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Код: Выделить всё

void USI_TWI_Master_Initialise( void )
{
  PORT_USI |= (1<<PIN_USI_SDA);           // Enable pullup on SDA, to set high as released state.
  PORT_USI |= (1<<PIN_USI_SCL);           // Enable pullup on SCL, to set high as released state.
  
  DDR_USI  |= (1<<PIN_USI_SCL);           // Enable SCL as output.
  DDR_USI  |= (1<<PIN_USI_SDA);           // Enable SDA as output.
  
  USIDR    =  0xFF;                       // Preload dataregister with "released level" data.
  USICR    =  (0<<USISIE)|(0<<USIOIE)|                            // Disable Interrupts.
              (1<<USIWM1)|(0<<USIWM0)|                            // Set USI in Two-wire mode.
              (1<<USICS1)|(0<<USICS0)|(1<<USICLK)|                // Software stobe as counter clock source
              (0<<USITC);
  USISR   =   (1<<USISIF)|(1<<USIOIF)|(1<<USIPF)|(1<<USIDC)|      // Clear flags,
              (0x0<<USICNT0);                                     // and reset counter.
}

Код: Выделить всё

  PORT_USI |= (1<<PIN_USI_SCL);                     // Release SCL.
  while( !(PIN_USI & (1<<PIN_USI_SCL)) );          // Verify that SCL becomes high.
#ifdef TWI_FAST_MODE
  _delay_us( T4_TWI/4 );                         // Delay for T4TWI if TWI_FAST_MODE
#else
  _delay_us( T2_TWI/4 );                         // Delay for T2TWI if TWI_STANDARD_MODE
#endif

/* Generate Start Condition */
  PORT_USI &= ~(1<<PIN_USI_SDA);                    // Force SDA LOW.
  _delay_us( T4_TWI/4 );                         
  PORT_USI &= ~(1<<PIN_USI_SCL);                    // Pull SCL LOW.
  PORT_USI |= (1<<PIN_USI_SDA);                     // Release SDA.