //clear int. flag

}
}


you may change the crystal. may be this is the problem of the crystal too

regards

ml