Code

// blink.c compiled with codevisionavr 1.0006 // wichit sirichote 26-02-43 #include <90s8535.h> #include <delay.h> #define xtal 8000000 unsigned char counter1,flag1; bit enable_tone,off_hook; void tick_wait(){ while((tifr&0x01) == 0); //cputick <10); tcnt0 = 256-75; //78; // reload timer 0 for 100hz tick generation tifr |= 0x01; // clear timer 0 overflow flag by writing '1' } void task1(){ counter1++; if (counter1 >100) {portc ^= 0x80; counter1 = 0; flag1 ^= 0x01; // toggle flag1.0 enable_tone ^= 1; // toggle enable_tone bit } } void on_tone(){ tccr2 = 0x1e; }

// enable oc2 toggle for tone generation

void off_tone(){ tccr2 = 0x2e; }

// turn oc2 low

void test_tone(){ if (enable_tone == 1) //((flag1&0x01) != 0) on_tone(); else off_tone(); } void main() { // initialize corresponding port ddra=0x00; /* all port a is ddrb=0xff; /* all port b is ddrc=0xff; /* all port c is ddrd=0x80; /* port d is input portb=0x00; portc=0x00;

input output output except

*/ */ */ pd7 for oc2 output

flag1 = 0; // timer0 is used for system 10ms tick timsk = 0x01; tccr0 = 0x05;

// timer 0 overflow enable // start timer0 with clk/1024

*/

// timer2 is used for 550hz tone generation, the real output measured via fluke83 is 558hz ocr2 = 28; // toggle oc2 every 1/1116hz or 558hz output frequency tccr2 = 0x1e; // start timer2 with pclk/256, reset timer2 when matched while (1) { tick_wait(); test_tone(); //on_tone(); task1(); } }

// 10ms tick