7-segment numeric display

The Study board is equipped with 7-segment LED display and its driver A6275 (datasheet). The driver is connected to controller ports PORTC and PORTG.

the schematics is shown below. The latch is connected to PORTG2, Serial to PORTC6 and clock to PORTC7.

/* 
Basic ver 3 demo program
7-seg function and demo
Raivo Sell/Erki Leitaru
*/
#define F_CPU 14745600UL
 
#include <avr/io.h>
#include <util/delay.h>
 
#define SET(x) |= (1<<x)  //define the high bit in port x
#define CLR(x) &=~(1<<x)  //define the low bit in port x
#define bit_get(p,m) ((p) & (m)) //returns 1 if bit is set, otherwise returns 0
#define BIT(x) (0x01 << (x))
 
void write_display (void);
void nop_delay(int count);
 
int i;//for cycle
int digit;//digit to display on segment
int nr;//segment map representation of the digit
int delta;//to create a counting effect
int num = 0;
char buffer[7];
 
void nop_delay(int count){
	unsigned int j;
	for (j=0; j<count;j++)	{asm volatile ("nop");}
}
 
void write_display (void) {
	 switch (digit) //table read to get segment map representation of the digit
	 {
		 case 0 : nr = 0b00111111;break; //every bit corresponds to one segment
		 case 1 : nr = 0b00000110;break; //"1"
		 case 2 : nr = 0b01011011;break; //"2" and so on
		 case 3 : nr = 0b01001111;break; 
		 case 4 : nr = 0b01100110;break; 
		 case 5 : nr = 0b01101101;break; 
		 case 6 : nr = 0b01111100;break; 
		 case 7 : nr = 0b00000111;break;
		 case 8 : nr = 0b01111111;break; 
		 case 9 : nr = 0b01100111;break;  
		 default: nr = 0b01111001;//E
	 }
 
	 PORTG CLR (2); //latch low
	 for(i=7; i>=0; i--) //for every bit in the byte
	 {
	 	//if bit is set, sets the data out pin
		if (bit_get(nr, BIT(i))) PORTC SET (6); //serial out
		else PORTC CLR (6); //serial out
 
		PORTC SET (7); //clock high
		nop_delay(8);//series of one cycle delays to ensure required timing (according to datasheet)
 
		PORTC CLR (7); //clock low
		nop_delay(8);
	 }
	 PORTG SET (2); //latch high
 
}
 
int main(void){
 
	//7-seg init
    PORTC = 0xFF; // set output high -> turn all LEDs off
    DDRC  = 0xF8; // PC0...PC2 -> input; PC3...PC5 -> output for LED; PC7 & PC6 outputs for clock and data
	DDRG  = 0x04;//PG2 is latch output
 
	digit = 8;
	delta = 1;//increment or decrement
 
	while(1) {
		num++;
		_delay_ms(1000);
		digit=digit+delta;//change digit by delta
		if(digit>8) {delta=-1*delta;};//upper limit
		if(digit<1) {delta=-1*delta;};//lower limit
		write_display();
	}
}

This example uses pin operations file "pin.h"

//
// Simple up/down counting single 7-segment digit example.
//
// Raivo Sell, Erki Leitaru, Mikk Leini
//
// 2009
//
 
// Include avrlibc
#include <avr/io.h>
#include <util/delay.h>
 
// Include common library
#include "pin.h"
 
// Configure pins
#define SEGMENT_DISPLAY_LATCH      PORTPIN(G, 2)
#define SEGMENT_DISPLAY_DATA_OUT   PORTPIN(C, 6)
#define SEGMENT_DISPLAY_CLOCK      PORTPIN(C, 7)
 
//
// 7 segment display initialization
//
void segment_display_init(void)
{
	// Set latch, data out and clock pins as output
	pin_setup_output(SEGMENT_DISPLAY_LATCH);
	pin_setup_output(SEGMENT_DISPLAY_DATA_OUT);
	pin_setup_output(SEGMENT_DISPLAY_CLOCK);	
}
 
//
// Digit writing to 7 segment display
//
void segment_display_write(unsigned char digit)
{
	unsigned char map;
 
	// Decimal to segment map
	switch (digit)
	{
		case 0 : map = 0b00111111; break; // Every bit corresponds to one segment
		case 1 : map = 0b00000110; break; // "1"
		case 2 : map = 0b01011011; break; // "2"
		case 3 : map = 0b01001111; break; // "3" and so on
		case 4 : map = 0b01100110; break; 
		case 5 : map = 0b01101101; break; 
		case 6 : map = 0b01111100; break; 
		case 7 : map = 0b00000111; break;
		case 8 : map = 0b01111111; break; 
		case 9 : map = 0b01100111; break;  
		default: map = 0b01111001;        // E like Error
	}	
 
	// Latch low
	pin_clear(SEGMENT_DISPLAY_LATCH);
 
	// Send every bit in the byte. MSB (most significant bit) first.
	for (signed char i = 7; i >= 0; i--)
	{
		// If bit is set, sets the data out pin, otherwise not		
		pin_set_to(SEGMENT_DISPLAY_DATA_OUT, IS_BIT_SET(map, i));
 
		// Clock high for certain period
		pin_set(SEGMENT_DISPLAY_CLOCK)
		_delay_us(1);
 
		// Clock low for certain period		
		pin_clear(SEGMENT_DISPLAY_CLOCK)
		_delay_us(1);
	}
 
	// Latch high 	
	pin_set(SEGMENT_DISPLAY_LATCH);
}
 
//
// Program entrance function
//
int main(void)
{ 
	unsigned char digit = 0; // Digit to display on segment
	signed char delta = 1;   // Digit modifying value
 
	//digit = int (void) { return 2; }; 
 
	// 7 segment display initialization
	segment_display_init();	 
 
 	// Endless loop
	while (1)
	{
		// Write digit
		segment_display_write(digit);
 
		// Increase digit value by delta (which can be negative also)
		digit += delta;
 
		// Swap counting direction on 0 and 9
		if (digit == 0) delta = +1;
		if (digit == 9) delta = -1;		
 
		// Wait 1000 ms
		_delay_ms(1000);
	}
}

7-segment display in Wikipedia