PIC 18F4520频率和变量问题

Question

我正在使用带有中断和计时器的程序进行倒计时： 我正在使用内部振荡器（带PLL的4MHz x 4）。

1）中断的频率与我想要达到的频率（1000 Hz）不一致。

2）如果我在char计数器中修改变量int counter变量，它就不起作用。

 #include <xc.h>
    #include "afficheur.h"

    #include "eeprom.h"
    #include <stdio.h>
    #include <string.h>
    #include "pause.h"
    #include "timer2.h"


    #define _XTAL_FREQ 16000000


    //unsigned int counter = 0; //work with bad frequency
    unsigned char counter = 0;      //doesn't work

    void interrupt isr2 (void) {            


      if (INTCONbits.TMR0IF == 1 )           
            {
    TMR0 = 6;
                INTCONbits.TMR0IF = 0;        

                ++counter;

            }
        }


    void timerCount(void)
    {
       LCD_init();
       initTimer();


        while(left_time!=0)
        {


            if (counter == 0)
            {
                display(left_time);

            }    

            updateTimer();
        }  
    }

    void  initTimer(void)
    {



                T0CON &= 11000011 ;      
                TMR0 = 6;

                  INTCON = 0;                    // clear the interrpt control register
                  INTCONbits.TMR0IE = 1;         // bit5 TMR0 Overflow Interrupt 
                  INTCONbits.TMR0IF = 0;        
                  INTCONbits.GIE = 1;            // bit7 global interrupt enable
    }

    void  updateTimer(void)
    {

        if (counter == 1000)  //1000 milliseconds => 1 second
        {

            counter = 0;
            left_time-=1;


        }


    }


    void  display(int time)
    {

        char str [20];

        char h_left [10];
        char m_left [10];
        char s_left [10];

        char compt [10];

        //time calculation
        sprintf(m_left, "%02d", time/60);
        sprintf(s_left, "%02d", time%60);   
        sprintf(h_left, "%02d", (time/60)/60);
        sprintf(m_left, "%02d", (time/60)%60);

        sprintf(compt,"%04d",counter);

            //**time display HH:MM:SS

        char *h_disp = h_left;
        char *m_disp = m_left;
        char *s_disp = s_left;
        char *compt_disp = compt;

        strcpy(str, h_disp);
        strcat(str, ":");
        strcat(str, m_disp);
        strcat(str, ":");

        strcat(str, s_disp);

        strcat(str, ":");
        strcat(str,compt_disp);

    //lcd rendering

        command(0xC3);
        LCD_write("Temps restant:");
        command(0x9A);
        LCD_write(str);
        //LCD_write(compt_disp);
        command(0xD4);
    }

我事先感谢你的帮助，

克里斯