// 4 x 7 digit LED display control - no interrupt

const int8_t numbers [10] = {20, 215, 76, 69, 135, 37, 36, 87, 4, 5}; 

volatile uint8_t Digit_X000, Digit_0X00, Digit_00X0, Digit_000X;	// store single digits
volatile uint8_t active_digit = 0;									// active digit

void initialize_LED_display()
{	DDRD = 0b11111111;	
	DDRC = 0b00001111;	
}

// Write number at indicated position to display
void digit (uint8_t value, uint8_t pin)
{	PORTD = numbers[value];			// number output
	PORTC &= ~(1 << pin);			// Low = current digit on
}

// distribute number to digits
void number_output (uint16_t number)       
{	Digit_X000 = number/1000; number %= 1000;
	Digit_0X00 = number/100;  number %= 100;
	Digit_00X0 = number/10;	  number %= 10;
	Digit_000X = number;
}

void refresh() 
{	PORTC = 0b00001111; // Digits off
	if(active_digit == 0) digit (Digit_000X, PC0);
	if(active_digit == 1) digit (Digit_00X0, PC1);
	if(active_digit == 2) digit (Digit_0X00, PC2);
	if(active_digit == 3) digit (Digit_X000, PC3);

	active_digit ++;				
	if (active_digit == 4) active_digit = 0;			
}