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//----------------------------------------------------------------------------------
//      Prevodnik RS232 <--> RS485
//      pri startbitu na RS232 zapne okamzite vysilac pokud nejsou detekovana data z RS485.
//----------------------------------------------------------------------------------

#include <avr/io.h>
#include <avr/interrupt.h>
#include <stdlib.h>
#include <ctype.h>
#include <avr/eeprom.h>
#include <avr/pgmspace.h>

#define POVOLOVAK_LOW   PORTB &= ~(1<<PB3)
#define POVOLOVAK_HIGH  PORTB |= (1<<PB3)
#define DATA    (PIND & (1<<PD1))

volatile unsigned int preteceni;
unsigned int bit;
unsigned int bitdelay;
unsigned int last;
unsigned int cas;

ISR(TIMER0_OVF_vect)   // interrupt od preteceni casovace
{
  preteceni++;                  // kdyz pretece, poznamenej to.
}


// ------------------------------------------------------------------
//      Main
// ------------------------------------------------------------------
int main(void)
{

  DDRD |= (1<<DDD5);
  DDRB |= (1<<DDB3);

  TIMSK |= (1 << TOIE0); // Enable timer overflow interrupt 
  TCCR0B |= (1 << CS10);  // Set up timer 
  sei();   // enable interrupts

  while(1)
  {
        if(!DATA)   // kdyz je 0 na datech 
        { 
          POVOLOVAK_HIGH;    // zapni vysilani

          cas = 0xFFFF;
          bitdelay = 0;
                          
          for (bit=0;bit<=7;bit++) // odpocitej dobu 8mi bitu 
          {
                last = DATA;
            TCNT0 = 0;                                  // vynuluj citac pred tim, než smazes preteceni, protoze jinak by se mohlo stat, ze se nastavi preteceni driv, nez ma
            preteceni = 0;

            while ((TCNT0+preteceni*0x0100) <= cas) // bit poznas tak, ze je to nejmensi nalezena delka trvaleho stavu
                {
                  bitdelay=TCNT0+preteceni*0x0100;
                  if(DATA != last)                      // zkontroluj, jestli se nezmenil stav dat.
                  {
                    if (bitdelay < cas) cas = bitdelay; //kdyz se zmenil a trvalo to kratsi dobu nez pred tim poznemenej, jak dlouho to trvalo 
                        break;
                  }
        }
          }
//        while (!DATA);                                // cekani na stop bit

/*        for (bit=2;bit >= 0;bit--)    // odpocitej dva stopbity
          {
            TCNT0 = 0;                                  // zacni znova merit cas zacatku stopbitu
                preteceni=0;

            while ((TCNT0+preteceni*0x0100) <= cas) 
                {
                  if(!DATA) break;
        }
          }*/
    }
    else  POVOLOVAK_LOW;        // kdyz je 1 prepni na prijem 
  }
  return(0);
}