Timer/Counter0 (ATmega168)

Last-modified: 2012-08-20 (Mon) 00:29:30 (2279d)

Timer0Test †

Timer/Counter0のオーバーフロー割り込みを使って、20ms周期のパルスを生成したサンプルプログラム。

//-----------------------------------------------------------------------------
//  ATmega168
//  Internal 8 MHz RC Osc.
//  (1/8M = 125 ns)
//-----------------------------------------------------------------------------

#include <avr/io.h>
#include <avr/interrupt.h>

#define TCNT0_InitVal   (256-80)    // 10ms (128usX80=10.24ms)

//-----------------------------------------------------------------------------
//  Timer/Counter0 Initialization
//-----------------------------------------------------------------------------
void initTimer0()
{
    TCCR0B = 0x00;          // Stop Timer/Counter0
    TCNT0 = TCNT0_InitVal;  // Initial Value of Timer/Counter0
    TIMSK0 = _BV(TOIE0);    // Timer/Counter0 Overflow Interrupt Enable
    TCCR0B = 0x05;          // Start Timer/Counter0 clk/1024 125nsX1024=128us
}

//-----------------------------------------------------------------------------
//  Timer/Counter0 Overflow Handler
//-----------------------------------------------------------------------------
ISR(TIMER0_OVF_vect)
{
    TCNT0 = TCNT0_InitVal;  // Clear Time/Counter0

    PINB |= _BV(PB1);       // Invert PB1

}

//-----------------------------------------------------------------------------
//  Main
//-----------------------------------------------------------------------------
int main()
{
    DDRB  |= _BV(PB1);  // Set PB1 Output
    PORTB |= _BV(PB1);  // Set PB1 High

    initTimer0();   // Initialize Timer/Counter0
    sei();          // Interrupt Enable

    while (1) {
        asm("sleep"::);
    }

    return 0;
}

Wait10usTest †

Timer/Counter0を使って、分解能10usのタイマー関数を実現したサンプルプログラム。

//-----------------------------------------------------------------------------
//  ATmega168
//  Internal 8 MHz Osc.
//  (1/8M = 125 ns)
//-----------------------------------------------------------------------------

#include <avr/io.h>

//-----------------------------------------------------------------------------
//  wait 10 us using Timer/Counter0
//-----------------------------------------------------------------------------
void wait10us(int times)
{
    int count;

    TCCR0B = 0x02;  // Start Timer/Counter0 clk/8 125nsX8 = 1us
    TCNT0  = 0x00;  // Clear Counter

    // wait timesX10us
    for (count = 0; count < times; count++)
    {
        while( TCNT0 < 10 );    // 1usX10 = 10us
        TCNT0 = 0x00;
    }
}

//-----------------------------------------------------------------------------
//  Main
//-----------------------------------------------------------------------------
int main()
{
    DDRB  |= _BV(PB1);  // Set PB1 Output
    PORTB |= _BV(PB1);  // Set PB1 High

    while (1) {
        wait10us(100);      // wait 1ms
        PINB |= _BV(PB1);   // invert PB1
    }
}

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